JP2000091631A - Gallium nitride-based compound semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the light emitting efficiency of a gallium nitride-based compound semiconductor element by putting a light emitting layer between a p-type layer and an n-type layer and setting the ratio of the hole density in the p-type layer to the electron density in the n-type layer within a specified range. SOLUTION: On a substrate 11, a buffer layer 12 is formed. Thereon, an n-type contact layer 13 is formed. Then, a stress relaxing layer 14A is formed on the n-type contact layer 13. On the stress relaxing layer 14A, an n-type clad layer 14B is formed. Then, a light emitting layer 15 of the multiple quantum well structure made by alternately depositing a barrier layer 151 and a well layer 152 is formed on the n-type clad layer 14B. Thereafter, a p-type clad layer 16 is formed on the light emitting layer 15 and then a p-type contact layer 17 is formed on the p-type clad layer 16. In this case, the ratio of the hole density in the p-type clad layer 16 to the electron density in the n-type clad layer 14B is set between 0.5 and 2.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride-based compound semiconductor light emitting device with improved light emission efficiency.
The present invention is particularly effective for a gallium nitride compound semiconductor device emitting ultraviolet light.

[0002]

2. Description of the Related Art The following is a typical example of a light emitting device in which a layer made of a gallium nitride compound semiconductor is laminated on a substrate. That is, a sapphire substrate is used as a substrate, and a buffer layer made of aluminum nitride (AlN), a high carrier concentration n-cladding and n-contact layer made of silicon (Si) -doped GaN as an n-type layer,
A light emitting layer having a multiple quantum well (MQW) structure in which barrier layers made of N and well layers made of InGaN are alternately stacked, a p-type layer made of a magnesium (Mg) -doped AlGaN p-cladding layer, and a p-type layer. Magnesium (Mg) doped Ga as the mold layer
It is known that p contact layers made of N are sequentially laminated. As an ultraviolet light emitting device using a gallium nitride compound semiconductor, one using InGaN or AlGaN for a light emitting layer is known. When InGaN is used for the light emitting layer, when the composition ratio of In is 5.5% or less,
Ultraviolet light of 380 nm or less has been obtained. In addition, Al
When GaN is used, the composition ratio of Al is
By adding (Zn) and silicon (Si), ultraviolet light having a wavelength of 380 nm is obtained by donor-acceptor pair emission.

[0003]

However, the reported gallium nitride-based compound semiconductor light emitting device is not necessarily optimized, and has a problem that the luminous efficiency is still low.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to improve the luminous efficiency of a gallium nitride-based compound semiconductor device.

A first means for solving the above-mentioned problem is a double heterojunction gallium nitride-based compound semiconductor light-emitting device having a light-emitting layer sandwiched between a p-type layer and an n-type layer.
The ratio of the hole concentration in the mold layer to the electron concentration in the n-type layer is 0.5
More than 2.0. The second means is:
Similarly to the above, the ratio of the concentration of holes in the p-type layer to the concentration of electrons in the n-type layer is set to 0.7 or more and 1.43 or less. A third means is to set the ratio of the concentration of holes in the p-type layer to the concentration of electrons in the n-type layer to be 0.8 or more and 1.25 or less in the same manner as described above. Further, a fourth means is to design the emission wavelength to be in the ultraviolet range. With these means, the above-mentioned problems can be solved.

[0006]

In the double heterojunction gallium nitride compound semiconductor light emitting device, the formation of the n-type layer is easier than the formation of the p-type layer, and the concentration of holes in the p-type layer is n-type. The electron concentration of the layer was lower than the electron concentration. The n-cladding layer and the p-type layer (p-cladding layer and p-contact layer) and the electron concentration of the n-type layer (n-cladding layer and n-contact layer) are brought close to 1 so that the ratio of the concentration of holes in the p-type layer (p-cladding layer and p-contact layer) is close to 1. FIGS. 2 and 3 show the results of changing the electron concentration of the n-contact layer. The hole concentrations of the p-cladding layer and the p-contact layer are 2 × 10 ¹⁷ / cm ³ and 7 × 10 ¹⁷ / cm ³ . The emission intensity of this light emitting device has a strong correlation with the electron concentration of the n cladding layer made of Al _0.05 Ga _0.95 N. Al _0.05 Ga
FIG. 2 is a graph showing the results obtained by preparing a large number of samples having different electron concentrations of the n-cladding layer of _0.95 N and measuring the emission intensity by electroluminescence (EL).
As can be seen from this figure, the emission intensity of the light emitting element is
The electron concentration of the n-cladding layer has a peak around 8 × 10 ¹⁷ / cm ³ . On the other hand, the light emission intensity of this light emitting element is Ga
It also has a strong correlation with the electron concentration of the n contact layer made of N. FIG. 3 is a graph showing the results obtained by preparing a large number of samples of the GaN n-contact layer having different electron concentrations and measuring the luminescence intensity by EL. As you can see from this figure,
The emission intensity of the above light emitting element is such that the n contact layer made of GaN is 1.1 × 10 ¹⁸ / cm ³ , 8 × 10 ¹⁷ / cm ³ , 4 × 10 ¹⁷ / cm ³
As the electron concentration decreases, the emission intensity increases. These results can be explained assuming that recombination of electrons and holes has started to occur in the central part of the light emitting layer. That is, when the electron concentration of the n-cladding layer and the n-contact layer is higher than the hole concentration of the p-cladding layer and the p-contact layer, electrons move from the center of the light emitting layer toward the p-contact layer (p-cladding layer). Assuming that the non-radiative recombination of electrons and holes increases, the concentration of the holes in the p-cladding layer and the p-contact layer, the n-cladding layer, It can be understood that the concentration of electrons in the n-contact layer should be balanced. However, in order to drive electrons by injecting electrons through the electrodes, the electron concentration of the n-contact layer made of GaN must be at least 1 × 10 ¹⁷
/ cm ³ is required.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific embodiments. FIG. 1 shows a light emitting device 10 made of a GaN-based compound semiconductor formed on a sapphire substrate 11.
FIG. 2 is a schematic cross-sectional configuration diagram of No. 0. On the substrate 11, a buffer layer 1 of aluminum nitride (AlN) having a thickness of about 25 nm
2, an n-contact layer 13 made of silicon (Si) doped GaN and having a thickness of about 3000 nm is formed thereon. Non-doped In _0.03 is formed on the n-contact layer 13.
A strain relaxation layer 14A of Ga _0.87 N having a thickness of about 180 nm is formed. The strain relieving layer 14A is for relieving the stress applied to the light emitting layer 15 caused by the difference in the thermal expansion coefficient between the sapphire substrate 11 and the light emitting layer 15.
An n-cladding layer 1 of silicon (Si) -doped Al _0.05 Ga _0.5 N having a thickness of about 200 nm is formed on the strain relaxation layer 14A.
4B is formed.

Then, a film having a thickness of about
A light emitting layer 15 having a multiple quantum well (MQW) structure in which barrier layers 151 made of 3.5 nm Al _0.13 Ga _0.87 N and well layers 152 made of In _0.05 Ga _0.95 N having a thickness of about 3 nm are alternately formed. ing. The barrier layer 151 has six layers, and the well layer 152 has five layers. On the light emitting layer 15, a p-cladding layer 16 of p-type Al _0.15 Ga _0.85 N having a thickness of about 25 nm is formed. Further, a p-contact layer 17 of p-type GaN having a thickness of about 100 nm is formed on the p-cladding layer 16.

A transparent electrode 18A is formed on the p-contact layer 17 by metal evaporation, and an electrode 18B is formed on the n-contact layer 13. Translucent electrode 18A
Is made of cobalt (Co) having a thickness of about 1.5 nm bonded to the p-contact layer 17 and gold (Au) having a thickness of about 6 nm bonded to Co. The electrode 18B is made of vanadium (V) having a thickness of about 20 nm.
And an aluminum (Al) or Al alloy having a thickness of about 1800 nm. A part of the electrode 18A has a film thickness of about 1500 made of Co or Ni or V and Au, Al, or an alloy thereof.
An nm electrode pad 20 is formed.

Next, a method for manufacturing the light emitting device 100 will be described. The light emitting device 100 was manufactured by vapor phase growth by metal organic chemical vapor deposition (hereinafter abbreviated as “MOVPE”). The gases used were ammonia (NH ₃ ), carrier gas (H ₂ , N ₂ ), trimethylgallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), and trimethylaluminum (Al (CH ₃ )).
₃ ) (hereinafter referred to as “TMA”), trimethylindium (In
(CH ₃ ) ₃ ) (hereinafter referred to as “TMI”), silane (SiH ₄ ) and cyclopentadienyl magnesium (Mg (C ₅ H ₅ ) ₂ ) (hereinafter “CP
₂ Mg ”). First, a single crystal substrate 11 having an a-plane as a main surface, which has been cleaned by organic cleaning and heat treatment, is subjected to MOVPE.
The susceptor is mounted on the reaction chamber of the apparatus. next,
The substrate 11 was baked at a temperature of 1100 ° C. while flowing H ₂ into the reaction chamber at normal pressure. Next, the temperature of the substrate 11 was lowered to 400 ° C., and H ₂ , NH ₃ and TMA were supplied to form the AlN buffer layer 12 to a thickness of about 25 nm.

Next, the temperature of the substrate 11 is maintained at 1150 ° C.
Supplying H ₂ , NH ₃ , TMG and silane, the film thickness is about 3000 nm, n
An n-contact layer 13 made of type GaN was formed. next,
By lowering the temperature of the substrate 11 to 850 ° C., N ₂ or H ₂ ,
By supplying NH ₃ , TMG and TMI, a strain relaxation layer 14A made of non-doped In _0.03 Ga _0.97 N and having a thickness of about 180 nm was formed. After the formation of the strain relaxation layer 14A, the temperature of the substrate 11 is raised again to 1150 ° C., and N ₂ or H ₂ , NH ₃ , TM
G, by supplying TMA and silane, to form an n-clad layer 14B having a thickness of 200nm composed of n-type Al _0.05 Ga _0.95 N.

Next, N ₂ or H ₂ , NH ₃ , TMG and TMA were supplied to form a barrier layer 151 of Al _0.13 Ga _0.87 N having a thickness of about 3.5 nm. Then, N ₂ or H _2, NH _3, TMG and
By supplying TMI, a well layer 152 of In _0.05 Ga _0.95 N having a thickness of about 3 nm was formed. Further, four periods of the barrier layer 151 and the well layer 152 are formed under the same conditions, and an Al _0.13 Ga
_A barrier layer 151 of _0.87 N was formed. Thus, the light emitting layer 15 having the MQW structure was formed.

Next, the temperature of the substrate 11 is maintained at 1150 ° C.
Supplying N ₂ or H ₂ , NH ₃ , TMG, TMA and CP ₂ Mg, a film thickness of about 25 nm, p-type Al _0.15 Ga doped with magnesium (Mg)
_A p-cladding layer 16 of _0.85 N was formed. Next, the temperature of the substrate 11 is maintained at 1100 ° C., and N ₂ or H ₂ , NH ₃ , TMG
Then, by supplying CP ₂ Mg, a p-contact layer 17 made of p-type GaN doped with Mg and having a thickness of about 100 nm was formed. Next, an etching mask is formed on the p-contact layer 17, the mask in a predetermined region is removed, and portions of the p-contact layer 17, the p-cladding layer 16, the light-emitting layer 15, and the strain relief layer which are not covered with the mask are removed. 14. A part of the n-contact layer 13 was etched by reactive ion etching using a gas containing chlorine to expose the surface of the n-contact layer 13. Next, an electrode 18B for the n-contact layer 13 and a translucent electrode 18A for the p-contact layer 17 were formed by the following procedure.

(1) A photoresist is applied, a window is formed in a predetermined region on the exposed surface of the n-contact layer 13 by photolithography, and the window is evacuated to a high vacuum of the order of 10 ⁻⁶ Torr or less. 20 nm vanadium (V) and a film thickness of about 1800 nm
Al was deposited. Next, the photoresist is removed. As a result, the electrode 18B is formed on the exposed surface of the n-contact layer 13. (2) Next, apply photoresist uniformly on the surface,
By photolithography, the photoresist on the electrode formation portion on the p-contact layer 17 is removed to form a window. (3) After evacuation to a high vacuum of the order of 10 ⁻⁶ Torr or less on the photoresist and the exposed p-contact layer 17 using a vapor deposition apparatus, a Co film having a thickness of about 1.5 nm is formed. Then, a film of Au having a thickness of about 6 nm is formed.

(4) Next, the sample is taken out of the vapor deposition device,
Co, Au deposited on photoresist by lift-off method
Is removed, and a transparent electrode 18A is formed on the p-contact layer 17.
To form (5) Next, in order to form a bonding electrode pad 20 on a part of the translucent electrode 18A, a photoresist is uniformly applied, and a photoresist is applied to a portion of the electrode pad 20 where the photoresist is formed. Open the window. Next, Co or Ni or V
And Au, Al, or an alloy thereof to a film thickness of about 1500 nm by vapor deposition, and in the same manner as in the step (4), Co or Ni or V and Au, deposited on the photoresist by a lift-off method. The electrode pad 20 is formed by removing the film made of Al or an alloy thereof. (6) Thereafter, the sample atmosphere is evacuated with a vacuum pump, and O ₂ gas is supplied to a pressure of 3 Pa.
Heat to about 50 ° C for about 3 minutes to make p contact layer 17,
The p-cladding layer 16 was reduced in p-type resistance and alloyed between the p-contact layer 17 and the electrode 18A and alloyed between the n-contact layer 13 and the electrode 18B. Thus, the light emitting element 100 was formed.

A number of samples having different electron concentrations of the n-cladding layer 14B made of n-type Al _0.05 Ga _0.95 N were prepared, and their ELs were prepared.
FIG. 2 is a graph showing the results of measuring the light emission intensity by the method. As can be seen from this figure, the light emission intensity of the light emitting element 100 shows a high luminous intensity when the electron concentration of the n cladding layer is around 8 × 10 ¹⁷ / cm ³ . Also, an n-contact layer 1 made of n-type GaN
FIG. 3 is a graph showing the results of preparing a large number of samples having different electron densities and measuring the luminescence intensity by EL.
As can be seen from this figure, the emission intensity of the light emitting element 100 is:
The electron concentration of the n-contact layer is 1.1 × 10 ¹⁸ / cm ³ , 8 × 10
Luminous intensity becomes larger as as low as ^{17 / cm 3, 4 × 10} 17 / cm 3. In each case, since the electron concentration of the p-type layer (p-cladding layer and p-contact layer) is 7 × 10 ¹⁷ / cm ³ , the ratio of the concentration of holes in the p-type layer to the concentration of electrons in the n-type layer. However, the effect is recognized in the range of 0.5 or more and 2.0 or less. Preferably, the ratio of the concentration of holes in the p-type layer to the concentration of electrons in the n-type layer is 0.7 or more and 1.43 or less, more preferably 0.8 or more and 1.25 or less.

In the above embodiment, the light emitting device 100
Although the light emitting layer 15 has a multiple quantum well structure, the light emitting layer may have a single quantum well structure. Further, as long as the ratio of the concentration of holes in the p-type layer to the concentration of electrons in the n-type layer is as described in the present invention, the barrier layer, the well layer, the n and p cladding layers, and the n and p contact layers are optional. Quaternary ratio of 3 and 3
, Binary Al _X Ga _1-XY In _Y N (0 ≦ X ≦ 1,0 ≦ Y
≤ 1). In addition, although the effect is reduced without the n-cladding layer and the strain relaxation layer, the output is larger than that of the conventional light emitting element without it. Although Mg is used as the p-type impurity, a Group 2 element such as beryllium (Be) and zinc (Zn) can be used. Further, the present invention can be used not only for light emitting elements but also for light receiving elements.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a GaN-based compound semiconductor light emitting device 100 according to a specific embodiment of the present invention.

FIG. 2 is a graph showing the correlation between the electron concentration of an n-cladding layer and the emission intensity.

FIG. 3 is a graph showing the correlation between the electron concentration of an n-contact layer and the emission intensity.

[Explanation of symbols]

 Reference Signs List 11 sapphire substrate 12 buffer layer 13 n contact layer 14A strain relaxation layer 14B n clad layer 15 light emitting layer 151 barrier layer 152 well layer 16 p clad layer 17 p contact layer 18A p electrode 18B n electrode 20 electrode pad 100 light emitting element

 ──────────────────────────────────────────────────の Continuing on the front page (72) Norikatsu Koide, No. 1, Nagahata, Ochiai, Kasuga-cho, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. 1 address F-term (reference) in Toyoda Gosei Co., Ltd. 5F041 AA03 CA03 CA04 CA05 CA12 CA34 CA49 CA53 CA57 CA64 CA67 CA82 CA84 CA88 CB06

Claims (4)

[Claims] 1. A double heterojunction gallium nitride-based compound semiconductor light-emitting device having a light-emitting layer sandwiched between a p-type layer and an n-type layer, wherein the concentration of holes in the p-type layer and the concentration of electrons in the n-type layer are reduced. A gallium nitride-based compound semiconductor light-emitting device having a ratio of 0.5 or more and 2.0 or less. 2. A double heterojunction gallium nitride-based compound semiconductor light-emitting device having a light-emitting layer sandwiched between a p-type layer and an n-type layer, wherein the concentration of holes in the p-type layer and the concentration of electrons in the n-type layer are different. A gallium nitride based compound semiconductor light emitting device having a ratio of 0.7 or more and 1.43 or less. 3. A double heterojunction gallium nitride-based compound semiconductor light-emitting device having a light-emitting layer sandwiched between a p-type layer and an n-type layer, wherein the concentration of holes in the p-type layer and the concentration of electrons in the n-type layer are different. A gallium nitride based compound semiconductor light emitting device having a ratio of 0.8 or more and 1.25 or less. 4. The method according to claim 1, wherein the emission wavelength is in an ultraviolet region.
The gallium nitride-based compound semiconductor light-emitting device according to claim 1.