JPH10303458A - Gallium nitride compound semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To materialize the wavelength elongation and output increase of a GaN compound semiconductor element. SOLUTION: A buffer layer 11 consisting of AlN, a thermal expansion lightening layer 12 consisting of In0.20 Ga0.80 N, a high carrier concentration n<+> layer 13 consisting of GaN doped with Si, a distorted layer 14 consisting of Al0.15 Ga0.85 N, a light emitting layer 15 of multiple quantum well structure where barrier layers 151 consisting of GaN and well layers 152 consisting of In0.20 Ga0.80 N are stacked alternately, a clad layer 16 consisting of p-type Al0.15 Ga0.85 N, a contact layer 17 consisting of p-type GaN, and an electrode 18A consisting of Co and Au are stacked in order on a sapphire substrate 10. An electrode 18B consisting of V and Al is made on the n<+> layer 13 exposed by etching. The distortion by the difference of lattice constant is given to the light emitting layer 15 by the distorted layer 14, which has a lattice constant different from that of the light emitting layer 15 and is provided under the light emitting layer 15, and the emitted light wavelength is elongated. Moreover, the influence by thermal expansion of a substrate 10 can be removed by providing the thermal expansion lightening layer 12, and it can be made into high output.

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 device capable of increasing the wavelength.

[0002]

2. Description of the Related Art Gallium nitride (GaN) based compound semiconductors are:
It is expected as an element capable of obtaining an emission wavelength in the ultraviolet region to the red region. Conventionally, sapphire is usually used as a substrate in a GaN-based compound semiconductor. However, a difference in thermal expansion coefficient between sapphire and a GaN-based compound semiconductor causes distortion in a semiconductor layer, which adversely affects optical characteristics. For this purpose, for example, in a device in which a buffer layer and a light emitting layer made of AlGaInN are formed on a sapphire substrate,
It is known that layers having different compositions are sequentially laminated to reduce lattice defects of a light emitting layer and improve device characteristics (Japanese Patent Application Laid-Open No. 8-70139).

[0003]

However, in the above prior art, in order to increase the emission wavelength, the composition ratio of In in the light emitting layer is increased. However, the crystallinity is increased due to the increase in the In composition ratio. There is a problem that the light emission is deteriorated and the light emission intensity is significantly reduced.

Accordingly, an object of the present invention is to achieve a longer wavelength and a higher output of a GaN-based compound semiconductor device in view of the above problems.

[0005]

According to a first aspect of the present invention, there is provided a GaN-based compound semiconductor device having a first semiconductor layer having a lattice constant different from that of an active layer. Is provided on the substrate side of the active layer, strain is imparted to the active layer by a lattice constant difference between the active layer and the first semiconductor layer. Therefore, long wavelengths can be obtained without changing the composition ratio of the semiconductor layer. Becomes possible. Further, by providing the second semiconductor layer on the substrate side with respect to the first semiconductor layer to reduce the influence of the strain on the active layer due to the thermal expansion of the substrate, the effect of the thermal expansion of the substrate can be removed. High output can be achieved.

According to the second aspect of the present invention, the first
By configuring the semiconductor layer of Al _X Ga _1-X N (0 <X ≦ 1), strain can be effectively applied to the active layer, and the second semiconductor layer can be formed of In _Y Ga _1-Y N With the configuration of (0 <Y ≦ 1), the influence of the thermal expansion of the substrate can be effectively removed.

[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 10.
FIG. 2 is a schematic cross-sectional configuration diagram of No. 0. A buffer layer 1 of aluminum nitride (AlN) having a thickness of about 25 nm is formed on a substrate 10.
1 on which a film thickness of In _0.20 Ga _0.80 N is formed.
A 200 nm thermal expansion relaxation layer (second semiconductor layer) 12 is formed. On the thermal expansion moderating layer 12, a high carrier concentration n ^{+ of} about 4.0 μm made of GaN doped with silicon (Si) is used.
Layer 13 is formed. This high carrier concentration n ⁺ layer 1
A strain layer (first semiconductor layer) 14 made of Al _0.15 Ga _0.85 N and having a thickness of about 40 nm is formed on 3.

Then, a Ga film having a thickness of about 35 ° is formed on the strained layer 14.
N _0.20 Ga _0.80 with a thickness of about 35 °
A light emitting layer (active layer) 15 having a multiple quantum well structure (MQW) in which well layers 152 made of N 2 are alternately stacked is formed. The barrier layer 151 has six layers, and the well layer 152 has five layers. On the light emitting layer 15, a cladding layer 16 of p-type Al _0.15 Ga _0.85 N with a thickness of about 50 nm is formed. Further, on the cladding layer 16, a film thickness of about 10
A 0 nm contact layer 17 is formed.

A light-transmissive electrode 18A formed by metal evaporation is formed on the contact layer 17, and the electrode 18A is formed on the n ⁺ layer 13.
B is formed. The light-transmissive electrode 18A is made of cobalt (Co) having a thickness of about 40
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 mm and a thickness of about 1.
It is composed of 8 μm aluminum (Al) or Al alloy.

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”), trimethyl aluminum (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 referred to as “CP ₂ Mg”).

First, a single crystal substrate 10 having an a-plane as a main surface cleaned by organic cleaning and heat treatment is mounted on a susceptor placed in a reaction chamber of a MOVPE apparatus. Next, at normal pressure
Temperature while flowing about 30 minutes the reaction chamber of H ₂ at a flow rate of 2 liter / min
The substrate 10 was baked at 1100 ° C.

Next, the temperature is lowered to 400 ° C. to remove H ₂
The buffer layer 11 made of AlN was formed to a thickness of about 25 nm by supplying 20 liter / minute, NH ₃ at 10 liter / minute, and TMA at 1.8 × 10 ⁻⁵ mol / minute. After forming the buffer layer 11, the temperature is set to 600
C., and the supply of N ₂ or H ₂ , NH _{3 was} kept constant, and TMG was supplied at 7.2 × 10 ⁻⁵ mol / min and TMI was supplied at 0.19 × 10 ⁻⁴ mol / min. The thermal expansion relaxation layer 12 made of In _0.20 Ga _0.80 N was formed. Next, the temperature of the substrate 10 was maintained at 1150 ° C., H ₂ was 20 liter / min, and NH ₃ was 10 liter / min.
Min, TMG 1.7 × 10 ^-4 mol / min, 0.86 ppm by H ₂ gas
Silane diluted at 20 × 10 ^-8 mol / min, the film thickness is about 4.0 μm, the electron concentration is 2 × 10 ¹⁸ / cm ³ , and the Si concentration is 4 × 10 ¹⁸ / c
A high carrier concentration n ⁺ layer 13 made of m ³ GaN was formed. Next, the temperature of the substrate 10 is maintained at 1100 ° C., and N ₂ or H ₂
Is supplied at 10 liter / min, NH ₃ at 10 liter / min, TMG at 1.0 × 10 ^-4 mol / min, and TMA at 1.0 × 10 ^-4 mol / min.
A strained layer 14 of 40 nm Al _0.15 Ga _0.85 N was formed.

After the formation of the above-mentioned strained layer 14,
N ₂ or H ₂ 20liter / min and NH ₃ 10liter / min, 2.0 TMG
The barrier layer 151 made of GaN having a film thickness of about 35 ° was formed by supplying at a rate of × 10 ^-4 mol / min. Next, TMG was supplied at a rate of 7.2 × 10 ⁻⁵ mol / min, and TMI was supplied at a constant supply rate of N _2, H ₂ , and NH _3.
Supplied with 0.19 × 10 ^-4 mol / min, a thickness of about 35 Å an In _0.20 Ga
_A well layer 152 of _0.80 N was formed. Further, five periods of the barrier layer 151 and the well layer 152 are formed under the same conditions,
A barrier layer 151 made of GaN was formed thereon. Thus, the light emitting layer 15 having the MQW structure with five periods was formed.

Next, the temperature of the substrate 10 is maintained at 1100 ° C.
N ₂ or H ₂ 10 liter / min, NH ₃ 10 liter / min, TMG 1.0
× 10 ^-4 mol / min, TMA 1.0 × 10 ^-4 mol / min, CP ₂ Mg
Supply at 2 × 10 ^-5 mol / min, film thickness about 50 nm, concentration 5 × 10
¹⁹ / cm ³ magnesium (Mg) doped p-type Al _0.15 Ga
_A cladding layer 16 of _0.85 N was formed.

Next, the temperature of the substrate 10 is maintained at 1100 ° C.
N ₂ or H ₂ 20liter / min and NH ₃ 10liter / min and TMG 1.12
A contact layer made of Mg-doped p-type GaN having a thickness of about 100 nm and a concentration of 5 × 10 ¹⁹ / cm ³ , by supplying CP ₂ Mg at 2 × 10 ^-5 mol / min at × 10 ^-4 mol / min. 17 was formed.

Next, an etching mask is formed on the contact layer 17, a predetermined region of the etching mask is removed, and portions of the contact layer 17, the cladding layer 16, the light emitting layer 15, and the strain which are not covered with the etching mask are removed. Layer 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, with the etching mask left,
A photoresist is applied to the entire surface, and a window is formed in a predetermined region on the exposed surface of the n ⁺ layer 13 by photolithography.
After evacuating to a high vacuum of the order of ^-6 Torr or less, the film thickness is about 200 Å
Of vanadium (V) and Al with a film thickness of about 1.8 μm. Thereafter, by removing the photoresist and the etching mask, the electrode 18B is formed on the exposed surface of the n ⁺ layer 13.

Subsequently, a photoresist is applied on the surface, and the phytoresist of the electrode forming portion on the contact layer 17 is removed by photolithography to form a window, and the contact layer 17 is exposed. Exposed contact layer 1
After evacuating to a high vacuum of the order of 10 ^-6 Torr or less above 7,
Co is deposited to a thickness of about 40 °, and Au is deposited to a thickness of about 60 ° on the Co. Next, the sample is taken out of the vapor deposition apparatus, Co and Au deposited on the photoresist are removed by a lift-off method, and a translucent electrode 18A for the contact layer 17 is formed.

Next, in order to form an electrode pad 20 for bonding on a part of the electrode 18A, a photoresist is uniformly applied, and a window is formed in the photoresist at a portion where the electrode pad 20 is formed. . Next, Co and Au, Al, or an alloy thereof are deposited to a film thickness of about 1.5 μm by vapor deposition, and Co and Au, Al, or an alloy thereof deposited by vapor deposition on a photoresist by a lift-off method. The electrode pad 20 is formed by removing the film made of. Thereafter, the sample atmosphere is evacuated with a vacuum pump, and O ₂ gas is supplied to a pressure of 3 Pa. In this state, the atmosphere temperature is increased to about 550 ° C.
The contact layer 17 and the cladding layer 16 are reduced in p-type resistance by heating for about
And an alloying process between the n ⁺ layer 13 and the electrode 18B. Thus, an electrode 18B for the n ⁺ layer 13 and an electrode 18A for the contact layer 17 were formed.

With the light emitting device 100 having the above-described structure, the characteristic results shown in FIG. 2 were obtained. FIG. 2 shows a comparative example of a conventional structure and a strained layer 14 of the conventional structure.
The characteristic results in the case of adding only are also shown. As shown in FIG. 2, in the conventional structure, the emission wavelength was about 480 nm and the output was about 200 μW. When only the strained layer 14 is added to the conventional structure, the emission wavelength is increased to about 520 nm. In order to increase the emission wavelength, the strained layer 14 is
It is presumed that the light-emitting layer 15 has a lattice constant different from that of the light-emitting layer 15 and distortion due to this lattice constant difference is applied to the light-emitting layer 15. Strain layer 14
When only the wavelength is added, the wavelength can be extended, but the output is about
Significantly reduced to 50 μW. This reduction in output is due to the light emitting layer 1
It is considered that No. 5 was affected by the thermal expansion of the substrate 10. On the other hand, by providing the strained layer 14 and the thermal expansion alleviating layer 12 as in this embodiment, the emission wavelength can be extended to about 520 nm, and a high output of about 200 μW can be obtained. This is presumably because the effect of the thermal expansion of the substrate 10 was removed by the thermal expansion moderating layer 12. By providing the strained layer 14 and the thermal expansion relaxation layer 12 in this manner, a longer wavelength and higher output can be realized.

In this embodiment, the composition of the thermal expansion relaxation layer 12 is In
_{Although 0.20} Ga _0.80 N has been set, it is sufficient that In _Y Ga _{1 -Y} N (0 ≦ Y ≦ 1) is satisfied. In particular, by adding In, the substrate 10 can be effectively reduced.
It is preferable that Y 望 ま し く 0 because the thermal stress can be reduced. The thickness of the thermal expansion moderating layer 12 may be 100 nm or more. If the film thickness of the thermal expansion relaxation coefficient 12 is less than 100 nm, the effect of relaxing the thermal stress is reduced, which is not desirable.
In the present embodiment, the composition of the strained layer 14 is Al _0.15 Ga _0.85 N, but it is sufficient that Al _X Ga _{1 -X} N (0 ≦ X ≦ 1) is satisfied.
In particular, by adding Al, it is possible to effectively impart distortion to the light emitting layer 15, so that X ≠ 0 is preferable. Also, strained layer 1
The film thickness of 4 may be in the range of 10 to 500 nm. Strain layer 14
If the film thickness is less than 10 nm, strain is not effectively applied to the light emitting layer 15, and if the film thickness is more than 500 nm, cracks occur, which is not desirable. In this embodiment, the light emitting element 10
0 has a MQW structure, but the SQW or In _0.2 G
a Single layer consisting of _0.8 N, etc., quaternary with any mixed crystal ratio,
Ternary AlInGaN may be used. MQW and SQW are more preferable because distortion is more likely to occur more effectively and the wavelength shift effect is increased. In addition, the present invention can be applied to light emitting elements such as LEDs and LDs and light receiving elements. In the present embodiment, the structure in which the strain layer 14 and the thermal expansion moderating layer 12 are provided is used. However, when the purpose is only to increase the wavelength, the output level is reduced, but only the strain layer 14 is provided. May be adopted.

As indicated above, according to the present invention,
By providing a semiconductor layer having a lattice constant different from that of the light-emitting layer on the substrate side of the light-emitting layer, strain is imparted to the light-emitting layer due to a difference in lattice constant between the light-emitting layer and the semiconductor layer, so that a longer wavelength can be obtained. Further, by providing the thermal expansion moderating layer, the influence of the thermal expansion of the substrate can be removed, so that high emission intensity can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a semiconductor light emitting device according to a specific example of the present invention.

FIG. 2 is a characteristic diagram showing the output and emission wavelength of a semiconductor light emitting device according to a specific example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Sapphire substrate 11 Buffer layer 12 Thermal expansion relaxation layer 13 High carrier concentration n ⁺ layer 14 Strain layer 15 Light emitting layer 16 Cladding layer 17 Contact layer 18A p electrode 18B n electrode 20 Electrode pad 100 Light emitting element 151 Barrier layer 152 Well layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinya Asami 1 Ochiai Nagahata, Kasuga-machi, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. Toyoda Gosei Co., Ltd.

Claims (2)

[Claims] A first semiconductor layer having a lattice constant different from that of the active layer is provided on the substrate side of the active layer, whereby the active layer is formed by a difference in lattice constant between the active layer and the first semiconductor layer. A strain is applied to the layer, and a second semiconductor layer for reducing the influence of the strain on the active layer due to thermal expansion of the substrate is provided on the substrate side with respect to the first semiconductor layer. A gallium nitride-based compound semiconductor device. 2. The method according to claim 1, wherein the first semiconductor layer is formed of Al _X Ga _{1 -X} N (0 <X ≦
1), wherein the second semiconductor layer is In _Y Ga _{1 -Y} N (0 <Y ≦ 1)
The gallium nitride-based compound semiconductor device according to claim 1, comprising: