JPH11233821A - Gallium nitride compound semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting device of high luminous intensity by a method wherein a mutual relation between the thickness of a P clad layer and the luminous intensity of a gallium nitride compound semiconductor device is made clear. SOLUTION: Gallium nitride compound semiconductor layers are laminated on a substrate for the formation of a light emitting device, wherein a P-type Alx Ga1-x N clad layer (0<=x<1) is set as thick as 90 to 500 Å. First, the reason why the thickness is set above 90 Åis that carrier can not be trapped in an active layer if the thickness is below 90 Å. Second, the reason why the thickness is set below 500 Å is that strong stress is imposed on the active layer if the thickness is above 500 Å, because the active layer and the P-clad layer are different from each other in lattice constant. Or, dislocations are generated in the P-type clad layer due to lattice mismatching, so that the P-clad layer and a P contact layer can not be well improved in crystal structure as desired.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride compound semiconductor device having a high luminous output.

[0002]

2. Description of the Related Art A light emitting device having a double hetero structure emitting green or blue light is known as a light emitting device in which a layer made of a gallium nitride compound semiconductor is laminated on a substrate. The thickness of the p-cladding layer is as thick as 700 °, and further improvement in light emission output has been desired.

[0003]

Conventionally, the luminous intensity of these light-emitting elements has been reduced to p-type doped Al _x Ga ₁ -xN.
Since it was not known to have a strong correlation with the thickness of the p-cladding layer composed of (0 ≦ x <1), a semiconductor light emitting device having a suitable or optimal p-cladding layer thickness for realizing high luminous intensity It was not easy to get.

The present invention has been made to solve the above problems, and an object of the present invention is to clarify the correlation between the thickness of a p-cladding layer and the luminous intensity in a gallium nitride-based compound semiconductor device. Accordingly, it is an object of the present invention to provide a light emitting element with high luminous intensity.

[0005]

Means for solving the above problems are as follows. In a light emitting device in which a layer made of a gallium nitride-based compound semiconductor is laminated on a substrate, a p-type doped Al _x Ga _1- the thickness of the _{x N (0 ≦ x <1} ) than made p-cladding layer is to be less than 500Å than 90 Å.

[0006]

Functions and Effects of the Invention A number of gallium nitride-based compound semiconductor devices having different p-cladding layer thicknesses are experimentally manufactured, and graphs obtained by measuring the light emission output are shown in FIGS. As can be seen from these figures, the luminous intensity of the gallium nitride-based compound semiconductor device largely depends on the thickness of the p-cladding layer. A light emitting element that outputs light of green or blue wavelength,
The reason why the luminous intensity is high when the thickness of the p-cladding layer is 90 ° to 500 ° is firstly that if the thickness is smaller than this range, the carrier cannot be confined in the active layer. is there. Second, if the film thickness is larger than this range, strong stress is applied to the active layer because the active layer and the p-cladding layer have different crystal lattice constants. Alternatively, if the thickness of the p-cladding layer is larger than this range, dislocation due to lattice mismatch occurs in the p-cladding layer,
This is because the p-cladding layer and the p-contact layer further laminated on the p-cladding layer cannot be formed into a desirable high-quality crystal structure.

[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. On the substrate 11, a buffer layer 1 of aluminum nitride (AlN) having a thickness of about 25 nm
2 is provided thereon, and a high carrier concentration n ⁺ layer 13 of silicon (Si) doped GaN having a thickness of about 4.0 μm is formed thereon. On this high carrier concentration n ⁺ layer 13, a film thickness of about 3000 made of non-doped In _x Ga _{1 -X} N (0 <x <1)
The strain relaxation layer 14 is formed. The strain relieving layer 14 is for relieving stress applied to the light emitting layer 15 caused by a difference in thermal expansion coefficient between the sapphire substrate 11 and the light emitting layer 15. A barrier layer 151 made of GaN having a thickness of about 35 ° and a
The light emitting layer 15 has a multiple quantum well structure (MQW) in which well layers 152 made of Ga _0.8 In _0.2 N are alternately stacked. The barrier layer 151 has six layers, and the well layer 152 has five layers. On the light emitting layer 15, a p-type cladding layer 16 of p-type Al _0.12 Ga _0.88 N having a thickness of about 300 ° is formed. Further, on the p-cladding layer 16, a p-contact layer 17 made of p-type GaN and having a thickness of about 100 nm is formed.

A light-transmissive electrode 18A formed by metal evaporation is formed on the p-contact layer 17, and the electrode 1A is formed on the n ⁺ layer 13.
8B are formed. The light-transmissive electrode 18A is made of cobalt (Co) having a thickness of about 15 ° and joined to the p-contact layer 17,
It is composed of gold (Au) with a film thickness of about 60 ° bonded to Co.
The electrode 18B is made of vanadium (V) having a thickness of about 200
It is composed of 1.8 μm aluminum (Al) or Al alloy. On a part of the electrode 18A, Co or Ni and Au, Al,
Alternatively, an electrode pad 20 made of an alloy thereof and having a thickness of about 1.5 μm 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 4.0 μm,
High carrier concentration n composed of GaN with electron concentration of 2 × 10 ¹⁸ / cm ^3
+ Layer 13 was formed. Next, the temperature of the substrate 11 is set to 850 ° C.
Then, N ₂ or H ₂ , NH ₃ , TMG and TMI were supplied to form a strain relaxation layer 14 made of InGaN having a thickness of about 3000 °. After forming the strain relaxation layer 14, the substrate 11
It raised the temperature to 1150 ° C., N ₂ or H _2, NH ₃ and TMG
To supply a barrier layer 151 of GaN with a thickness of about 35 °.
Was formed. Next, N ₂ or H ₂ , NH ₃ , TMG and TMI are supplied to form a well layer 1 of Ga _0.8 In _0.2 N having a thickness of about 35 °.
52 were formed. Further, the barrier layer 151 and the well layer 15
2 were formed under the same conditions for four periods, and a barrier layer 151 made of GaN was formed thereon. Thus, MQW of 5 cycles
The light emitting layer 15 having the 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, p-type Al doped with magnesium (Mg) with a thickness of about 300 °
_A p-cladding layer 16 made of _0.12 Ga _0.88 N was formed. Next, the temperature of the substrate 11 was maintained at 1100 ° C., and N ₂ or H ₂ , N ₂
By supplying H ₃ , TMG and CP ₂ Mg, a p-contact layer 17 made of Mg-doped p-type GaN 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 ⁺ layer 13 was etched by reactive ion etching using a gas containing chlorine to expose the surface of the n ⁺ layer 13. Next, an electrode 18B for the n ⁺ layer 13 and
A translucent electrode 18A for the p-contact layer 17 was formed.

(1) A photoresist is applied, a window is formed in a predetermined region on the exposed surface of the n ⁺ layer 13 by photolithography, and the window is evacuated to a high vacuum of the order of 10 ⁻⁶ Torr or less.
Vanadium (V) having a thickness of about 200 ° and Al having a thickness of about 1.8 μm were deposited. Next, the photoresist is removed. Thereby, electrode 18B is formed on the exposed surface of n ⁺ 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) On a photoresist and the exposed p-contact layer 17, a vacuum was evacuated to a high vacuum of the order of 10 ⁻⁶ Torr or less, and then a Co film having a thickness of about 15 ° was formed. About film thickness
A 60-mm Au film 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 and Au,
Al or an alloy thereof is deposited to a film thickness of about 1.5 μm by vapor deposition, and Co or Ni and Au, Au deposited on the photoresist by a lift-off method in the same manner as in the step (4).
The electrode pad 20 is formed by removing the film made of l 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 ⁺ layer 13 and the electrode 18B. Thus, the light emitting element 100 was formed.

FIG. 2 is a graph showing the results of measuring a light emission output of a large number of green light-emitting gallium nitride-based compound semiconductor light emitting devices 100 having different thicknesses of the p-cladding layer 16.
Shown in As can be seen from this figure, in the gallium nitride-based compound semiconductor light-emitting device emitting green light having a main wavelength of 510 nm to 530 nm, the p-cladding layer 16 has a relatively high luminous intensity when the film thickness is in the range of 180 ° to 500 °. More preferably, the thickness of the p-cladding layer 16 is from 240 ° to 360 °.
The range of Å is optimal, and the highest emission output can be obtained in this range. FIG. 3 is a graph showing the relationship between the film thickness of the p-cladding layer 16, the main wavelength, and the light emission output in the gallium nitride-based compound semiconductor light emitting device 100 that emits green light. As can be seen from this figure, there is a tendency that the shorter the dominant wavelength, the higher the light emission output tends to be, but in each dominant wavelength range of green light emission of the present embodiment,
By setting the thickness of the p-cladding layer 16 in the range of 200 ° to 360 °, the strongest light output can be obtained. Further, FIG. 4 is a graph showing the results of measuring a luminous output of a large number of blue light-emitting gallium nitride-based compound semiconductor light emitting devices 100 having different thicknesses of the p-cladding layer 16.
As can be seen from this figure, the dominant wavelength is 460 nm to 475.
In the gallium nitride-based compound semiconductor light emitting device that emits green light of nm, the thickness of the p-cladding layer 16 is 90 ° to 390 °.
Shows a relatively high luminous intensity in the range. More preferably, the thickness of the p-cladding layer 16 is optimally in the range of 120 ° to 300 °, and the highest light emission output can be obtained in this range.

The aluminum (Al) composition ratio x of the p-cladding layer 16 made of p _- type doped Al _x Ga ₁ -xN
Is preferably 0.10 to 0.14. If it is less than 0.10, it becomes difficult to confine carriers in the active layer, so that the luminescence output becomes low.If it is more than 0.14, the stress exerted on the active layer becomes large due to the difference in the lattice constant of the crystal, so that the luminescence output becomes large. Lower. Also, p-type doped Al _x Ga
The crystal growth rate of the p-cladding layer 16 of _1-x N is 2
5 ° / min to 30 ° / min is desirable. p cladding layer 1
6 is desirably not less than 25 ° / min because the p-cladding layer 16 has a surface exposed at the start of crystal growth or a barrier layer 151 having a small thickness. This is because the located well layer 152 is unstable in crystal structure at the crystal growth temperature of the p-cladding layer 16 and thus needs to cover the barrier layer 151 within a short time. The reason why the crystal growth rate of the p-cladding layer 16 is desirably 30 ° / min or less is that if the p-cladding layer 16 is grown at a higher rate,
This is because the crystal structure of the cladding layer 16 is less likely to be formed with good quality. In order to realize the composition ratio and crystal growth rate of the p-cladding layer 16 after forming the light-emitting layer 15 of the MQW structure in the above embodiment, the temperature of the substrate 11 was kept at 1000 ° C., N ₂ or H ₂ 70~100L / min, NH
₃ to 10 to 15 L / min, TMG to 50 to 80 μmol / min, T
MA may be supplied at a rate of 7 to 15 μmol / min, and CP ₂ Mg may be supplied at a rate of 0.15 to 0.3 μmol / min.

In the above embodiment, the light emitting device 100
Although the light emitting layer 15 has an MQW structure, the structure of the light emitting layer is as follows.
The SQW structure may be used. The barrier layer, well layer, clad layer, contact layer, and other layers have an arbitrary mixed crystal ratio of 4%.
Ternary, binary, Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1,
0 ≦ y ≦ 1). 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 results of measuring a luminous output of a large number of green light-emitting gallium nitride-based compound semiconductor light emitting devices 100 having different thicknesses of p-cladding layers 16;

FIG. 3 is a graph showing the relationship between the thickness of a p-cladding layer 16 of a gallium nitride-based compound semiconductor light emitting device 100 for emitting green light, the main wavelength, and the light emission output.

FIG. 4 is a graph showing the results of measuring a luminous output of a large number of blue light-emitting gallium nitride-based compound semiconductor light emitting devices 100 having different thicknesses of a p-cladding layer 16;

[Explanation of symbols]

Reference Signs List 11 sapphire substrate 12 buffer layer 13 high carrier concentration n ⁺ layer 14 strain relaxation layer 15 light emitting layer 16 p cladding layer 17 p contact layer 18A p electrode 18B n electrode 20 electrode pad 100 light emitting element

Claims (1)

[Claims] 1. A light-emitting device in which a layer made of a gallium nitride-based compound semiconductor is laminated on a substrate, wherein a p _- cladding layer made of p _- type doped Al _x Ga ₁ -xN (0 ≦ x <1) is provided. A gallium nitride-based compound semiconductor device having a thickness of 90 ° or more and less than 500 °.