JP3612985B2 - Gallium nitride compound semiconductor device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting device in which a layer made of a gallium nitride compound semiconductor is stacked on a substrate and a method for manufacturing the same, and more particularly to a light emitting device having a structure for increasing the light output and a method for manufacturing the same.
[0002]
[Prior art]
FIG. 3 shows a cross-sectional view of a light emitting device made of a gallium nitride compound semiconductor manufactured by a conventional technique. The element 100 is a double hetero blue LED, which is manufactured by a metal organic chemical vapor deposition method (hereinafter abbreviated as “MOVPE”).
As shown in FIG. 3, the device 100 includes a sapphire substrate 10, an AlN buffer layer 11, an n-type GaN cladding layer 12, a GaInN active layer 13, a p-type AlGaN cladding layer 14, a p-type GaN contact layer 15, and a positive electrode 16A. , A negative electrode 16B and an electrode pad 17.
[0003]
[Problems to be solved by the invention]
For example, in a conventional double hetero-type LED in which an active layer that emits light is made of GaInN, by reducing the In mole fraction of the GaInN active layer 13 in FIG. The light emission output of the element 100 was decreased. This is because, when manufacturing a double hetero type LED by MOVPE, undesired stress is easily generated in the GaInN active layer 13 in maintaining the light emission output, and In plays a role of relaxing the strain and suppressing this stress. It is thought that it is because it plays. That is, the device 100 can maintain the light emission output because the decrease of In that relaxes the strain makes it difficult to form localized electron levels that directly contribute to the light emission existing in the InGaN active layer 13. It seems impossible.
[0004]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a light-emitting element having a structure capable of maintaining a light emission output even when the light emission wavelength is made close to ultraviolet. .
[0005]
[Means for Solving the Problems]
In the light emitting device in which a layer made of a gallium nitride compound semiconductor is stacked on a substrate, the first means includes at least one layer from the substrate including the active layer that emits light to the active layer. And providing a strain relaxation layer having a thickness of 3000 to 6000 mm in which pits are formed to relieve strain on the crystal structure of the layer to be grown.
The second means is that the strain relaxation layer of the first means is constituted by a layer to which an impurity is added.
The third means is that the active layer is composed of a layer formed of Ga _x In _1-x N (0 ≦ x ≦ 1).
[0006]
In addition, as a method for producing a gallium nitride compound semiconductor device having the above structure, there are the following means.
That is, the fourth means lowers the stacking temperature from the first predetermined temperature to the second predetermined temperature as at least one layer from the substrate including the active layer that emits light to the active layer. In this method, a strain relaxation layer having a thickness of 3000 to 6000 mm in which pits are formed is laminated.
The fifth means is a method of forming the strain relaxation layer of the fourth means with n-type gallium nitride doped with silicon.
The sixth means is a method of setting the first predetermined temperature from 1000 ° C. to 1150 ° C.
The seventh means is a method of setting the second predetermined temperature from 500 ° C. to 950 ° C.
Further, the eighth means completes the formation of the active layer in any one of the fourth to seventh means before the pits of the strain relaxation layer are filled and flattened, whereby pits are also formed in the active layer. It is a method of forming.
Further, the ninth means is a method in which the active layer is formed by crystal growth of Ga _x In _1-x N (0 ≦ x ≦ 1) in any one of the fourth to eighth means.
The above-described problems can be solved by the above means.
[0007]
[Operation and effect of the invention]
In the case of hetero growth, the growth layer tends to be distorted. By providing a strain relaxation layer that relaxes the strain in the layer before reaching the active layer, the crystallinity of the active layer can be improved. As a result, the light output of the light emitting element can be improved.
For example, the conventional MOVPE double hetero-type LED element 100 shown in FIG. 3 has a mole fraction of In that plays a role in relaxing undesired crystal structural distortion in maintaining the light emission output in the GaInN active layer 13. It is considered that the emission output cannot be maintained because the localized level of electrons that directly contribute to the light emission existing in the GaInN active layer 13 is difficult to be formed.
Therefore, for example, as shown in FIG. 1, a layer having a pit having a thickness of 3000 to 6000 mm is provided below the active layer 23, and the active layer is laminated on the layer. As a result, the strain can be locally increased or decreased in the active layer, and the above-described strain is alleviated.
With the above operation, for example, even if the molar fraction of In in the GaInN active layer 23 in FIG. 1 is decreased, it is difficult to form localized levels of electrons that directly contribute to light emission, so that the light emission output can be maintained. it is conceivable that.
The above pits could be formed by crystal growth of the strain relaxation layer in a low temperature region of 500 ° C. to 950 ° C.
Further, the third means is to prevent the formation of a high electric field due to static electricity at the tip of the pit by adding an impurity to the strain relaxation layer to impart electrical conductivity. The dielectric breakdown in the strain relaxation layer is prevented, and the lifetime of the light emitting element can be maintained.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on specific examples.
FIG. 1 is a schematic cross-sectional configuration diagram of a light emitting device 200 formed of a GaN compound semiconductor formed on a sapphire substrate 20. A buffer layer 21 made of aluminum nitride (AlN) and having a thickness of about 200 mm is provided on the substrate 20, and a high carrier concentration n ^{+ having} a thickness of about 4.0 μm and made of silicon (Si) -doped GaN. A layer 22A is formed. On this high carrier concentration n ⁺ layer 22A, a clad layer 22B made of Si-doped n-type GaN and having a thickness of about 0.5 μm is formed.
Then, an active layer 23 having a thickness of about 500 mm is formed on the clad layer 22B and becomes the center of the single quantum well structure (SQW). On the active layer 23, a clad layer 24 made of p-type Al _0.15 Ga _0.85 N and having a thickness of about 600 mm is formed. Further, a contact layer 25 made of p-type GaN and having a thickness of about 1500 mm is formed on the cladding layer 24.
[0009]
Further, a translucent electrode 26A formed by metal deposition is formed on the contact layer 25, and an electrode 26B is formed on the n ⁺ layer 22A. The translucent electrode 26A is composed of cobalt (Co) having a thickness of about 15 mm bonded to the contact layer 25 and gold (Au) having a thickness of about 60 mm bonded to Co. The electrode 26B is made of vanadium (V) having a thickness of about 200 mm and aluminum (Al) or an Al alloy having a thickness of about 1.8 μm. On a part of the electrode 26A, an electrode pad 27 made of Co or Ni and Au, Al, or an alloy thereof and having a film thickness of about 1.5 μm is formed.
[0010]
Next, a method for manufacturing the light emitting element 200 will be described.
The light emitting device 200 was manufactured by vapor phase growth using MOVPE. The gases used were ammonia (NH ₃ ), carrier gas (H ₂ , N ₂ ), trimethyl gallium (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, the single crystal substrate 20 having the a-plane cleaned by organic cleaning and heat treatment is mounted on a susceptor mounted in a reaction chamber of the MOVPE apparatus. Next, the substrate 20 was baked at a temperature of 1150 ° C. while flowing H ₂ into the reaction chamber at normal pressure.
Next, the temperature of the substrate 20 was lowered to 400 ° C., and H ₂ , NH ₃ and TMA were supplied to form the AlN buffer layer 21 with a film thickness of about 200 mm.
[0011]
Next, the temperature of the substrate 20 is increased to 1150 ° C., and H ₂ , NH ₃ , TMG and silane are supplied, and the silicon (Si) doping is performed with a film thickness of about 4.0 μm and an electron concentration of 2 × 10 ¹⁸ / cm ^3. A high carrier concentration n ⁺ layer 22A made of GaN was formed.
Next, a strain relaxation layer having pits was formed. That is, the temperature of the substrate 20 is lowered to 900 ° C., N ₂ or H ₂ , NH ₃ , TMG and silane are supplied, and silicon having a film thickness of about 0.5 μm and an electron concentration of 1 × 10 ¹⁸ / cm ³ ( A cladding layer 22B having a large number of pits made of Si) -doped GaN was formed. This clad layer 22B becomes a strain relaxation layer.
After forming the clad layer 22B, the crystal temperature is lowered to 850 ° C., and N ₂ or H ₂ , NH ₃ , TMG and TMI are supplied to form a Ga _0.8 In _0.2 N film having a thickness of about 500 mm. An active layer 23 made of The active layer 23 was laminated before the pits of the cladding layer 22B were filled and flattened. As a result, as shown in FIG. 1, pits could be formed on the active layer 23 itself.
[0012]
Next, the temperature of the substrate 20 is raised to 1000 ° C., N ₂ or H ₂ , NH ₃ , TMG, TMA and CP ₂ Mg are supplied, and the p-type doped with magnesium (Mg) is about 50 nm thick. A clad layer 24 made of Al _0.15 Ga _0.85 N was formed.
Next, the temperature of the substrate 20 is kept at 1000 ° C., and N ₂ or H ₂ , NH ₃ , TMG and CP ₂ Mg are supplied, and the contact layer 25 made of p-type GaN doped with Mg and having a thickness of about 100 nm. Formed.
Next, an etching mask is formed on the contact layer 25, the mask in a predetermined region is removed, and the portions of the contact layer 25, the cladding layer 24, the active layer 23, the cladding layer 22B, and the n ⁺ that are not covered with the mask. A part of the layer 22A was etched by reactive ion etching using a gas containing chlorine to expose the surface of the n ⁺ layer 22A.
Next, an electrode 26B for the n ⁺ layer 22A and a translucent electrode 26A for the contact layer 25 were formed by the following procedure.
[0013]
(1) A photoresist is applied, a window is formed in a predetermined region on the exposed surface of the n ⁺ layer 22A by photolithography, and after evacuating to a high vacuum of the order of 10 ⁻⁶ Torr or less, vanadium having a film thickness of about 200 mm (V) and Al having a film thickness of about 1.8 μm were deposited. Next, the photoresist is removed. As a result, an electrode 26B is formed on the exposed surface of the n ⁺ layer 22A.
(2) Next, a photoresist is uniformly applied on the surface, and the photoresist in the electrode formation portion on the contact layer 25 is removed by photolithography to form a window portion.
(3) After evacuating to a high vacuum of the order of 10 ⁻⁶ Torr or less on the photoresist and the exposed contact layer 25 with a vapor deposition apparatus, a Co film having a thickness of about 15 mm is formed, and a film is formed on the Co. An Au film having a thickness of about 60 mm is formed.
[0014]
(4) Next, the sample is taken out from the vapor deposition apparatus, Co and Au deposited on the photoresist are removed by a lift-off method, and a translucent electrode 26A is formed on the contact layer 25.
(5) Next, in order to form a bonding electrode pad 27 on a part of the translucent electrode 26A, a photoresist is uniformly applied and applied to the photoresist in the portion where the electrode pad 27 is formed. Open the window. Next, Co or Ni and Au, Al, or an alloy thereof is deposited to a thickness of about 1.5 μm by vapor deposition, and deposited on the photoresist by the lift-off method in the same manner as the step (4). The electrode pad 27 is formed by removing the film made of Co or Ni and Au, Al, or an alloy thereof.
(6) Thereafter, the sample atmosphere is evacuated with a vacuum pump, O ₂ gas is supplied to a pressure of 3 Pa, and in this state, the atmosphere temperature is set to about 550 ° C., and heating is performed for about 3 minutes. 24 was reduced in p-type resistance, alloyed with the contact layer 25 and the electrode 26A, and alloyed with the n ⁺ layer 22A and the electrode 26B. In this way, the light emitting element 200 was formed.
[0015]
FIG. 2 is a measurement diagram showing the wavelength characteristics of the photoluminescence intensity of the active layer of the gallium nitride compound semiconductor device. Graph A is a measurement diagram showing the wavelength characteristics of the photoluminescence intensity of the active layer of the light emitting device 200 according to the present invention. The thickness of the n-type GaN cladding layer 22B in which pits are formed is 6000 mm, and the growth temperature is 900. The thing of ° C was measured. Graph B is a measurement diagram showing the wavelength characteristics of the photoluminescence intensity of the active layer of the light emitting device according to the prior art.
From this figure, it can be seen that the emission intensity of the gallium nitride-based compound semiconductor device according to the present invention is remarkably increased as compared with the conventional one.
[0016]
Although the active layer 23 of the light emitting device 200 has an SQW structure, the structure of the active layer may be an MQW structure. The active layer, the clad layer, the contact layer, and the other layers are formed of any mixed crystal ratio of quaternary, ternary, and binary Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ It is good also as y <= 1). Further, Mg is used as the p-type impurity, but a Group 2 element such as beryllium (Be) or zinc (Zn) can be used.
In general, in order to form a strain relaxation layer having pits, the layer may be grown at a temperature lower than the normal crystal growth temperature of the layer. In the case of a gallium nitride compound semiconductor device, the low temperature region is 500 From 950 ° C to 950 ° C.
In the above embodiment, the cladding layer is a strain relaxation layer, but normal growth is performed after Ga _0.8 In _0.2 N is grown at a low temperature and pits are formed in the initial stage of growing the active layer 23. A method of forming the active layer by raising the temperature is also conceivable.
Further, a compound represented by the general formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is grown at a low temperature below the cladding layer to form pits. And it is good also as a distortion relaxation layer.
The thickness of the pit layer is about 3000 to 6000 mm, which is the most appropriate range. If the thickness is smaller than this, the distortion of the active layer is difficult to be relaxed, and if it is thicker than this, the crystallinity of the active layer is deteriorated. Tend to.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a gallium nitride compound semiconductor device according to the present invention.
FIG. 2 is a measurement diagram showing wavelength characteristics of photoluminescence intensity of an active layer of a gallium nitride-based compound semiconductor device.
FIG. 3 is a cross-sectional view of a conventional gallium nitride compound semiconductor device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100,200 ... Double hetero type | mold LED light emitting element 10,20 ... Sapphire substrate 11,21 ... AlN buffer layer 12,22A ... n-type GaN clad layer 22B ... n-type GaN clad layer 13 with pit formed ... GaInN active layer 23 ... GaInN active layers 14, 24 with pits formed ... p-type AlGaN cladding layers 15, 25 ... p-type GaN contact layers 16A, 26A ... positive electrodes 16B, 26B ... negative electrodes 17, 27 ... electrode pads

Claims (9)

In a light emitting device in which a layer made of a gallium nitride compound semiconductor is stacked on a substrate,
At least one layer from the substrate including the active layer that emits light to the active layer is formed with pits for relaxing distortion on the crystal structure of the layer grown on the substrate, and has a thickness of 3000 mm. A gallium nitride-based compound semiconductor device characterized in that a strain relaxation layer of 1 to 6000 mm is provided. The gallium nitride-based compound semiconductor device according to claim 1, wherein an impurity is added to the strain relaxation layer. The gallium nitride-based compound semiconductor device according to claim 1, wherein the active layer is Ga _x In _1-x N (0 ≦ x ≦ 1). A method of manufacturing a light emitting device in which a layer made of a gallium nitride compound semiconductor is stacked on a substrate,
Pits were formed by lowering the growth temperature from a first predetermined temperature to a second predetermined temperature as at least one layer from the substrate including the active layer that emits light to the active layer. A method of manufacturing a gallium nitride-based compound semiconductor device comprising laminating a strain relaxation layer having a thickness of 3000 to 6000 mm . 5. The method of manufacturing a gallium nitride compound semiconductor device according to claim 4, wherein the strain relaxation layer is formed of n-type gallium nitride doped with silicon. 6. The method for manufacturing a gallium nitride-based compound semiconductor device according to claim 4, wherein the first predetermined temperature is 1000 ° C. to 1150 ° C. The method of manufacturing a gallium nitride compound semiconductor device according to any one of claims 4 to 6, wherein the second predetermined temperature is 500 ° C to 950 ° C. The pits are also formed in the active layer by completing the stacking of the active layer before the pits of the strain relaxation layer stacked before the active layer are filled and flattened. The method for manufacturing a gallium nitride-based compound semiconductor device according to any one of claims 4 to 7. The gallium nitride system according to claim 4, wherein the active layer is formed by crystal growth of Ga _x In _1-x N (0 ≦ x ≦ 1). A method for manufacturing a compound semiconductor device.

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