WO2002023640A1 - Nitride compound semiconductor light emitting device having a tunnel junction structure and fabrication method thereof - Google Patents

Nitride compound semiconductor light emitting device having a tunnel junction structure and fabrication method thereof Download PDF

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Publication number
WO2002023640A1
WO2002023640A1 PCT/KR2001/001530 KR0101530W WO0223640A1 WO 2002023640 A1 WO2002023640 A1 WO 2002023640A1 KR 0101530 W KR0101530 W KR 0101530W WO 0223640 A1 WO0223640 A1 WO 0223640A1
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WIPO (PCT)
Prior art keywords
layer
ohmic contact
nitride semiconductor
type
light emitting
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PCT/KR2001/001530
Other languages
French (fr)
Inventor
Gye-Mo Yang
Seong-Ran Jeon
Ki-Soo Kim
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Optowell Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from KR20000053982A external-priority patent/KR100380536B1/en
Priority claimed from KR10-2000-0066637A external-priority patent/KR100395660B1/en
Priority claimed from KR10-2000-0068925A external-priority patent/KR100384597B1/en
Application filed by Optowell Co., Ltd. filed Critical Optowell Co., Ltd.
Publication of WO2002023640A1 publication Critical patent/WO2002023640A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/26—Materials of the light emitting region
    • H01L33/30—Materials of the light emitting region containing only elements of group III and group V of the periodic system
    • H01L33/32—Materials of the light emitting region containing only elements of group III and group V of the periodic system containing nitrogen
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
    • H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
    • H01S5/34333—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/04—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a quantum effect structure or superlattice, e.g. tunnel junction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/042—Electrical excitation ; Circuits therefor
    • H01S5/0421—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/305—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure

Definitions

  • the present invention relates to a nitride semiconductor light emitting device having tunnel junction layer and manufacturing method thereof, and more particularly, to a nitride semiconductor light emitting device and manufacturing method thereof in which a tunnel junction layer is introduced to substantially simplify the manufacturing process and enhance the light emission efficiency.
  • GaAs-based light emitting devices generally use the GaAs substrate.
  • the substrate is the same material as a thin film formed on the substrate, an epitaxial growth of the thin film is easy, and a thermal crack due to a difference in the thermal expansion coefficient can be prevented.
  • the substrate itself is semiconductor, it has some conductivity, and accordingly has an advantage in that ohmic contact electrode can be formed on rear surfaces of the epitaxial layer and the substrate.
  • GaN-based nitride semiconductor light emitting device is formed on an insulating substrate such as sapphire (A1 2 0 3 ) .
  • a GaN thin film having a good quality can be obtained only at a high temperature of approximately 1,000 °C or more. Because of the necessity of the high temperature growth, it is difficult to obtain a substrate having a lattice constant matched with that of the GaN thin film and a similar thermal expansion coefficient to that of the GaN thin film.
  • the sapphire substrate has a lattice mismatch of approximately 16% compared with the GaN thin film, and the SiC substrate has a lattice mismatch of approximately 3.5%.
  • the GaN-based nitride semiconductor light emitting device uses insulator as the substrate, it has a drawback in that an ohmic contact metal electrode cannot be formed directly on the substrate. Accordingly, a complicated process is requested to form the ohmic contact metal electrode .
  • Figs, la through lj are sectional views for describing a conventional method of manufacturing a nitride semiconductor light emitting device.
  • Fig. la is a sectional view for describing steps of forming an n type lower ohmic contact layer 30, an active layer 40, and a p type upper ohmic contact layer 80.
  • n type lower ohmic contact layer 30 made of n type GaN.
  • active layer 40 on the n type lower ohmic contact layer 30 is formed the active layer 40.
  • the active layer 40 has a double heterostructure, a single quantum well structure, or a multiple quantum wells structure.
  • the p type upper ohmic contact layer 80 which is made of p type GaN.
  • an etch stopper film 110 is formed on a selected region of the p type upper ohmic contact layer 80.
  • Fig. lb is a sectional view for describing a mesa etch step. Specifically, by using the etch stopper film 110 as an etch mask, a dry etch is carried out until the n type lower ohmic contact layer 30 is exposed, and then the etch stopper film 110 is removed.
  • Figs, lc through le are sectional views for describing steps of forming a p type semitransparent upper ohmic contact layer 130.
  • a photosensitive film is formed, and is then patterned to form a first photosensitive film pattern 120a exposing the p type upper ohmic contact layer 80.
  • the p type semitransparent ohmic contact electrode layer 130 made by a combination selected from a metal group consisting of Ni, Pt, Pd, Au, and the like to a thickness ranged from 50 A to 200 A.
  • the first photosensitive film pattern 120a is removed such that the p type semitransparent ohmic contact electrode layer 130 remains only on the p type upper ohmic contact layer 80.
  • the resultant substrate is thermally annealed such that the p type semitransparent ohmic contact electrode layer 130 is ohmic-contacted with the p type upper ohmic contact layer 80.
  • Figs. If through lh are sectional views for describing steps of forming an n type ohmic contact electrode 140.
  • a photosensitive film is formed on the resultant structure of Fig. le, and is patterned to form a second photosensitive film pattern 120b exposing the n type lower ohmic contact layer 30.
  • the n type ohmic contact electrode layer 140 of metal.
  • the n type ohmic contact electrode layer 140 has a stack structure in which Ti film of approximately 500 A and Al film of approximately 2,000 A are stacked in the order named.
  • the second photosensitive film pattern 120b is removed such that the n type ohmic contact electrode layer 140 remains only on the n type lower ohmic contact layer 30.
  • the resultant substrate is thermally annealed such that the n type ohmic contact electrode layer 140 is ohmic-contacted with the n type lower ohmic contact layer 30.
  • Figs, li and lj are sectional views for describing steps of forming a p type bonding electrode layer 150a.
  • a third photosensitive film pattern 120c of exposing the p type semitransparent ohmic contact electrode layer 130 is formed.
  • the p type bonding electrode layer 150 is formed on the entire surface of the resultant structure in which the third photosensitive film pattern 120c is formed.
  • the third photosensitive film pattern 120c is removed such that the p type bonding electrode layer 150 remains only on the p type semitransparent ohmic contact electrode layer 130.
  • the electrode cannot be formed on the substrate directly. So, the n type lower ohmic contact layer 30 is first formed, and then the n type ohmic contact electrode layer 140 electrically connected thereto is formed.
  • twice lift-off processes and twice thermal annealing processes for ohmic contact should be carried out.
  • both of the p type semitransparent ohmic contact electrode layer 130 and the p type bonding electrode layer 150 should be formed.
  • the conventional method for forming the nitride semiconductor light emitting device has drawbacks in that its manufacturing process is complicated and it taken a very long time. Further, the p type GaN has a high resistance. Therefore, in order for current to flow through the entire surface of the p type upper ohmic contact layer, the p type semitransparent ohmic contact electrode layer 130 should be formed to cover the entire surface of the p type upper ohmic contact layer 80.
  • the current flowing through the p type bonding electrode layer 150 continues to flow through the entire surface of the p type upper ohmic contact layer 80 via the p type semitransparent ohmic contact layer 130, and accordingly light is emitted upwardly from not a portion beneath the p type bonding electrode layer 80 but a side portion thereof.
  • the p type semitransparent ohmic contact electrode layer 130 is formed in a thickness of 200 A or less to have transparency as aforementioned. Since there are few materials having both of the transparency and the conductivity, and it is not easy to introduce such the material into the process, metal materials are very thinly formed to obtain the transparency and the conductivity.
  • the thickness of the p type semitransparent ohmic contact electrode layer 130 should be sensitively controlled, so that a process margin becomes very small. Also, since the p type semitransparent ohmic contact electrode layer 130 is not completely transparent but is semitransparent, light is absorbed therein to some degree and thereby light emission efficiency is lowered.
  • a contact resistance between the p type upper ohmic contact layer 80 and the p type semitransparent ohmic contact electrode layer 130 is very large. It was reported that in case of the n type ohmic contact electrode layer 140, a low contact resistance of 10 ⁇ 6 ⁇ or less can be obtained by thermally annealing Ti/Al layer at a temperature of 900 °C for 30 seconds, but it has been reported that the p type ohmic contact electrode layer 130 still has a contact resistance higher than the n type ohmic contact electrode layer 140.
  • a technical object of the invention to newly introduce a thin pn tunnel junction layer doped to a high concentration and thereby provide a nitride semiconductor light emitting device having a low driving voltage and a high light emission efficiency. It is another object of the invention to provide a method for manufacturing a nitride semiconductor light emitting device which is adapted to accomplish the above technical object . To accomplish the technical object and other advantages, there is a nitride semiconductor light emitting device according to a first embodiment of the present invention.
  • the light emitting device comprises: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; an active layer formed on the lower ohmic contact layer and made of a nitride semiconductor;- a tunnel junction layer formed on the active layer and having a structure in which a p type nitride semiconductor layer and an n type nitride semiconductor layer each of which is doped with dopants having a concentration of 1 x 10 18 - 1 x 10 21 cm -3 are sequentially stacked; an upper ohmic contact layer formed on the tunnel junction layer and made of the n type nitride semiconductor layer; and an n type ohmic contact metal electrode layer which is ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layers being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer.
  • the light emitting device comprises: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; a light emitting part formed on the lower ohmic contact layer and having a structure in which an active layer and a tunnel junction layer are sequentially and repeatedly stacked, the active layer being made of a nitride semiconductor, the tunnel junction layer having a structure in which an n-type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 10 18 - 1 x 10 21 cm -3 is stacked on a p-type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 10 18 - 1 x 10 21 cm -3 ; an upper ohmic contact layer formed on the light emitting part and made of n type nitride semiconductor; and an n type o
  • the light emitting device comprises: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; multiple active layers formed on the lower ohmic contact layer and made of a nitride semiconductor; a tunnel junction layer interposed between the multiple active layers and having a structure in which a p type nitride semiconductor layer and an n type nitride semiconductor layer each of which is doped with dopants having a concentration of 1 x 10 18 - 1 x 10 21 cm -3 are sequentially stacked; an upper ohmic contact layer formed on an uppermost active layer out of the multiple active layers and made of a p type nitride semiconductor; and an n type ohmic contact metal electrode layer and a p type ohmic contact metal electrode which are respectively ohmic-contacted with the lower ohmic contact layer and the upper
  • the light emitting device comprises: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; a tunnel junction layer formed on the lower ohmic contact layer and having a structure in which an n type nitride semiconductor layer and a p type nitride semiconductor layer each of which is doped with dopants having a concentration of 1 x 10 18 - 1 x 10 21 cm "3 are sequentially stacked; an active layer formed on the tunnel junction layer and made of a nitride semiconductor; an upper ohmic contact layer formed on the active layer and made of n type nitride semiconductor; and an n type ohmic contact metal electrode layer which is ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layers being respectively provided on the lower
  • the light emitting device comprises: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; a light emitting part formed on the lower ohmic contact layer and having a structure in which a tunnel junction layer and an active layer are sequentially and repeatedly stacked, the tunnel junction layer having a structure in which a p type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 10 18 - 1 x 10 21 cm -3 is stacked on an n type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 10 18 - 1 x 10 21 cm -3 , and the active layer being made of a nitride semiconductor; an upper ohmic contact layer formed on the light emitting part and made of n-type nitride semiconductor; and an n type ohmic contact
  • a delta doping layer may be interposed between the p type nitride semiconductor layer of the tunnel layer and the n type nitride semiconductor layer of the tunnel layer.
  • the delta doping layer is formed by delta-doping Si in a planar concentration of 1 x 10 11 - 1 x 10 14 cm -2 .
  • the method comprises: a first step of forming an n type lower ohmic contact layer made of n type nitride semiconductor on a substrate; a second step of forming an active layer made of nitride semiconductor on the n type lower ohmic contact layer; a third step of forming a tunnel junction layer on the active layer, the tunnel junction layer having a structure in which a p type nitride semiconductor layer and an n type nitride semiconductor layer are sequentially stacked; a fourth step of forming an n type upper ohmic contact layer made of n type nitride semiconductor on the tunnel junction layer; a fifth step of sequentially mesa-etching the n type upper ohmic contact layer, the tunnel junction layer, and the active layer such that the lower ohmic contact layer is exposed; and a sixth step of simultaneously forming an n type ohmic contact metal electrode layer which is ohmic-contacted with the n type upper ohmic contact layer and the n type
  • Figs, la through lj are sectional views for describing a conventional method of manufacturing a nitride semiconductor light emitting device
  • Fig. 2 is a sectional view for describing a nitride semiconductor light emitting device in accordance with a first embodiment of the present invention
  • Figs. 3a through 3e are sectional views for describing a manufacturing method of the nitride semiconductor light emitting device of Fig. 2;
  • Figs .4 and 5 are sectional views for describing a nitride semiconductor light emitting device in accordance with a second embodiment of the invention.
  • Fig. 6 is a sectional view for describing a nitride semiconductor light emitting device in accordance with a third embodiment of the invention.
  • Fig. 7 is a sectional view for describing a nitride semiconductor light emitting device in accordance with a fourth embodiment of the invention.
  • Fig. 2 is a sectional view for illustrating a nitride semiconductor light emitting device grown by a MOCVD (Metalorganic Chemical Vapor Deposition) in accordance with a first embodiment of the invention.
  • MOCVD Metalorganic Chemical Vapor Deposition
  • superscript symbols "++", “+”, “- attached adjacent to the conductivity type letters p" or "n”, represent relative doping concentrations. As it travels in the order of "++", “+”, “-”, doping concentration becomes low.
  • a buffer layer 21 made of GaN.
  • the substrate 11 there may be used a sapphire substrate (A1 2 0 3 ) has a crystallographic orientation of (0001) c.
  • a substrate made of SiC, GaAs, ZnO, or MgO can be used.
  • the buffer layer 21 is formed to a thickness of 250 A to 300 A at a temperature of 560 °C and a pressure of 300 torr.
  • the buffer layer 21 may be made of A1N, AlGaN, or InGaN .
  • n + type lower ohmic contact layer 31 made of Si-doped GaN.
  • n + type lower ohmic contact layer 31 serves to make a role in buffering occurrence of microcracks in the n + type lower ohmic contact layer 31 and layers formed thereon due to the differences of lattice constants and thermal expansion coefficients.
  • an active layer 41 capable of radiating light having a wavelength of 370 nm to 600 nm.
  • the active layer 41 is formed at a temperature of 750 °C, and at this time, a supply flow of used TMGa is 3.74 ⁇ mol/min.
  • the active layer 41 has a double heterostructure of
  • InGaN ⁇ GaN may have a single quantum well structure of GaN ⁇ InGaN ⁇ GaN, or a multiple quantum well structure of
  • the p " type clad layer 53 is formed at an approximately 1,130 °C, and at this time, the supply flows of TMGa, ammonia, and Cp 2 Mg as used, are respectively 112 ⁇ mol/min, 41/min, and 1.07 ⁇ mol/min.
  • the p-type clad layer 53 may be made of Al x Ga ⁇ - x N, wherein x is O ⁇ x ⁇ 0.5.
  • the tunnel junction layer 55 has a structure in which a p ++ type GaN layer 51 and an n ++ type GaN layer 61 are sequentially stacked and a delta doping layer 57 is sandwiched therebetween.
  • the delta doping layer 57 is indicative of a layer in which Si is very thinly doped into a surface of the GaN layer.
  • n type dopants such as 0, Ge, or Sn may be delta-doped.
  • p type dopants such as Zn, Cd, Mg, or Be may be delta-doped.
  • the delta doping layer 57 may have a stack structure in which an Mg-doped delta doping layer and a Si-doped delta doping layer are sequentially stacked.
  • the tunnel junction layer 55 has the stack structure in which the p ++ type GaN layer 51 and the n ++ type GaN layer 61 are sequentially stacked and the delta doping layer 57 is sandwiched therebetween, it can be modified by another example in which only the n ++ type delta doping layer is formed on the p ++ type GaN layer 51 without the n ++ type GaN layer 61.
  • On the tunnel junction layer 55 there is formed an n ⁇ type clad layer 63 to a thickness of 10 A to 10,000 A.
  • the n ' type clad layer 63 is comprised of Si-doped GaN, and is formed by respectively supplying TMGa, ammonia, and SiH 4 at flow rates of 112 ⁇ mol/min, 4 1/min, and 1.72 nmol/min.
  • On the n ⁇ type clad layer 63 there is formed an n + type upper ohmic contact layer 71 made of Si-doped GaN.
  • the n + type upper ohmic contact layer 71 and the n + type lower ohmic contact layer 31 are respectively ohmic-contacted with an n type ohmic contact metal electrode.
  • the structure of Fig. 2 is further provided with the tunnel junction layer 55.
  • the light emission principle in the nitride semiconductor light emitting device of Fig. 2 can be briefly described as follows. If a reverse bias is applied through the n type ohmic contact metal electrode layer 141 to the tunnel junction layer 55, electrons in the valence band of the p ++ type GaN layer 51 makes a tunneling into the n ++ type GaN layer 61. Accordingly, holes are created at vacant sites where the electrons were transferred in the p ++ GaN layer 51. These holes are injected into the active layer 41 via the p ⁇ type clad layer 53. These holes injected into the active layer 41 are recombined with the electrons supplied into the active layer
  • an n ⁇ type clad layer may be further formed between the n + type lower ohmic contact layer 31 and the active layer 41.
  • Figs. 3a through 3e are sectional views for illustrating a method for manufacturing the nitride semiconductor light emitting device of Fig. 2.
  • Fig. 2 since the buffer layer
  • the p ⁇ type clad layer 53, and the n ⁇ type clad layer 63 are not essential elements, descriptions on methods for manufacturing these layers are intentionally omitted.
  • Fig. 3a is a sectional view for illustrating steps of forming the n + type lower ohmic contact layer 31, the active layer 41, the tunnel layer 55, and the n + type upper ohmic contact layer 71.
  • the sapphire substrate (A1 2 0 3 ) having the crystallographic orientation of (0001) c face is heated to a temperature of 1,130 °C, and at the same time TMGa, ammonia, and SiH 4 are respectively introduced at flow rates of 150
  • n type lower ohmic contact layer 31 to a thickness of 3 ⁇ m of Si-doped n type GaN on the substrate 11.
  • active layer 41 having a multiple quantum well structure in which GaN layer having a thickness ranged from 80 A to 85 A, and InGaN layer having a thickness ranged from 15 A to 20 A are alternatively stacked by six periods .
  • the GaN layer serves as a barrier layer
  • the InGaN layer serves as a well layer.
  • the tunnel junction layer 55 has a stack structure in which a p ++ type GaN layer 51 and an n ++ type GaN layer 61 are sequentially stacked. At this time, it is desirous that a delta doping layer 57 is further formed between the p ++ type GaN layer 51 and the n ++ type GaN layer 61.
  • the p ++ type GaN layer 51 has a thickness ranged from 10 A to 1 , 000 A, and is formed to have an Mg-doped concentration of 1 x 10 18 - 1 x 10 21 crrf 3 by introducing TMGa, ammonia, and Cp 2 Mg at flow rates of 112 ⁇ mol/min, 4 1/min, and 2.14 nmol/ in, respectively.
  • the delta doping layer 57 is formed by growing the p type GaN layer 51, after an elapse of a growth stop time of 1 - 300 seconds, and introducing ammonia at a flow rate of 10 seconds to 30 seconds, and SiH4 at a flow rate of 50.22 nmol/min such that Si is delta-doped into the GaN layer at a planar doping concentration of 1 x 10 11 - 1 x 10 14 cm -2 .
  • the n ++ type GaN layer 61 is formed to a thickness ranged from 10 A to 1,000 A by introducing TMGa, ammonia, and SiH 4 at flow rates of 112 ⁇ mol/min, 4 1/min, and 50.22 nmol/min, respectively such that it has a doping concentration of 1 x 10 18 - 1 x 10 21 cm "3 .
  • the n + type upper ohmic contact layer 71 having a thickness ranged from 100 A to 5,000 A and made of Si-doped n type GaN is formed by introducing TMGa, ammonia, and SiH 4 at flow rates of 112 ⁇ mol/min, 4 1/min, and 3.74 nmol/min, respectively. Afterwards, an etch stopper film 111 of Si0 2 is formed on a selected region of the n + type upper ohmic contact layer 71.
  • Fig. 3b is a sectional view for illustrating a mesa etch step. Specifically, a dry etch is carried out by using the etch stopper film as an etch mask using an ICP (Inductively coupled plasma) , to thereby remove the etch stopper film 111.
  • ICP Inductively coupled plasma
  • Figs. 3c through 3e are sectional views for illustrating steps of forming the n type ohmic contact metal electrode layer
  • n type ohmic contact electrode layer 141 made of a metal selected from a group consisting of Ti, Al, andAu. Afterwards, the photosensitive film pattern 121a is removed to form the n type ohmic contact metal electrode layer 141 only on the n type upper ohmic contact layer 71 and the n type lower ohmic contact layer 31.
  • the resultant substrate is thermally annealed at a temperature range of 350 - 1, 000 °C such that the n type ohmic contact metal electrode layer 141 is ohmic-contacted with the n type upper ohmic contact layer 71 and the n type lower ohmic contact layer 31, so that the nitride semiconductor light emitting device is completed.
  • Fig. 4 is a sectional view for illustrating a nitride semiconductor light emitting device in accordance with a second embodiment of the present invention.
  • the structure shown in Fig. 4 has a difference from the structure shown in Fig. 2 in that the light emitting part in the structure shown in Fig. 2 is comprised of the active layer 41, the p " type clad layer 53, the tunnel junction layer 55, and the n " type clad layer 63 while a light emitting part in the structure shown in Fig. 4 has a stack structure in which they are alternatively and repeatedly stacked.
  • Fig. 4 there is shown a stack structure in which they are repeatedly by twice times and stacked.
  • the light emitting part has a stack structure in which a first active layer 41' , a first p " type clad layer 53' , a first tunnel junction layer 55' , a first n ⁇ type clad layer 63' , a second active layer 41", a second p “ type clad layer 53", a second tunnel junction layer 55", and a second n " type clad layer 63" are sequentially stacked.
  • the first active layer 41' and the second active layer 41" may emit lights having different wavelengths or light having an identical wavelength.
  • the first active layer 41' and the second active layer 41" emit lights having different wavelengths
  • yellow light is emitted from the first active layer 41' and blue light is emitted from the second active layer 41"
  • white light is output on the whole.
  • the first active layer 41' and the second active layer 41" both emit a light having the same wavelength
  • the light is dually output and thereby light emission efficiency is increased.
  • This increase in the light emission efficiency becomes larger as the region of a depletion layer is smaller, the barrier height is lower, and the interface of tunnel junction is more abruptly formed in the first tunnel junction layer 55' and the second tunnel junction layer 55" respectively such that a tunneling occurs with ease. This is because as the interface of tunnel junction is formed more abruptly, less the lights generated from the first and second active layers 41' and 41" are lost.
  • An increase in such the light emission efficiency occurs more largely due to the existence of the delta doping layers 57' and 57".
  • the multiple active layers 41' and 41" are formed, there are advantages in that an input of a single electric power allows a combination of two colors or more, and an acquisition of a high luminance irradiation having a single wavelength. According to the conventional structure, it is impossible to realize the light emitting device having the multiple active layers.
  • the clad layer is not the essential element.
  • Fig. 5 there is shown a structure in which active layer and tunnel junction layer is three times repeatedly stacked.
  • Fig. 6 is a sectional view for illustrating a nitride semiconductor light emitting device in accordance with a third embodiment of the present invention.
  • the device is characterized in that a tunnel junction layer 55 has a stack structure in which a p type GaN layer 51 and an n type GaN layer 61 are sequentially stacked, and is interposed between two active layers 41' and 41".
  • the device of the present embodiment is characterized in that a p type ohmic contact metal electrode layer 142 is used instead of the n type ohmic contact metal electrode layer 141.
  • a light emitting part has a stack structure in which the first active layer 41', a p ⁇ type clad layer 53, the tunnel junction layer, and the second active layer 41" are sequentially stacked.
  • the p " type clad layer 53 may be omitted.
  • the tunnel junction layer 55 is introduced and thereby the multiple active layers are formed, there are advantages in that an input of a single electric power allows a combination of two colors or more, and an acquisition of a high luminance irradiation having a single wavelength like the second embodiment .
  • Fig. 7 is a sectional view for illustrating a nitride semiconductor light emitting device in accordance with a fourth embodiment of the present invention.
  • the device of Fig. 7 is basically the same as that of Fig. 2, but there is a difference in that an active layer 41 is placed on a tunnel junction layer 55' .
  • the tunnel junction layer 55' has a stack structure in which an n ++ type GaN layer 61 and a p ++ type GaN layer 51 are sequentially stacked, and a delta doping layer 57 is interposed therebetween.
  • the nitride semiconductor light emitting device realized by the single active layer 41 is shown in Fig. 7, it is apparent that a light emitting device realized by multiple active layers can be manufactured as mentioned in the second and third embodiments.
  • the nitride semiconductor light emitting devices according to the present invention introduces tunnel junction layers 55, 55',... so that it becomes possible to form the upper ohmic contact layer 71 using the n + type GaN layer.
  • the present invention uses the n type ohmic contact metal electrode layer 141 for the ohmic contact with the n type upper ohmic contact layer 71. Accordingly, the ohmic contact characteristic with metal is enhanced in comparison with the conventional case, thus the conductivity and the current spreading is increased, and thereby the light emission efficiency of the device is enhanced and the driving voltage is lowered.
  • the n type ohmic contact metal layer 141 which is ohmic-contacted with the n type upper ohmic contact layer 71 and the n type lower ohmic contact layer 31 respectively can be formed by once lift-off process and once thermal annealing process for ohmic contact. To this end, its manufacturing process is very simple and rapid.
  • the n type upper ohmic contact layer 71 is made of n type nitride semiconductor, it has a very good conductivity compared with the conventional case. Accordingly, there is no need to form the p type ohmic contact electrode layer 130 on the entire surface of the p type upper ohmic contact layer 80 and form the p type bonding electrode layer 150 on the p type semitransparent ohmic contact electrode layer 130 like the conventional case, but there is a need to form only the n type ohmic contact metal electrode layer 141 on a selected region of the n type upper ohmic contact layer 71, so that current uniformly flows through the entire surface of the n type upper ohmic contact layer 71.
  • the introduction of the tunnel junction layers 55, 55', ... allows to formmultiple active layers 41, 41' , .... Accordingly, when it is necessary that the active layers 41, 41' , ... emit lights having different wavelengths, lights having different wavelengths can be simultaneously emitted using a single driving voltage, and thereby it becomes possible to emit white light .

Abstract

The nitride compound semiconductor light emitting device of the present invention comprises: a lower ohmic contact layer that is made of n-type nitride compound semiconductor and formed on a substrate; an acitve layer that is made of nitride compound semiconductor and formed on the lower ohmic contact layer; a tunnel junction layer having a stacked structure of a p-type and a n-type nitride compound semiconductor layers successively formed on the active layer, the nitride compound semiconductor lyers being doped with a dopant concentration of 1 X 1018 ~ 1 X 1021 cm-3, respectively; an upper ohmic contact layer that is made of a n-type nitride compound semiconductor and formed on the tunnel junction layer; and n-type ohmic contact metal electrode layers that are located on the lower and upper ohmic contact layers and form ohmic contacts thereto, respectively. According to the present invention, a nitride compound semiconductor light emitting device with low operating voltage and high light emitting efficiency can be obtained with a simple fabrication process by introducing a highly doped thin p-n tunnel junction layer.

Description

NITRIDE COMPOUND SEMICONDUCTOR LIGHT EMITTING DEVICE HAVING A TUNNEL JUNCTION STRUCTURE AND FABRICATION METHOD THEREOF
Technical Field The present invention relates to a nitride semiconductor light emitting device having tunnel junction layer and manufacturing method thereof, and more particularly, to a nitride semiconductor light emitting device and manufacturing method thereof in which a tunnel junction layer is introduced to substantially simplify the manufacturing process and enhance the light emission efficiency.
Background Art
GaAs-based light emitting devices generally use the GaAs substrate. At this time, since the substrate is the same material as a thin film formed on the substrate, an epitaxial growth of the thin film is easy, and a thermal crack due to a difference in the thermal expansion coefficient can be prevented. Further, because the substrate itself is semiconductor, it has some conductivity, and accordingly has an advantage in that ohmic contact electrode can be formed on rear surfaces of the epitaxial layer and the substrate.
However, GaN-based nitride semiconductor light emitting device is formed on an insulating substrate such as sapphire (A1203) . A GaN thin film having a good quality can be obtained only at a high temperature of approximately 1,000 °C or more. Because of the necessity of the high temperature growth, it is difficult to obtain a substrate having a lattice constant matched with that of the GaN thin film and a similar thermal expansion coefficient to that of the GaN thin film. The sapphire substrate has a lattice mismatch of approximately 16% compared with the GaN thin film, and the SiC substrate has a lattice mismatch of approximately 3.5%.
Since the GaN-based nitride semiconductor light emitting device uses insulator as the substrate, it has a drawback in that an ohmic contact metal electrode cannot be formed directly on the substrate. Accordingly, a complicated process is requested to form the ohmic contact metal electrode .
Figs, la through lj are sectional views for describing a conventional method of manufacturing a nitride semiconductor light emitting device.
Fig. la is a sectional view for describing steps of forming an n type lower ohmic contact layer 30, an active layer 40, and a p type upper ohmic contact layer 80. First, on a sapphire substrate 10 is formed the n type lower ohmic contact layer 30 made of n type GaN. Subsequently, on the n type lower ohmic contact layer 30 is formed the active layer 40. The active layer 40 has a double heterostructure, a single quantum well structure, or a multiple quantum wells structure. Thereafter, on the active layer 40 is formed the p type upper ohmic contact layer 80 which is made of p type GaN. Next, on a selected region of the p type upper ohmic contact layer 80 is formed an etch stopper film 110.
Fig. lb is a sectional view for describing a mesa etch step. Specifically, by using the etch stopper film 110 as an etch mask, a dry etch is carried out until the n type lower ohmic contact layer 30 is exposed, and then the etch stopper film 110 is removed.
Figs, lc through le are sectional views for describing steps of forming a p type semitransparent upper ohmic contact layer 130. First, on the entire surface of the resultant structure in which the etch stopper film 110 is removed, a photosensitive film is formed, and is then patterned to form a first photosensitive film pattern 120a exposing the p type upper ohmic contact layer 80.
Afterwards, on the entire surface of the resultant structure in which the first photosensitive film pattern 120a is formed, there is formed the p type semitransparent ohmic contact electrode layer 130 made by a combination selected from a metal group consisting of Ni, Pt, Pd, Au, and the like to a thickness ranged from 50 A to 200 A.
After that, the first photosensitive film pattern 120a is removed such that the p type semitransparent ohmic contact electrode layer 130 remains only on the p type upper ohmic contact layer 80. The resultant substrate is thermally annealed such that the p type semitransparent ohmic contact electrode layer 130 is ohmic-contacted with the p type upper ohmic contact layer 80.
Figs. If through lh are sectional views for describing steps of forming an n type ohmic contact electrode 140. First, a photosensitive film is formed on the resultant structure of Fig. le, and is patterned to form a second photosensitive film pattern 120b exposing the n type lower ohmic contact layer 30. Afterwards, on the entire surface of the resultant structure in which the second photosensitive film pattern 120b is formed, there is formed the n type ohmic contact electrode layer 140 of metal. The n type ohmic contact electrode layer 140 has a stack structure in which Ti film of approximately 500 A and Al film of approximately 2,000 A are stacked in the order named.
Next, the second photosensitive film pattern 120b is removed such that the n type ohmic contact electrode layer 140 remains only on the n type lower ohmic contact layer 30. The resultant substrate is thermally annealed such that the n type ohmic contact electrode layer 140 is ohmic-contacted with the n type lower ohmic contact layer 30.
Figs, li and lj are sectional views for describing steps of forming a p type bonding electrode layer 150a. First, a third photosensitive film pattern 120c of exposing the p type semitransparent ohmic contact electrode layer 130 is formed. Afterwards, on the entire surface of the resultant structure in which the third photosensitive film pattern 120c is formed, there is formed the p type bonding electrode layer 150. Thereafter, the third photosensitive film pattern 120c is removed such that the p type bonding electrode layer 150 remains only on the p type semitransparent ohmic contact electrode layer 130.
In the aforementioned conventional art, since the sapphire substrate 10 is insulator, the electrode cannot be formed on the substrate directly. So, the n type lower ohmic contact layer 30 is first formed, and then the n type ohmic contact electrode layer 140 electrically connected thereto is formed. Thus, in order to form the p type semitransparent ohmic contact electrode layer 130 and the n type ohmic contact electrode layer 140, twice lift-off processes and twice thermal annealing processes for ohmic contact should be carried out. Also, both of the p type semitransparent ohmic contact electrode layer 130 and the p type bonding electrode layer 150 should be formed. Accordingly, the conventional method for forming the nitride semiconductor light emitting device has drawbacks in that its manufacturing process is complicated and it taken a very long time. Further, the p type GaN has a high resistance. Therefore, in order for current to flow through the entire surface of the p type upper ohmic contact layer, the p type semitransparent ohmic contact electrode layer 130 should be formed to cover the entire surface of the p type upper ohmic contact layer 80.
The current flowing through the p type bonding electrode layer 150 continues to flow through the entire surface of the p type upper ohmic contact layer 80 via the p type semitransparent ohmic contact layer 130, and accordingly light is emitted upwardly from not a portion beneath the p type bonding electrode layer 80 but a side portion thereof. Accordingly, the p type semitransparent ohmic contact electrode layer 130 is formed in a thickness of 200 A or less to have transparency as aforementioned. Since there are few materials having both of the transparency and the conductivity, and it is not easy to introduce such the material into the process, metal materials are very thinly formed to obtain the transparency and the conductivity.
However, in order for the p type semitransparent ohmic contact electrode layer 130 to have the transparency, the thickness of the p type semitransparent ohmic contact electrode layer 130 should be sensitively controlled, so that a process margin becomes very small. Also, since the p type semitransparent ohmic contact electrode layer 130 is not completely transparent but is semitransparent, light is absorbed therein to some degree and thereby light emission efficiency is lowered.
Meanwhile, since the p-type GaN has a high resistance, there occurs a drawback in that a contact resistance between the p type upper ohmic contact layer 80 and the p type semitransparent ohmic contact electrode layer 130 is very large. It was reported that in case of the n type ohmic contact electrode layer 140, a low contact resistance of 10~6 Ω or less can be obtained by thermally annealing Ti/Al layer at a temperature of 900 °C for 30 seconds, but it has been reported that the p type ohmic contact electrode layer 130 still has a contact resistance higher than the n type ohmic contact electrode layer 140.
Since it is very difficult to form the p type GaN as the p type upper ohmic contact layer 80 at a high quality, a high driving voltage and low light emission efficiency due to the high contact resistance is raised.
In order to lower the driving voltage for devices, there have been carried out many researches such as decrease in the contact resistance by increase of doping concentration in the p type GaN thin film. Also, in order to enhance the light emission efficiency, there have been actively carried out many structural researches about uses of active layer of InGaN quantum well, and AlGaN clad layer. However, in case of the former, if a supply flow of source raw material containing Mg used as dopants is increased in order to increase the doping concentration, quality of the GaN thin film goes bad considerably, and thereby surface recombination problem is raised. Accordingly, there are technical limits in increasing the doping concentration within the p type GaN thin film.
In case of the latter, if Al composition ratio is increased in order to enhance the carrier confinement efficiency with respect to the AlGaN layer used as the clad layer, crack occurs in the formed thin film. In order to prevent occurrence of this crack, although the Al composition ratio is lowered and thickness of the thin film is increased, the crack occurs likewise. Thereby, device performance such as the light emission efficiency and reproducibility, etc. , goes badly.
In order to improve these problems, there have been many researches but there are technical limits in forming an AlGaN thin film with a high quality.
Detailed description of the invention
Accordingly, it is a technical object of the invention to newly introduce a thin pn tunnel junction layer doped to a high concentration and thereby provide a nitride semiconductor light emitting device having a low driving voltage and a high light emission efficiency. It is another object of the invention to provide a method for manufacturing a nitride semiconductor light emitting device which is adapted to accomplish the above technical object . To accomplish the technical object and other advantages, there is a nitride semiconductor light emitting device according to a first embodiment of the present invention. The light emitting device comprises: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; an active layer formed on the lower ohmic contact layer and made of a nitride semiconductor;- a tunnel junction layer formed on the active layer and having a structure in which a p type nitride semiconductor layer and an n type nitride semiconductor layer each of which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm-3 are sequentially stacked; an upper ohmic contact layer formed on the tunnel junction layer and made of the n type nitride semiconductor layer; and an n type ohmic contact metal electrode layer which is ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layers being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer.
To accomplish the technical object and other advantages, there is a nitride semiconductor light emitting device according to a second embodiment of the present invention. The light emitting device comprises: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; a light emitting part formed on the lower ohmic contact layer and having a structure in which an active layer and a tunnel junction layer are sequentially and repeatedly stacked, the active layer being made of a nitride semiconductor, the tunnel junction layer having a structure in which an n-type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm-3 is stacked on a p-type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm-3; an upper ohmic contact layer formed on the light emitting part and made of n type nitride semiconductor; and an n type ohmic contact metal electrode layer which is ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layers being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer.
To accomplish the technical object and other advantages, there is a nitride semiconductor light emitting device according to a third embodiment of the present invention. The light emitting device comprises: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; multiple active layers formed on the lower ohmic contact layer and made of a nitride semiconductor; a tunnel junction layer interposed between the multiple active layers and having a structure in which a p type nitride semiconductor layer and an n type nitride semiconductor layer each of which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm-3 are sequentially stacked; an upper ohmic contact layer formed on an uppermost active layer out of the multiple active layers and made of a p type nitride semiconductor; and an n type ohmic contact metal electrode layer and a p type ohmic contact metal electrode which are respectively ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layer and the p type ohmic contact metal electrode layer being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer. To accomplish the technical object and other advantages, there is a nitride semiconductor light emitting device according to a fourth embodiment of the present invention. The light emitting device comprises: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; a tunnel junction layer formed on the lower ohmic contact layer and having a structure in which an n type nitride semiconductor layer and a p type nitride semiconductor layer each of which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm"3 are sequentially stacked; an active layer formed on the tunnel junction layer and made of a nitride semiconductor; an upper ohmic contact layer formed on the active layer and made of n type nitride semiconductor; and an n type ohmic contact metal electrode layer which is ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layers being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer.
To accomplish the technical object, there is a nitride semiconductor light emitting device according to a fifth embodiment of the present invention. The light emitting device comprises: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; a light emitting part formed on the lower ohmic contact layer and having a structure in which a tunnel junction layer and an active layer are sequentially and repeatedly stacked, the tunnel junction layer having a structure in which a p type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm-3 is stacked on an n type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm-3, and the active layer being made of a nitride semiconductor; an upper ohmic contact layer formed on the light emitting part and made of n-type nitride semiconductor; and an n type ohmic contact metal electrode layer which is ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layers being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer.
In the above respective embodiments, a delta doping layer may be interposed between the p type nitride semiconductor layer of the tunnel layer and the n type nitride semiconductor layer of the tunnel layer. At this time, the delta doping layer is formed by delta-doping Si in a planar concentration of 1 x 1011 - 1 x 1014 cm-2. To accomplish the another object, there is provided a method for manufacturing a nitride semiconductor light emitting device according to another embodiment of the present invention. The method comprises: a first step of forming an n type lower ohmic contact layer made of n type nitride semiconductor on a substrate; a second step of forming an active layer made of nitride semiconductor on the n type lower ohmic contact layer; a third step of forming a tunnel junction layer on the active layer, the tunnel junction layer having a structure in which a p type nitride semiconductor layer and an n type nitride semiconductor layer are sequentially stacked; a fourth step of forming an n type upper ohmic contact layer made of n type nitride semiconductor on the tunnel junction layer; a fifth step of sequentially mesa-etching the n type upper ohmic contact layer, the tunnel junction layer, and the active layer such that the lower ohmic contact layer is exposed; and a sixth step of simultaneously forming an n type ohmic contact metal electrode layer which is ohmic-contacted with the n type upper ohmic contact layer and the n type lower ohmic contact layer at selected regions on the n type upper ohmic contact layer and the n type lower ohmic contact layer.
Brief Description of the Drawings
Figs, la through lj are sectional views for describing a conventional method of manufacturing a nitride semiconductor light emitting device;
Fig. 2 is a sectional view for describing a nitride semiconductor light emitting device in accordance with a first embodiment of the present invention; Figs. 3a through 3e are sectional views for describing a manufacturing method of the nitride semiconductor light emitting device of Fig. 2;
Figs .4 and 5 are sectional views for describing a nitride semiconductor light emitting device in accordance with a second embodiment of the invention;
Fig. 6 is a sectional view for describing a nitride semiconductor light emitting device in accordance with a third embodiment of the invention; and
Fig. 7 is a sectional view for describing a nitride semiconductor light emitting device in accordance with a fourth embodiment of the invention.
Best Mode for Carrying Out the Invention
Hereinafter, there are in detail described preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, like elements having the same function are designated by identical reference numerals, and their repeated descriptions are intentionally omitted.
[Embodiment 1]
Fig. 2 is a sectional view for illustrating a nitride semiconductor light emitting device grown by a MOCVD (Metalorganic Chemical Vapor Deposition) in accordance with a first embodiment of the invention. In Fig. 2, superscript symbols "++", "+", "- attached adjacent to the conductivity type letters p" or "n", represent relative doping concentrations. As it travels in the order of "++", "+", "-", doping concentration becomes low. Referring to Fig. 2, on a substrate 11 is formed a buffer layer 21 made of GaN. As the substrate 11, there may be used a sapphire substrate (A1203) has a crystallographic orientation of (0001) c. In addition, a substrate made of SiC, GaAs, ZnO, or MgO can be used. The buffer layer 21 is formed to a thickness of 250 A to 300 A at a temperature of 560 °C and a pressure of 300 torr.
At this time, supply flows of atmospheric gases including TMGa, hydrogen, and ammonia are respectively 70 μmol/min,5.51/min, and 41/min. Hydrogen is used as a carrier gas, and hereinafter its used example description is omitted. In addition to GaN, the buffer layer 21 may be made of A1N, AlGaN, or InGaN .
On the buffer layer 21, there is formed an n+ type lower ohmic contact layer 31 made of Si-doped GaN. The buffer layer
21 serves to make a role in buffering occurrence of microcracks in the n+ type lower ohmic contact layer 31 and layers formed thereon due to the differences of lattice constants and thermal expansion coefficients.
On the n+ type lower ohmic contact layer 31, there is formed an active layer 41 capable of radiating light having a wavelength of 370 nm to 600 nm. The active layer 41 is formed at a temperature of 750 °C, and at this time, a supply flow of used TMGa is 3.74 μmol/min.
The active layer 41 has a double heterostructure of
InGaN\GaN, or may have a single quantum well structure of GaN\InGaN\GaN, or a multiple quantum well structure of
GaN\InGaN\GaN\ \GaN\InGaN\GaN .
On the active layer 41, there is formed a p~type clad layer 53 of Mg-doped GaN and having a thickness of 10 A to
10, 000 A. The p"type clad layer 53 is formed at an approximately 1,130 °C, and at this time, the supply flows of TMGa, ammonia, and Cp2Mg as used, are respectively 112 μmol/min, 41/min, and 1.07 μmol/min. In addition to the GaN, the p-type clad layer 53 may be made of AlxGaι-xN, wherein x is O≤ x≤ 0.5.
On the p~type clad layer 53, there is formed a tunnel junction layer 55. The tunnel junction layer 55 has a structure in which a p++ type GaN layer 51 and an n++ type GaN layer 61 are sequentially stacked and a delta doping layer 57 is sandwiched therebetween.
The delta doping layer 57 is indicative of a layer in which Si is very thinly doped into a surface of the GaN layer. Besides the dopant of Si, n type dopants such as 0, Ge, or Sn may be delta-doped. Also, p type dopants such as Zn, Cd, Mg, or Be may be delta-doped. Occasionally, the delta doping layer 57 may have a stack structure in which an Mg-doped delta doping layer and a Si-doped delta doping layer are sequentially stacked.
Although the present embodiment has been described with one example in which the tunnel junction layer 55 has the stack structure in which the p++ type GaN layer 51 and the n++ type GaN layer 61 are sequentially stacked and the delta doping layer 57 is sandwiched therebetween, it can be modified by another example in which only the n++ type delta doping layer is formed on the p++ type GaN layer 51 without the n++ type GaN layer 61. On the tunnel junction layer 55, there is formed an n~type clad layer 63 to a thickness of 10 A to 10,000 A. Here, the n'type clad layer 63 is comprised of Si-doped GaN, and is formed by respectively supplying TMGa, ammonia, and SiH4 at flow rates of 112 μmol/min, 4 1/min, and 1.72 nmol/min. On the n~type clad layer 63, there is formed an n+ type upper ohmic contact layer 71 made of Si-doped GaN. The n+ type upper ohmic contact layer 71 and the n+ type lower ohmic contact layer 31 are respectively ohmic-contacted with an n type ohmic contact metal electrode. Unlike the conventional structure, the structure of Fig. 2 is further provided with the tunnel junction layer 55. To this end, it allows not the use of the p+ type upper ohmic contact layer but the use of n+ type upper ohmic contact layer 71. Accordingly, an ohmic contact property with the n type ohmic contact metal electrode layer 141 is enhanced and thereby a driving voltage for devices becomes lowered.
The light emission principle in the nitride semiconductor light emitting device of Fig. 2 can be briefly described as follows. If a reverse bias is applied through the n type ohmic contact metal electrode layer 141 to the tunnel junction layer 55, electrons in the valence band of the p++ type GaN layer 51 makes a tunneling into the n++ type GaN layer 61. Accordingly, holes are created at vacant sites where the electrons were transferred in the p++ GaN layer 51. These holes are injected into the active layer 41 via the p~ type clad layer 53. These holes injected into the active layer 41 are recombined with the electrons supplied into the active layer
41 through the n+ type lower ohmic electrode layer 31, so that light is emitted from the active layer 41. Meanwhile, although not shown in the drawings, an n~ type clad layer may be further formed between the n+ type lower ohmic contact layer 31 and the active layer 41.
Figs. 3a through 3e are sectional views for illustrating a method for manufacturing the nitride semiconductor light emitting device of Fig. 2. In Fig. 2, since the buffer layer
21, the p~ type clad layer 53, and the n~ type clad layer 63 are not essential elements, descriptions on methods for manufacturing these layers are intentionally omitted.
Fig. 3a is a sectional view for illustrating steps of forming the n+ type lower ohmic contact layer 31, the active layer 41, the tunnel layer 55, and the n+ type upper ohmic contact layer 71.
First, the sapphire substrate (A1203) having the crystallographic orientation of (0001) c face is heated to a temperature of 1,130 °C, and at the same time TMGa, ammonia, and SiH4 are respectively introduced at flow rates of 150
μmol/min, 4 1/min, and 3.57 nmol/min to form an n type lower ohmic contact layer 31 to a thickness of 3 μm of Si-doped n type GaN on the substrate 11. Next, on the n type lower ohmic contact layer 31, there is an active layer 41 having a multiple quantum well structure in which GaN layer having a thickness ranged from 80 A to 85 A, and InGaN layer having a thickness ranged from 15 A to 20 A are alternatively stacked by six periods . Here, the GaN layer serves as a barrier layer, and the InGaN layer serves as a well layer.
After that, on the active layer 41, there is formed a tunnel junction layer 55 as a characterizing part of the present invention. The tunnel junction layer 55 has a stack structure in which a p++ type GaN layer 51 and an n++ type GaN layer 61 are sequentially stacked. At this time, it is desirous that a delta doping layer 57 is further formed between the p++ type GaN layer 51 and the n++ type GaN layer 61.
The p++ type GaN layer 51 has a thickness ranged from 10 A to 1 , 000 A, and is formed to have an Mg-doped concentration of 1 x 1018 - 1 x 1021crrf3 by introducing TMGa, ammonia, and Cp2Mg at flow rates of 112 μmol/min, 4 1/min, and 2.14 nmol/ in, respectively.
The delta doping layer 57 is formed by growing the p type GaN layer 51, after an elapse of a growth stop time of 1 - 300 seconds, and introducing ammonia at a flow rate of 10 seconds to 30 seconds, and SiH4 at a flow rate of 50.22 nmol/min such that Si is delta-doped into the GaN layer at a planar doping concentration of 1 x 1011 - 1 x 1014 cm-2. After the formation of the delta doping layer 57, the n++ type GaN layer 61 is formed to a thickness ranged from 10 A to 1,000 A by introducing TMGa, ammonia, and SiH4 at flow rates of 112 μmol/min, 4 1/min, and 50.22 nmol/min, respectively such that it has a doping concentration of 1 x 1018 - 1 x 1021 cm"3.
Continuously, the n+ type upper ohmic contact layer 71 having a thickness ranged from 100 A to 5,000 A and made of Si-doped n type GaN is formed by introducing TMGa, ammonia, and SiH4 at flow rates of 112 μmol/min, 4 1/min, and 3.74 nmol/min, respectively. Afterwards, an etch stopper film 111 of Si02 is formed on a selected region of the n+ type upper ohmic contact layer 71.
Fig. 3b is a sectional view for illustrating a mesa etch step. Specifically, a dry etch is carried out by using the etch stopper film as an etch mask using an ICP (Inductively coupled plasma) , to thereby remove the etch stopper film 111.
Figs. 3c through 3e are sectional views for illustrating steps of forming the n type ohmic contact metal electrode layer
141. First, on the entire surface of the resultant structure in which the etch stopper film 111 was removed, there is formed a photosensitive film and is then patterned to form a photosensitive film pattern 121a exposing the n type upper ohmic contact layer 71 and the n type lower ohmic contact layer 31, respectively. Thereafter, on the entire surface of the resultant structure in which the photosensitive film pattern 121a is formed, there is formed the n type ohmic contact electrode layer 141 made of a metal selected from a group consisting of Ti, Al, andAu. Afterwards, the photosensitive film pattern 121a is removed to form the n type ohmic contact metal electrode layer 141 only on the n type upper ohmic contact layer 71 and the n type lower ohmic contact layer 31.
Next, the resultant substrate is thermally annealed at a temperature range of 350 - 1, 000 °C such that the n type ohmic contact metal electrode layer 141 is ohmic-contacted with the n type upper ohmic contact layer 71 and the n type lower ohmic contact layer 31, so that the nitride semiconductor light emitting device is completed.
[Embodiment 2]
Fig. 4 is a sectional view for illustrating a nitride semiconductor light emitting device in accordance with a second embodiment of the present invention. The structure shown in Fig. 4 has a difference from the structure shown in Fig. 2 in that the light emitting part in the structure shown in Fig. 2 is comprised of the active layer 41, the p" type clad layer 53, the tunnel junction layer 55, and the n" type clad layer 63 while a light emitting part in the structure shown in Fig. 4 has a stack structure in which they are alternatively and repeatedly stacked. In Fig. 4, there is shown a stack structure in which they are repeatedly by twice times and stacked. In other words, the light emitting part has a stack structure in which a first active layer 41' , a first p" type clad layer 53' , a first tunnel junction layer 55' , a first n~ type clad layer 63' , a second active layer 41", a second p" type clad layer 53", a second tunnel junction layer 55", and a second n" type clad layer 63" are sequentially stacked.
In the above, the first active layer 41' and the second active layer 41" may emit lights having different wavelengths or light having an identical wavelength. In case that the first active layer 41' and the second active layer 41" emit lights having different wavelengths, it is preferable to allow the first active layer 41' to emit light having a wavelength longer than the second active layer 41" such that a minimum light is absorbed when the light emitted from the first active layer 41' passes through the second active layer 41", thereby allowing all lights having different wavelengths to be emitted. In case that yellow light is emitted from the first active layer 41' and blue light is emitted from the second active layer 41", white light is output on the whole.
In case that the first active layer 41' and the second active layer 41" both emit a light having the same wavelength, the light is dually output and thereby light emission efficiency is increased. This increase in the light emission efficiency becomes larger as the region of a depletion layer is smaller, the barrier height is lower, and the interface of tunnel junction is more abruptly formed in the first tunnel junction layer 55' and the second tunnel junction layer 55" respectively such that a tunneling occurs with ease. This is because as the interface of tunnel junction is formed more abruptly, less the lights generated from the first and second active layers 41' and 41" are lost. An increase in such the light emission efficiency occurs more largely due to the existence of the delta doping layers 57' and 57".
Thus, in case that the multiple active layers 41' and 41" are formed, there are advantages in that an input of a single electric power allows a combination of two colors or more, and an acquisition of a high luminance irradiation having a single wavelength. According to the conventional structure, it is impossible to realize the light emitting device having the multiple active layers.
The clad layer is not the essential element. In Fig. 5, there is shown a structure in which active layer and tunnel junction layer is three times repeatedly stacked.
[Embodiment 3]
Fig. 6 is a sectional view for illustrating a nitride semiconductor light emitting device in accordance with a third embodiment of the present invention. Referring to Fig. 6, the device is characterized in that a tunnel junction layer 55 has a stack structure in which a p type GaN layer 51 and an n type GaN layer 61 are sequentially stacked, and is interposed between two active layers 41' and 41". Also, unlike the aforementioned embodiments 1 and 2, the device of the present embodiment is characterized in that a p type ohmic contact metal electrode layer 142 is used instead of the n type ohmic contact metal electrode layer 141.
A light emitting part has a stack structure in which the first active layer 41', a p~ type clad layer 53, the tunnel junction layer, and the second active layer 41" are sequentially stacked. Here, the p" type clad layer 53 may be omitted.
Since the p+ type upper ohmic contact layer 72 instead of the n+ type upper ohmic contact layer 71 should be formed on the second active layer 41", ohmic contact characteristic is not enhanced. However, unlike the conventional art, since the tunnel junction layer 55 is introduced and thereby the multiple active layers are formed, there are advantages in that an input of a single electric power allows a combination of two colors or more, and an acquisition of a high luminance irradiation having a single wavelength like the second embodiment .
[Embodiment 4] Fig. 7 is a sectional view for illustrating a nitride semiconductor light emitting device in accordance with a fourth embodiment of the present invention. The device of Fig. 7 is basically the same as that of Fig. 2, but there is a difference in that an active layer 41 is placed on a tunnel junction layer 55' . Another difference is that the tunnel junction layer 55' has a stack structure in which an n++ type GaN layer 61 and a p++ type GaN layer 51 are sequentially stacked, and a delta doping layer 57 is interposed therebetween. Although the nitride semiconductor light emitting device realized by the single active layer 41 is shown in Fig. 7, it is apparent that a light emitting device realized by multiple active layers can be manufactured as mentioned in the second and third embodiments.
Industrial Applicability As described previously, the nitride semiconductor light emitting devices according to the present invention, introduces tunnel junction layers 55, 55',... so that it becomes possible to form the upper ohmic contact layer 71 using the n+ type GaN layer. So, unlike the conventional case which uses the p type ohmic contact metal electrode layer for the ohmic contact with the p type upper ohmic contact layer, the present invention uses the n type ohmic contact metal electrode layer 141 for the ohmic contact with the n type upper ohmic contact layer 71. Accordingly, the ohmic contact characteristic with metal is enhanced in comparison with the conventional case, thus the conductivity and the current spreading is increased, and thereby the light emission efficiency of the device is enhanced and the driving voltage is lowered.
Also, unlike the conventional art, the n type ohmic contact metal layer 141 which is ohmic-contacted with the n type upper ohmic contact layer 71 and the n type lower ohmic contact layer 31 respectively can be formed by once lift-off process and once thermal annealing process for ohmic contact. To this end, its manufacturing process is very simple and rapid.
Further, since the n type upper ohmic contact layer 71 is made of n type nitride semiconductor, it has a very good conductivity compared with the conventional case. Accordingly, there is no need to form the p type ohmic contact electrode layer 130 on the entire surface of the p type upper ohmic contact layer 80 and form the p type bonding electrode layer 150 on the p type semitransparent ohmic contact electrode layer 130 like the conventional case, but there is a need to form only the n type ohmic contact metal electrode layer 141 on a selected region of the n type upper ohmic contact layer 71, so that current uniformly flows through the entire surface of the n type upper ohmic contact layer 71. Accordingly, there is no light absorption by the semitransparent p type ohmic contact electrode layer 130 shown in .the conventional art, so that high luminance irradiation occurs laterally and upwardly from the device. Furthermore, according to the present invention, the introduction of the tunnel junction layers 55, 55', ... allows to formmultiple active layers 41, 41' , .... Accordingly, when it is necessary that the active layers 41, 41' , ... emit lights having different wavelengths, lights having different wavelengths can be simultaneously emitted using a single driving voltage, and thereby it becomes possible to emit white light .
Moreover, even when it is necessary that the active layers 41, 41' , ... emit lights having an identical wavelength, a light emission effect with a high luminance can be obtained using a single driving voltage. The increase in the irradiation effect appears more largely due to the existence of the delta doping layers 57, 57' , ....
While the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that various modifications and substitutions can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims.

Claims

Claims :
1. A nitride semiconductor light emitting device comprising: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; an active layer formed on the lower ohmic contact layer and made of a nitride semiconductor; a tunnel junction layer formed on the active layer and having a structure in which a p type nitride semiconductor layer and an n type nitride semiconductor layer each of which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm"3 are sequentially stacked; an upper ohmic contact layer formed on the tunnel junction layer and made of the n type nitride semiconductor layer; and an n type ohmic contact metal electrode layer which is ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layers being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer.
2. A nitride semiconductor light emitting device comprising: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; a light emitting part formed on the lower ohmic contact layer and having a structure in which an active layer and a tunnel junction layer are sequentially and repeatedly stacked, the active layer being made of a nitride semiconductor, the tunnel junction layer having a structure in which an n-type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm"3 is stacked on a p-type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm"3; an upper ohmic contact layer formed on the light emitting part and made of n type nitride semiconductor; and an n type ohmic contact metal electrode layer which is ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layers being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer.
3. A nitride semiconductor light emitting device comprising: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; multiple active layers formed on the lower ohmic contact layer and made of a nitride semiconductor; a tunnel junction layer interposed between the multiple active layers and having a structure in which a p type nitride semiconductor layer and an n type nitride semiconductor layer each of which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm"3 are sequentially stacked; an upper ohmic contact layer formed on an uppermost active layer out of the multiple active layers and made of a p type nitride semiconductor; and an n type ohmic contact metal electrode layer and a p type ohmic contact metal electrode which are respectively ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layer and the p type ohmic contact metal electrode layer being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer.
4. A nitride semiconductor light emitting device comprising: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; a tunnel junction layer formed on the lower ohmic contact layer and having a structure in which an n type nitride semiconductor layer and a p type nitride semiconductor layer each of which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm"3 are sequentially stacked; an active layer formed on the tunnel junction layer and made of a nitride semiconductor; an upper ohmic contact layer formed on the active layer and made of n type nitride semiconductor; and an n type ohmic contact metal electrode layer which is ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layers being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer.
5. A nitride semiconductor light emitting device comprising: a lower ohmic contact layer formed on a substrate and made of n type nitride semiconductor; a light emitting part formed on the lower ohmic contact layer and having a structure in which a tunnel junction layer and an active layer are sequentially and repeatedly stacked, the tunnel junction layer having a structure in which a p type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm"3 is stacked on an n type nitride semiconductor layer which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm"3, and the active layer being made of a nitride semiconductor; an upper ohmic contact layer formed on the light emitting part and made of n-type nitride semiconductor; and an n type ohmic contact metal electrode layer which is ohmic-contacted with the lower ohmic contact layer and the upper ohmic contact layer, the n type ohmic contact metal electrode layers being respectively provided on the lower ohmic contact layer and the upper ohmic contact layer.
6. The nitride semiconductor light emitting device of claim 1, further comprising a delta doping layer interposed between the p type nitride semiconductor layer of the tunnel junction layer and the n type nitride semiconductor layer of the tunnel junction layer.
7. The nitride semiconductor light emitting device of claim 2, further comprising a delta doping layer interposed between the p type nitride semiconductor layer of the tunnel junction layer and the n type nitride semiconductor layer of the tunnel junction layer.
8. The nitride semiconductor light emitting device of claim 3, further comprising a delta doping layer interposed between the p type nitride semiconductor layer of the tunnel junction layer and the n type nitride semiconductor layer of the tunnel junction layer.
9. The nitride semiconductor light emitting device of claim 4, further comprising a delta doping layer interposed between the p type nitride semiconductor layer of the tunnel junction layer and the n type nitride semiconductor layer of the tunnel junction layer.
10. The nitride semiconductor light emitting device of claim 5, further comprising a delta doping layer interposed between the p type nitride semiconductor layer of the tunnel junction layer and the n type nitride semiconductor layer of the tunnel junction layer.
11. The nitride semiconductor light emitting device of claim 6, wherein the delta doping layer is formed by delta-doping Si in a planar concentration of 1 x 1011 - 1 x 10" cm"2.
12. The nitride semiconductor light emitting device of claim 7, wherein wherein the delta doping layer is formed by delta-doping Si in a planar concentration of 1 x 1011 - 1 x 1014 cm"2.
13. The nitride semiconductor light emitting device of claim 8, wherein wherein the delta doping layer is formed by delta-doping Si in a planar concentration of 1 x 1011 - 1 x 10 cm .
14. The nitride semiconductor light emitting device of claim 9, wherein wherein the delta doping layer is formed by delta-doping Si in a planar concentration of 1 x 1011 - 1 x 1014 cm"2.
15. The nitride semiconductor light emitting device of claim 10, wherein wherein the delta doping layer is formed by delta-doping Si in a planar concentration of 1 x 1011 - 1 x 1014 cm"2,
16. The nitride semiconductor light emitting device of claim 11, wherein wherein the delta doping layer is formed by delta-doping Si in a planar concentration of 1 x 1011 - 1 x 1014 cm"2.
17. A method for manufacturing a nitride semiconductor light emitting device, the method comprising: a first step of forming an n type lower ohmic contact layer made of n type nitride semiconductor on a substrate; a second step of forming an active layer made of nitride semiconductor on the n type lower ohmic contact layer; a third step of forming a tunnel junction layer on the active layer, the tunnel junction layer having a structure in which a p type nitride semiconductor layer and an n type nitride semiconductor layer are sequentially stacked; a fourth step of forming an n type upper ohmic contact layer made of n type nitride semiconductor on the tunnel junction layer; a fifth step of sequentially mesa-etching the n type upper ohmic contact layer, the tunnel junction layer, and the active layer such that the lower ohmic contact layer is exposed; and a sixth step of simultaneously forming an n type ohmic contact metal electrode layer which is ohmic-contacted with the n type upper ohmic contact layer and the n type lower ohmic contact layer at selected regions on the n type upper ohmic contact layer and the n type lower ohmic contact layer.
18. A nitride semiconductor light emitting device comprising: an active layer made of a nitride semiconductor and irradiating light; and a tunnel junction layer formed by a junction of a p type nitride semiconductor layer and an n type nitride semiconductor layer each of which is doped with dopants having a concentration of 1 x 1018 - 1 x 1021 cm"3.
PCT/KR2001/001530 2000-09-14 2001-09-11 Nitride compound semiconductor light emitting device having a tunnel junction structure and fabrication method thereof WO2002023640A1 (en)

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KR20000053982A KR100380536B1 (en) 2000-09-14 2000-09-14 III-Nitride compound semiconductor light emitting device having a tunnel junction structure
KR2000/53982 2000-09-14
KR10-2000-0066637A KR100395660B1 (en) 2000-11-10 2000-11-10 Method for fabricating nitride compound semiconductor light emitting device having tunnel junction layer
KR2000/66637 2000-11-10
KR2000/68925 2000-11-20
KR10-2000-0068925A KR100384597B1 (en) 2000-11-20 2000-11-20 Method of fabricating Tunnel junction layer

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