JP4948720B2 - Nitrogen compound semiconductor laminate, light emitting element, optical pickup system, and method for producing nitrogen compound semiconductor laminate. - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laminate made of a nitrogen compound semiconductor, a light emitting device using the laminate, an optical pickup system using the light emitting device, and a method for manufacturing the laminate.
[0002]
[Prior art]
Research and development of light emitting devices and high power devices are advancing using the characteristics of nitrogen compound semiconductors. For example, in the case of a light-emitting element, a wide light-emitting element from violet to orange can be technically obtained by adjusting the composition of the nitrogen compound semiconductor to be used. In recent years, blue light emitting diodes and green light emitting diodes have been put to practical use by utilizing the characteristics of nitrogen compound semiconductors, and blue-violet semiconductor lasers have been developed as semiconductor laser elements.
[0003]
When manufacturing a nitrogen compound semiconductor film, a substrate such as sapphire, SiC, spinel, Si, GaAs, or GaN is used as a substrate. For example, when sapphire is used as a substrate, before the GaN film is epitaxially grown, a buffer layer of GaN or AlN is previously formed on the substrate at a low temperature of 500 ° C. to 600 ° C., and then the substrate is formed at 1000 ° C. to 1100. It is known that when a nitrogen compound semiconductor film is epitaxially grown by raising the temperature to a high temperature of 0 ° C., a crystal having a good surface state and a good structural and electrical property can be obtained. When using SiC as a substrate, it is known that a thin AlN film should be used as a buffer layer at a temperature at which epitaxial growth is performed.
[0004]
However, when a substrate other than a nitrogen compound semiconductor is used, a large number of defects exist in the manufactured nitrogen compound semiconductor due to a difference in thermal expansion coefficient and a lattice constant between the growing nitrogen compound semiconductor film and the substrate. The defect density is about 2 × 10 in total.⁷cm^-2~ 1x10⁹cm^-2It also becomes. Many such dislocations are known to trap carriers that control electrical conduction in semiconductor films, for example, and impair the electrical characteristics of the manufactured films. It is known that the lifetime of the element is reduced. Therefore, in order to reduce lattice defects and improve electrical characteristics, nitrogen compound semiconductors such as GaN are used using techniques such as hydride vapor phase epitaxy (H-VPE), high-pressure synthesis, and sublimation. An attempt has been made to form a thick film and use the thick film as a substrate.
[0005]
[Problems to be solved by the invention]
However, when a new nitrogen compound semiconductor crystal is grown on a substrate obtained from a thick film of a nitrogen compound semiconductor (hereinafter referred to as a nitrogen compound semiconductor substrate), the flatness of the crystal surface is compared with the original substrate surface. May get worse. This is due to the surface state of the nitrogen compound semiconductor substrate. It is known that the surface of a thick nitrogen compound semiconductor film can have a slight deviation in the c-axis direction and the a-axis direction. Therefore, when a crystal of a nitrogen compound semiconductor is grown on a nitrogen compound semiconductor substrate, a stable surface of crystal growth is formed in a slightly different direction in many regions, which impairs the flatness of the growth film. It can be a cause. A light-emitting element with poor surface flatness can generate a significant distribution of emission intensity in the plane. Such a distribution may cause a phenomenon that the threshold current for starting oscillation is increased in the laser element, or that the far-field image or the near-field image is not stable in the optical pickup system using the laser element.
[0006]
One object of the present invention is to provide a stack of nitrogen compound semiconductors having a flat surface.
[0007]
A further object of the present invention is to provide a nitrogen compound semiconductor laminate useful for light emitting devices such as semiconductor lasers and light emitting diodes.
[0008]
A further object of the present invention is to provide a light emitting device with improved characteristics.
It is a further object of the present invention to provide an optical pickup system with improved performance.
[0009]
It is a further object of the present invention to provide a method for forming a flat crystalline layer on a nitrogen compound semiconductor crystal.
[0010]
[Means for Solving the Problems]
In order to solve the above problem, when a nitrogen compound semiconductor is epitaxially grown on a substrate, it is necessary to integrate stable crystal planes individually generated from minute regions in the substrate in the same direction. In response to this problem, the present inventors can obtain a crystal layer having a very flat surface by growing a crystal layer of a nitrogen compound semiconductor on a substrate through a nitrogen compound semiconductor layer doped with carbon. As a result, the present invention has been completed.
[0011]
According to the present invention, there is provided a nitrogen compound semiconductor laminate, and the laminate comprises a first crystal layer made of a nitrogen compound semiconductor, a nitrogen compound semiconductor formed directly on the first crystal layer and containing carbon as an impurity. An intermediate layer and a second crystal layer formed directly on the intermediate layer and made of a nitrogen compound semiconductor are provided.
[0012]
In the laminate according to the present invention, the thickness of the intermediate layer is preferably 5 nm to 500 nm, more preferably 10 nm to 200 nm. The concentration of carbon in the intermediate layer is 5 × 10.¹⁸cm^-35 × 10 or more^{twenty one}cm^-3The following is preferable.
[0013]
In the present invention, the first crystal layer can contain gallium and nitrogen as main components. In this case, the nitrogen compound semiconductor of the intermediate layer is GaN and Al._xGa_1-xIt is preferable to be selected from the group consisting of N (0 ≦ x ≦ 1). In the case of AlGaN, the intermediate layer nitrogen compound semiconductor is Al._xGa_1-xN (0 ≦ x ≦ 0.3) is more preferable. Carbon can be efficiently added to these nitrogen compound semiconductors.
[0014]
In the stack according to the invention, typically the second crystalline layer is an epitaxially grown layer. You may provide the laminated body of this invention as an epitaxial wafer for forming an element on it. In the laminate or the epitaxial wafer, the surface roughness Ra of the second crystal layer is typically 30 nm or less.
[0015]
In addition, a light-emitting element is provided by the present invention, and the light-emitting element is formed on the above-described nitrogen compound semiconductor laminate, the second crystal layer of the laminate, and includes a nitrogen compound semiconductor. A laminated structure for generating the electrode and an electrode for supplying electric power to the laminated structure are provided. The light emitting element is, for example, a semiconductor laser.
[0016]
Furthermore, an optical pickup system according to the present invention is provided, which system comprises a light emitting device according to the present invention, in particular a semiconductor laser, as a device for supplying light to the optical system.
[0017]
Moreover, the manufacturing method of a nitrogen compound semiconductor laminated body is provided by this invention. The manufacturing method includes a nitrogen compound semiconductor containing carbon as an impurity from a carbon source, a group 3 element source in the periodic table, and a nitrogen source on a first crystal layer made of a nitrogen compound semiconductor. And the supply of the carbon source is stopped, and the nitrogen compound semiconductor is supplied from the group 3 element source and the nitrogen source in the periodic table in succession to the first step. A second step of forming a second crystal layer comprising: In this manufacturing method, the first step and the second step are preferably performed by metal organic vapor phase epitaxy.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Typically, the laminate according to the present invention has a structure as shown in FIG. In the nitrogen compound semiconductor laminate 10, a nitrogen compound semiconductor intermediate layer 12 containing carbon as an impurity is formed on a first crystal layer 11 made of a nitrogen compound semiconductor, and a nitrogen compound semiconductor intermediate layer 12 is formed thereon. Two crystal layers 13 are formed. The intermediate layer 12 is in contact with both the first and second crystal layers. In general, the intermediate layer 12 is thinner than the second crystal layer 13. As will be described below, the intermediate layer 12 contributes to smoothing the surface of the second crystal layer 13. Typically, the first crystal layer is a single crystal layer, and the second crystal layer is an epitaxial growth layer.
[0019]
In the laminate according to the present invention, the first crystal layer may be a nitrogen compound semiconductor substrate, or may be formed on another substrate such as sapphire. When the first crystal layer forms a substrate, the thickness thereof is, for example, 20 to 2000 μm, preferably 100 to 500 μm. On the other hand, when the first crystal layer is formed on another substrate such as sapphire, the thickness is, for example, 3 to 500 μm, and preferably 10 to 200 μm. The first crystal layer can be formed of gallium nitride (GaN), indium nitride (InN), aluminum nitride (AlN), InGaN, AlGaN, InGaN, or the like. Typically, the first crystal layer is mainly composed of gallium and nitrogen. In particular, GaN is preferable for the first crystal layer. A preferable material for the first crystal layer is a nitrogen compound semiconductor in which a part of Ga in GaN is substituted with Al, In, or both, such as AlGaN, InGaN, and InGaAlN. The first crystal layer may contain an impurity of an appropriate conductivity type (typically n-type) at an appropriate density.
[0020]
In the laminate according to the present invention, the intermediate layer made of a nitrogen compound semiconductor doped with carbon plays a role of flattening the surface of the second crystal layer formed thereon. If the second crystal layer is provided on the first crystal layer via the intermediate layer, the stable crystal planes generated in the minute regions can be integrated, and the surface of the second crystal layer can be made flat. can do. As will be described later, the extremely flat surface caused by the intermediate layer can reduce unevenness of light emission in the light emitting element, and can provide uniform light emission characteristics and strong light emission intensity.
[0021]
Nitrogen compound semiconductors that form the intermediate layer include GaN and Al_xGa_1-xN (0 <x <1), In_yGa_1-yN (0 <y <1), AlN, InN, In_xGa_yAl_{1- (x + y)}N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). GaN and Al_xGa_1-xN (0 ≦ x ≦ 0.3) is more preferable as a material for the intermediate layer. As will be described later, a laminate or an element structure having a very flat surface can be obtained by using a nitrogen compound semiconductor having an appropriate composition for the intermediate layer. The flat surface improves the in-plane uniformity of the emission intensity and increases the emission intensity in the light emitting element.
[0022]
FIG. 2 shows the result of analyzing a nitrogen compound semiconductor laminate for a light-emitting element by secondary ion mass spectrometry (SIMS). In FIG. 2, the peak represents a portion of the intermediate layer containing carbon as an impurity. Accordingly, the right side of the peak represents the first crystal layer (for example, GaN substrate), and the left side of the peak represents the second crystal layer (for example, the nitrogen compound semiconductor layer for the light emitting element). . Typically, the laminate according to the present invention has a structure in which an intermediate layer having a significantly higher carbon concentration than those layers is sandwiched between the first crystal layer and the second crystal layer, as shown in FIG. Have Typically, the carbon concentration distribution in the intermediate layer is as shown in FIG. 2, where the carbon concentration is highest at any position of the intermediate layer (eg, the middle position of the intermediate layer) It decreases as it goes from the point to the first and second crystal layers. In the present invention, the intermediate layer can be said to be a layer having a significantly higher carbon concentration than the first and second crystal layers, but the thickness is specified as a clear value due to the distribution of the carbon concentration. It may be difficult. Therefore, in this specification, the value obtained as follows is defined as the thickness of the intermediate layer. First, the carbon concentration distribution with respect to the depth as shown in FIG. 2 is obtained by SIMS analysis. Next, paying attention to the peak of the carbon concentration in the obtained chart, as shown in FIG. 3, the peak width (half width) w of the portion corresponding to 1/2 of the maximum value of the peak is defined as the thickness of the intermediate layer. (However, FIG. 3 shows an example in which the vertical axis is a linear scale, and even when it is not a linear scale, the thickness can be defined from the width of a portion corresponding to a half value according to this) . The maximum value of the peak is the height of the vertex with respect to the background.
[0023]
In the present invention, the thickness of the intermediate layer is set so that the crystallinity of the second crystal layer can be kept good. The thickness of the intermediate layer is generally 5 nm to 500 nm, preferably 10 nm to 200 nm. By using an intermediate layer having a thickness within these ranges, it is possible to effectively reduce the influence of independent formation of crystal planes in a minute region, and to effectively bring a smooth surface to the second crystal layer. Can do. Moreover, if the second crystal layer is formed on the intermediate layer having a thickness within these ranges, good crystallinity and electrical characteristics can be obtained. On the other hand, when the intermediate layer becomes extremely thin, the effect of providing a smooth surface due to the integration of crystal planes becomes small. When the intermediate layer is extremely thick, the crystallinity of the second crystal layer may be deteriorated.
[0024]
The concentration of carbon contained in the intermediate layer is 5 × 10¹⁸cm^-3~ 5x10^{twenty one}cm^-3Is preferred. This concentration range can effectively reduce the influence of the independent formation of crystal planes, particularly in a minute region, and can effectively bring a smooth surface to the second crystal layer.
[0025]
In the present invention, the second crystal layer can be formed of gallium nitride (GaN), indium nitride (InN), aluminum nitride (AlN), InGaN, AlGaN, InGaAlN, or the like. Typically, the second crystal layer is mainly composed of gallium and nitrogen. In particular, GaN is preferable for the second crystal layer. A preferable material for the second crystal layer is a nitrogen compound semiconductor in which a part of Ga in GaN is substituted with Al, In, or both, such as AlGaN, InGaN, and InGaAlN. The second crystal layer may contain an impurity of an appropriate conductivity type (typically n-type) at an appropriate density. The thickness of the second crystal layer is, for example, 0.1 to 10 μm, and preferably 1 to 5 μm.
[0026]
The nitrogen compound semiconductor laminate according to the present invention can be provided as a wafer useful for the production of devices. In this case, the second crystal layer is typically an epitaxial growth layer. Regarding the surface of the wafer (the surface of the second crystal layer), the surface roughness Ra is typically less than 30 nm, preferably 20 nm or less. The range of the surface roughness Ra is typically 1 to 20 nm, preferably 1 to 10 nm. Here, the surface roughness is the centerline average roughness, and the measurement length is 100 μm to 1 mm, typically 300 μm. Ra described in the present example was measured by scanning 300 μm using Dektak 3ST manufactured by Sloan.
[0027]
The nitrogen compound semiconductor laminate according to the present invention can be used for various elements including light emitting elements such as light emitting diodes and semiconductor lasers, power devices and the like. In these elements, the nitrogen compound semiconductor laminate according to the present invention typically constitutes a substrate portion. The nitrogen compound semiconductor laminate according to the present invention can drastically improve the flatness of the element surface, and as a result, the performance of the element can be improved.
[0028]
In particular, the light emitting device according to the present invention can have a light emitting surface with significantly improved flatness. In such a light emitting element, in-plane light emission distribution (light emission unevenness) is small, and uniform light emission characteristics can be obtained. In such a light-emitting element, loss in light propagation can be reduced and the threshold current density can be lowered. In particular, in a quantum well type light emitting device, such an improvement in characteristics can be remarkable, and a stable and strong light emission intensity can be obtained. A light emitting element includes any element that provides light output. Typical light-emitting elements include light-emitting diodes and semiconductor lasers. Typically, the present invention applies to double heterojunction lasers, particularly quantum well lasers.
[0029]
Specifically, a light emitting device according to the present invention includes the above-described nitrogen compound semiconductor laminate, a laminate structure formed on the second crystal layer and made of a nitrogen compound semiconductor for generating light output from power, And an electrode for supplying electric power to the laminated structure. The laminated structure for optical output includes an n-type cladding layer, an active layer, and a p-type cladding layer in a double heterojunction structure. The active layer is preferably a quantum well layer. The electrode includes a p-electrode and an n-electrode. When the nitrogen compound semiconductor laminate according to the present invention is used as a substrate, an electrode (typically an n-electrode) can be formed on the surface of the first crystal.
[0030]
The light emitting device according to the present invention, particularly the semiconductor laser, is useful for an optical pickup system. Specifically, the present invention provides an optical pickup system having the light emitting element as a device for supplying light to an optical system. The optical system includes appropriate elements depending on the application. For example, the optical system includes a collimator lens that receives light from a semiconductor laser, a diffraction grating, a polarizing beam splitter, a quarter-wave plate, an objective lens, and a photodetector. A normal optical system can be used. In an optical pickup system, a semiconductor laser (for example, a semiconductor laser having a cleavage plane) according to the present invention can form a far-field image and a near-field image with stable characteristics, and improve the reading and writing accuracy of the system. Can do.
[0031]
The nitrogen compound semiconductor laminate according to the present invention is particularly effective when the thickness of the first crystal layer exceeds 100 μm. In the nitrogen compound semiconductor substrate (first crystal layer) having a thickness exceeding 100 μm, there can be many micro cracks or concentrated dislocations generated during manufacturing. As a result of experiments of the present invention, it was found that the intermediate layer containing carbon can significantly reduce the influence of microcracks and dislocations on the second crystal layer.
[0032]
Moreover, the nitrogen compound semiconductor laminate according to the present invention is particularly effective for the first crystal layer formed by the vapor phase growth method. On the surface of a thick nitrogen compound semiconductor formed by a vapor phase growth method such as H-VPE method or MOCVD method, irregularities having a surface roughness Ra exceeding 50 nm may exist. This unevenness is caused by the aggregation of nitrogen compound semiconductor molecules in the gas phase in the process of obtaining a thick film. When a crystal layer of a nitrogen compound semiconductor is formed directly on a surface having unevenness, the unevenness may be reflected as it is on the surface of the obtained crystal layer, or the unevenness may be amplified. As a result of experiments by the present inventors, it has been found that the intermediate layer containing carbon significantly reduces the influence of such unevenness.
[0033]
The nitrogen compound semiconductor laminate according to the present invention can be prepared by the following process. First, a nitrogen compound semiconductor containing carbon as an impurity is formed from a carbon supply source, a group 3 element supply source in the periodic table, and a nitrogen supply source on a first crystal layer made of a nitrogen compound semiconductor. . The first crystal layer may be a nitrogen compound semiconductor substrate manufactured by a vapor deposition method or the like, or may be formed on another substrate such as sapphire. The carbon source and the Group 3 element source can each be a compound capable of releasing the corresponding element by pyrolysis, such as an organic compound, halide, or hydride. The source of nitrogen is a compound capable of supplying N by thermal decomposition, preferably ammonia (NH_Three). By this step, a carbon-doped nitrogen compound semiconductor layer is formed on the first crystal layer. The doping concentration of carbon can be adjusted by supplying the carbon source and the temperature. Subsequently, continuously with this step, the supply of the carbon source is stopped, and a second crystal layer made of a nitrogen compound semiconductor is formed from the Group 3 element supply source and the nitrogen supply source. The source of the Group 3 element and / or the source of nitrogen is preferably the same as in the formation of the carbon doped layer, but may be different. Moreover, you may add the supply source of a different group 3 element. Typical Group 3 elements used are Ga, Al and In. These steps are preferably performed by metal organic vapor phase epitaxy.
[0034]
Hereinafter, the present invention will be described in more detail based on specific examples. In a specific example of the present invention, the nitrogen compound semiconductor substrate can be manufactured by a hydride vapor phase epitaxy method (H-VPE method), a high-pressure synthesis method, a sublimation method, or the like. Examples of the material of the nitrogen compound semiconductor substrate include gallium nitride (GaN), indium nitride (InN), aluminum nitride (AlN), InGaN, AlGaN, InGaAlN, and the like. Typically, gallium nitride (GaN) is used. Impurities doped in the nitrogen compound semiconductor substrate include silicon (Si), chlorine (C1), magnesium (Mg), oxygen (0), and the like. Doped nitrogen compound semiconductor substrates are often used to fabricate devices. The surface of the substrate may remain as obtained by the above-described manufacturing method, or may be physically or chemically polished. When the thickness of the nitrogen compound semiconductor exceeds 100 μm, the substrate can be constituted by only the semiconductor. On the other hand, when the thickness of the nitrogen compound semiconductor is 100 μm or less, a substrate in which a crystal layer of the nitrogen compound semiconductor is formed on a base made of sapphire or the like can be preferably used.
[0035]
Example 1
In summary, this example performed the following steps. A GaN thick film doped with Si with a thickness of 500 μm was formed on a sapphire substrate using the H-VPE method. The GaN thick film was removed from the sapphire substrate and used as a nitrogen compound semiconductor substrate. A GaN film containing carbon as an impurity and a GaN film having a thickness of about 4 μm were formed on the substrate by metal organic chemical vapor deposition (MOCVD), respectively. The detailed process is described below.
[0036]
First, the cleaned 2-inch sapphire substrate was introduced into an H-VPE apparatus and heated at 1000 ° C. Hydrogen chloride (HCl) 300 CC / min passed through gallium (Ga) heated to 800 ° C. and nitrogen gas (N₂) After flowing 1000 CC / min for about 15 minutes, ammonia (NH 3) was added at 1000 CC / min, dichlorosilane (SiH₂Cl₂) Was introduced at a flow rate of 100 nmol / min, and GaN was grown on the substrate for about 2 hours. Next, the supply of hydrogen chloride and dichlorosilane was stopped, and the temperature of the substrate was lowered. When the temperature reached room temperature, the supply of ammonia was stopped, and the grown GaN film was taken out of the H-VPE apparatus together with the sapphire substrate. Most of the GaN film on sapphire grown in this way peeled naturally when the temperature fell due to the difference in thermal expansion between sapphire and GaN. The naturally exfoliated GaN film had a thickness of about 400 to 500 μm. The back surface of the GaN thick film obtained as described above (the side that was in contact with the sapphire substrate; hereinafter referred to as the back surface of the GaN substrate) was severely uneven, and was polished flat using diamond powder. Moreover, although the surface of the GaN thick film (the surface facing the back surface, hereinafter referred to as the GaN substrate surface) generated sparse micro hexagonal irregularities, most of the surface was a mirror surface visually ( Hereinafter, the obtained substrate is referred to as a GaN substrate).
[0037]
Next, after cleaning the GaN substrate with acetone and ethanol, the GaN substrate is introduced into the MOCVD apparatus, and has a GaN film containing carbon and a thickness of about 4 μm on the surface of the GaN substrate in the following procedure. GaN films were grown sequentially. Hereinafter, description will be given with reference to FIG. First, the temperature was raised to 800 ° C. over about 15 minutes while flowing 5000 cc / min of nitrogen and 1000 cc / min of hydrogen through the GaN substrate 201 set in the MOCVD apparatus. At that time, ammonia was introduced at a flow rate of 4000 cc / min when the temperature exceeded 400 ° C. so that GaN was not decomposed by heat. When the temperature reaches 800 ° C., trimethylgallium (TMG) as a raw material for Group 3 elements is 20 μmol / min, and carbon tetrabromide (CBr as carbon material)._Four) Was introduced at a flow rate of 20 μmol / min, and a carbon-doped GaN film 202 was grown to a thickness of about 20 nm. Thereafter, the supply of carbon tetrabromide was stopped, the temperature of the substrate was raised to 1050 ° C., the supply amount of trimethylgallium was increased to 100 μmol / min, and the growth of the GaN film 203 was started. In this way, a GaN film 204 having a thickness of about 4 μm was grown over 1 hour. When the growth was completed, the supply of trimethylgallium was stopped and the temperature of the substrate was lowered. When the temperature of the substrate reached room temperature, supply of ammonia and nitrogen was stopped, and the obtained GaN substrate having the GaN epitaxial growth film was taken out from the apparatus.
[0038]
About the obtained nitrogen compound semiconductor laminated body, as a result of measuring the carbon concentration in the carbon-doped GaN film 202 using a secondary ion mass spectrometry (SIMS) apparatus, a chart as shown in FIG. 2 was obtained. The carbon concentration in the layer is about 1 × 10²⁰cm^-3Met. In the above process, the reason why the growth temperature of the GaN film doped with carbon is lower than the growth temperature of the GaN film not doped with carbon is that carbon is efficiently doped. In the case of doping carbon by increasing the growth temperature, it was necessary to increase the amount of carbon tetrabromide introduced. On the other hand, if the carbon was doped at a lower growth temperature, the amount of carbon tetrabromide introduced could be reduced. The surface roughness Ra of the surface of the obtained GaN film 204 was about 5 nm.
[0039]
Example 2
A carbon doped layer and a GaN epitaxial growth layer were formed on the GaN substrate obtained in Example 1, and a light emitting diode (LED) as shown in FIG. 5 was produced thereon. Hereinafter, the manufacturing process will be described with reference to FIG.
[0040]
First, in order to give n-type conductivity to the GaN substrate, Si was doped into the substrate as an impurity according to a conventional method. Thereby, an electrode can be formed in the lower part of the substrate, which is effective for extracting light. A conductive Si-doped GaN substrate 102 is set in an MOVCD apparatus, and in the same manner as the GaN film described above, a temperature of 800 ° C. is applied over about 15 minutes while flowing 5000 cc / min of nitrogen and 1000 cc / min of hydrogen. The temperature was raised to. At that time, ammonia was introduced at a flow rate of 4000 cc / min when the temperature exceeded 400 ° C. so that GaN was not decomposed by heat. When the temperature reaches 800 ° C., trimethylgallium (TMG) as a raw material for Group 3 elements is 20 μmol / min, and carbon tetrabromide (CBr as carbon material)._Four) Was introduced at a flow rate of 20 μmol / min, and a carbon-doped GaN film 103 was grown to a thickness of about 20 nm. Thereafter, the supply of carbon tetrabromide is stopped, the temperature of the substrate is raised to 1050 ° C., the supply amount of trimethylgallium is increased to 100 μmol / min, and monosilane (SiH_Four) Was supplied at 5 nmol / min, and the growth of the GaN film 901 was started. In this way, after the growth of the GaN film 901 having a thickness of about 4 μm over 1 hour, the supply of trimethylgallium and monosilane was stopped, and the temperature of the substrate was lowered to about 750 ° C. When the substrate temperature reaches 750 ° C., trimethylgallium and In raw materials are supplied, and three pairs of In_0.05Ga_0.95N / In_0.35Ga_0.65A light emitting layer 902 made of N was formed. Thereafter, the supply of the trimethylgallium and In raw materials was stopped, the growth temperature was raised again to 1050 ° C., and a 30 nm thick Al was sequentially formed._0.2Ga_0.8Carrier block layer 903 made of N, 1 × 10 5 Mg as a p-type carrier dopant¹⁸cm^-3A p-type GaN contact layer 904 having a thickness of 0.3 μm was formed. Bisethylcyclopentadienylmagnesium (EtCp2Mg) was used as a material for doping Mg. Further, trimethylindium was used as the In raw material, and trimethylaluminum was used as the A1 raw material. Next, the supply of the Group 3 element material was stopped, the substrate temperature was lowered to room temperature, and the preparation of the LED layer structure was completed. Regarding the outermost surface of the obtained LED structure, the surface roughness Ra was 5 nm. Next, necessary electrodes were formed to obtain a light emitting diode. In the obtained light emitting diode, the emission center wavelength was 460 nm. When the light emitting surface was observed with a microscope, the light was emitted uniformly within the surface, and no unevenness in intensity and color was observed.
[0041]
Comparative Example 1
In this comparative example, a GaN film having a thickness of 4 μm was formed directly on a GaN substrate manufactured by the same method as in Example 1 without forming a carbon-doped GaN film, and then a nitrogen compound was formed thereon. A semiconductor light emitting device was formed. Hereinafter, the process will be described with reference to FIG. Similar to Example 1, the GaN substrate 201 set in the MOCVD apparatus was heated to a temperature of 1050 ° C. over about 15 minutes while flowing 5000 cc / min of nitrogen and 1000 cc / min of hydrogen. At that time, ammonia was introduced at a flow rate of 4000 cc / min when the temperature exceeded 400 ° C. so that GaN was not decomposed by heat. When the temperature reached 1050 ° C., trimethylgallium (TMG) was introduced as a Group 3 element material at a flow rate of 100 μmol / min, and growth of the undoped GaN film 212 was started. The undoped GaN film had many hexagonal pyramidal protrusions from the beginning of growth, and the unevenness due to the protrusions tended to increase little by little as the growth time passed (213). The unevenness did not increase further when the value became constant. In this way, a GaN film 214 having a thickness of about 4 μm was formed over 1 hour. When the growth was completed, the supply of trimethylgallium was stopped and the temperature of the substrate was lowered. When the temperature of the substrate reached room temperature, the supply of ammonia and nitrogen was stopped, and the GaN substrate was taken out. Without the carbon doped layer, the surface roughness Ra of the obtained GaN film 214 was about 30 nm.
[0042]
Next, in the same manner as in Example 2, an LED structure was formed on the GaN film, and then an electrode was formed to obtain a light emitting diode. A large number of hexagonal pyramidal protrusions were generated on the surface of the obtained LED, and the surface roughness Ra was about 30 nm. The emission center wavelength of the obtained LED was 460 nm. When the light-emitting surface was observed with a microscope, intensity unevenness and color unevenness considered to be dependent on the shape of the protrusions were observed in the surface.
[0043]
Example 3
In this example, the GaN substrate was heat-treated at a high temperature before forming the carbon doped layer. Hereinafter, the process will be described with reference to FIG. The back surface of the GaN substrate produced in the same manner as in Example 1 using the H-VPE method was polished flat using diamond powder and then washed using acetone and ethanol. The substrate 201 was introduced into the MOCVD apparatus, and the substrate temperature was raised to 1000 ° C. over about 15 minutes while flowing hydrogen of 5000 cc / min and ammonia of 3000 cc / min. After the temperature increase, the substrate was heated for about 10 minutes while maintaining the substrate temperature at 1000 ° C. Thereafter, the supply of hydrogen was stopped, and the temperature was lowered to 600 ° C. over about 15 minutes while flowing nitrogen at 5000 cc / min and flowing ammonia at 3000 cc / min. When the temperature reaches 600 ° C., the flow rate of 20 μmol / min of trimethyl gallium (TMG) as a Group 3 element material and carbon tetrabromide (CBr as a carbon material)_Four) Was introduced at a flow rate of 5 μmol / min to form a carbon-doped GaN film 202 with a thickness of about 20 nm. Thereafter, the supply of carbon tetrabromide was stopped, the temperature of the substrate was raised to 1050 ° C., the supply amount of trimethylgallium was increased to 100 μmol / min, and the growth of the GaN film 203 was started continuously. In this way, a GaN film 204 having a thickness of about 4 μm was formed over 1 hour. Next, the supply of trimethylgallium was stopped, and the temperature of the substrate was lowered. When the substrate temperature reached room temperature, the supply of ammonia and nitrogen was stopped, and the GaN film was taken out. The carbon concentration in the carbon-doped GaN film 202 is 1 × 10 as a result of analysis using a secondary ion mass spectrometry (SIMS) apparatus.²⁰cm^-3Met. The reason why the growth temperature of the GaN film doped with carbon is lower than the growth temperature of the GaN film not doped with carbon is that carbon is efficiently doped. In order to increase the growth temperature and dope carbon, it is necessary to increase the amount of carbon tetrabromide introduced. On the other hand, if carbon is doped at a lower growth temperature, the amount of carbon tetrabromide introduced can be reduced.
[0044]
The surface roughness Ra of the obtained GaN film 204 was about 5 nm. The flatness of this surface is good. The GaN film 204 was substantially free from the effects of minute cracks, dislocations, and polishing flaws, and formed a more preferable surface. It was considered that the heat treatment of the GaN substrate in the presence of hydrogen and ammonia caused rearrangement of the outermost surface of the substrate, and cracks and dislocations could almost disappear. This heat treatment can be effectively performed in an atmosphere containing ammonia, and more preferably hydrogen is present. In addition to the disappearance of microcracks and dislocations, it has also been confirmed that propagation of microscopic irregularities existing on the surface of the GaN substrate to the GaN film 204 is suppressed.
[0045]
The effect of the heat treatment of the substrate can be attributed to the rearrangement of atoms on the surface of the substrate at a relatively high temperature to eliminate microcracks, dislocations, irregularities, scratches, and the like. As a result of further experiments, it was found that this effect was obtained by heat treatment at a temperature of 450 to 1100 ° C. Regarding the atmosphere of the heat treatment, an inert gas such as nitrogen may be added to ammonia or a mixture of ammonia and hydrogen. Further, nitrogen may be used instead of hydrogen. However, as the nitrogen concentration increased, the substrate surface tended to become rough. The ammonia concentration is preferably ½ or less of the whole atmosphere, and more preferably 1/10 or less. When the ammonia concentration becomes high, dumpling-like precipitates are easily formed on the substrate surface. On the other hand, when the ammonia concentration is low, nitrogen is easily released from the substrate, and the surface may be roughened.
[0046]
  Example 4
  In this example, the influence of the kind of the intermediate layer containing carbon on the flatness and the light emission characteristics of the obtained light emitting element was investigated. A GaN film having a thickness of about 4 μm was formed on a GaN substrate manufactured by the same method as in Example 1 through an intermediate layer containing carbon having a thickness of 20 nm. The amount of carbon tetrabromide introduced was controlled, and the carbon doping amount in the intermediate layer was 1 × 10 respectively.¹⁹cm^-3And 1 × 10²⁰cm^-3Two types of laminates were obtained. For comparison, a GaN film was grown on the substrate without introducing carbon tetrabromide. As the nitrogen compound semiconductor of the intermediate layer,A1 _xGa_1-xN andIn _yGa_1-yUsing N, the values of x and y are1≧ x ≧ 0,0.35The composition was adjusted by changing within the range of ≧ y ≧ 0. Of these, including carbonIn _y Ga _1-y NWhen manufacturing the film, the growth was performed at 700 ° C. because the composition would be difficult to adjust if the growth temperature was high. Trimethylaluminum (TMA) was used as the A1 raw material, and trimethylindium (TMI) was used as the In raw material. The surface roughness of the finally obtained GaN film was measured, and the relationship between the composition of the intermediate layer containing carbon and the surface roughness was evaluated. The obtained results are shown in FIGS. Referring to FIG. 7, it clearly contains carbonA1 _x Ga _1-x N(1 ≧xWhen the GaN film is grown via ≧ 0), it can be seen that the unevenness of the surface of the GaN film is reduced. However, when the A1 composition ratio exceeds 0.3, the resistance of the intermediate layer itself becomes high, and it becomes difficult to form an electrode under the substrate when forming a light emitting element. Further, when a GaN substrate is used, if the A1 composition ratio of the intermediate layer is increased, cracks or the like may occur in the intermediate layer itself, and dislocations due to the effect of lattice mismatch are likely to occur. Since they extinguish carriers due to light emission, the light emission efficiency of the light emitting element can be lowered. ButTsuIn the middle layerA1 _x Ga _1-x NWhen a light emitting element is formed thereon, the desired A1 composition ratio is 0.3 or less. On the other hand, as shown in FIG.In _y Ga _1-y NIs used, the In composition ratio is 0.35 or less (yIf it is ≦ 0.35), the flatness of the surface is remarkably improved by the action of the intermediate layer. However, as the In composition ratio increases, the surface roughness generally tends to increase, and the effect of the intermediate layer can be reduced. Further, there is a significant correlation between the surface roughness and the light emission unevenness of the obtained light emitting element, and the light emitting element having a large surface roughness tends to increase the light emission unevenness.
[0047]
Example 5
In this example, how the thickness of the intermediate layer affects the surface roughness of the GaN film epitaxially grown thereon, and the surface roughness and light emission characteristics of the light emitting device formed thereon. investigated. GaN or AlN was used for the intermediate layer. The carbon concentration of the intermediate layer is 1 × 10²⁰cm^-3The thickness of the intermediate layer was changed. Similar to the above, intermediate layers having various thicknesses were formed on a GaN substrate, and a GaN film having a thickness of about 4 μm was epitaxially grown thereon. Since the thickness of the intermediate layer increases in proportion to the manufacturing time, the film thickness was controlled by adjusting the manufacturing time. The surface roughness Ra of the obtained laminate was measured. FIG. 9 shows the relationship between the thickness of the GaN film and AlN film, which are intermediate layers, and the surface roughness. In any case of GaN and AlN, the surface roughness of the laminate obtained by providing the intermediate layer is small. In particular, it can be seen that the surface roughness is remarkably reduced when the thickness of the intermediate layer is in the range of 5 nm to 500 Nm. In the same manner as in Example 1, a light emitting element was manufactured and evaluated for light emission characteristics. As a result, there was a significant correlation between the surface roughness and the light emission unevenness of the light emitting element, and a light emitting element with a large surface roughness had a large light emission unevenness. In addition, when a quantum well was used for the light emitting layer, the light emission intensity tended to be strongest and stable especially in the range where the thickness of the intermediate layer was 10 nm to 200 nm or less. In this range, it was speculated that the surface roughness of the nitrogen compound semiconductor light-emitting element formed on the intermediate layer was the smallest, the quantum well was uniformly formed, and the light emission efficiency was improved.
[0048]
Example 6
In this example, the influence of the carbon concentration of the intermediate layer on the surface of the GaN film and the surface and characteristics of the light emitting element was investigated. The following two methods were compared as methods for controlling the carbon concentration in the intermediate layer. One method is a method in which the temperature at which the intermediate layer is formed is kept constant and the amount of addition of bromine tetracarbide as a doping material is changed, and the other method is to change the temperature at which the intermediate layer is formed. In this method, the amount of addition of bromine tetracarbide as a doping material is made constant.
[0049]
First, the former method will be described. The GaN substrate was introduced into the MOCVD apparatus, and the temperature was raised to 700 ° C. over about 15 minutes while flowing nitrogen of 5000 cc / min and hydrogen of 1000 cc / min. At that time, ammonia was introduced at a flow rate of 4000 cc / min when the temperature exceeded 400 ° C. so that GaN was not decomposed by heat. If the temperature is different from 700 ° C., 20 μmol / min of TMG, CBr_FourWere introduced at a flow rate of 0.2 μmol / min to 200 μmol / min, and carbon-doped GaN films with various concentrations were formed to a thickness of about 20 nm. Then CBr_FourThe temperature of the substrate is raised to 1050 ° C., the TMG supply rate is increased to 100 μmol / min, and the GaN film starts to grow continuously. A film was formed. Next, the supply of TMG was stopped, and the temperature of the substrate was lowered. When the temperature of the substrate reached room temperature, the supply of ammonia and nitrogen was stopped, and the GaN substrate was taken out. For comparison, in the above process, CBr_FourA GaN film was grown on the substrate without supplying. About the obtained laminated body, the carbon concentration of the intermediate | middle layer was measured using SIMS. As a result, the carbon concentration of the intermediate layer is determined by adding CBr._Four1 × 10 as the amount increases¹⁸cm^-3~ 1x10^{twenty two}cm^-3There was a tendency to increase in the range. The value below the SIMS detection limit was defined as 0 concentration. FIG. 10 shows the result (701) of measuring the surface roughness of the obtained GaN film.
[0050]
Next, a method of controlling the carbon concentration by changing the temperature at the time of forming the intermediate layer is shown. The GaN substrate was introduced into the MOCVD apparatus, and heated to a temperature of 500 ° C. to 1000 ° C. over a period of about 15 minutes while flowing nitrogen of 5000 cc / min and hydrogen of 1000 cc / min. At that time, ammonia was introduced at a flow rate of 4000 cc / min when the temperature exceeded 400 ° C. so that GaN was not decomposed by heat. When the substrate reaches a set temperature between 500-1000 ° C., 20 μmol / min of TMG, CBr_FourWere introduced at a flow rate of 20 μmol / min, and GaN films doped with carbon at various concentrations were formed to a thickness of about 20 nm. For comparison, CBr_FourOne sample without addition of was also prepared. Then CBr_FourThe substrate temperature was raised to 1050 ° C., the TMG supply amount was increased to 100 μmol / min, and the GaN film was continuously grown. After forming a GaN film having a thickness of about 4 μm over 1 hour, the supply of TMG was stopped and the temperature of the substrate was lowered. When the temperature of the substrate reached room temperature, the supply of ammonia and nitrogen was stopped, and the GaN substrate was taken out. About the obtained laminated body, the carbon concentration in an intermediate | middle layer was measured using SIMS. As a result, the carbon concentration is 1 × 10 as the set temperature during doping is lowered.¹⁸cm^-3~ 1x10^{twenty two}cm^-3There was a tendency to increase in the range. The value below the SIMS detection limit was defined as 0 concentration. The result (702) of measuring the surface roughness of the obtained GaN film is shown in FIG.
[0051]
From FIG. 10, the carbon concentration is 1 × 10.¹⁸cm^-3~ 5x10^{twenty one}cm^-3It can be seen that the flatness of the surface of the obtained GaN film is clearly improved as compared with the case where no carbon is added. Carbon concentration is 5 × 10^{twenty one}cm^-3Above, the surface roughness has increased to the same extent as that without carbon doping. This is presumably because the impurity concentration was too high and the crystallinity of the GaN film itself was impaired. Comparing curve 701 and curve 702 in FIG. 10, it can be seen that these tendencies do not depend on the growth temperature of the intermediate layer, but depend only on the carbon concentration.
[0052]
About the obtained laminated body, the light emitting element was produced similarly to Example 2, and the light emission characteristic was evaluated. As a result, there was a significant correlation between the unevenness of the surface and the light emission unevenness of the light emitting element, and the light emission element having a large surface unevenness had a large light emission unevenness.
[0053]
In the series of examples described above, thick GaN produced by the H-VPE method was used as the substrate. However, the present invention can achieve the same effect with a GaN substrate having a thickness exceeding 20 μm, which is manufactured by using another method such as MOCVD. In addition, as long as it is a single crystal film, not only GaN but also other nitrogen compound semiconductors such as AlN may be used. Further, as impurities in the nitrogen compound semiconductor substrate, silicon (Si), oxygen (O), magnesium (Mg), hydrogen (H), chlorine (C1), bromine (Br), zinc (Zn), arsenic (As) , Phosphorus (P), selenium (Se) and the like may be contained.
[0054]
Example 7
In this example, a laser diode was fabricated on a GaN substrate via a carbon-doped GaN film. Hereinafter, the process will be described with reference to FIG. A GaN thick film was grown on the sapphire substrate by the H-VPE method in the same manner as in Example 1, and then both surfaces of the obtained thick film were polished to produce a GaN substrate 102. During the thick film growth, 5 × 10 5 of silicon (Si) is used as an impurity in order to give the substrate n-type conductivity.¹⁸cm^-3It added so that it might become the density | concentration of. Dichlorosilane (SiH diluted with nitrogen to 100 ppm as a material for adding Si₂C1₂) And introducing this during growth at about 100 cc / min, it was possible to add Si at the above concentration. The obtained GaN substrate 102 was introduced into an MOCVD apparatus, and then 1 × 10 having a thickness of 20 nm in the same manner as in Example 1.²⁰cm^-3A GaN film 103 containing carbon at a concentration of 800 ° C. was formed. Thereafter, the temperature is raised to 1050 ° C., and subsequently Si is 1 × 10 6.¹⁸cm^-3An n-type GaN film 104 having a concentration of 3 μm was formed. As a means for adding Si, monosilane diluted with hydrogen to 100 ppm (SiH_Four) And introduced at 10 cc / min during growth, it was possible to add Si at the above concentration. Next, in order to lower the growth temperature to 800 ° C. and reduce cracks, In doped with Si at a thickness of 50 nm._0.05Ga_0.95The N film 105 is grown, and then the growth temperature is raised again to 1050 ° C. to form an n-type cladding layer 106 with a 0.7 μm thick Si-doped n-type A1._0.1Ga_0.9N was deposited. Trimethylindium (TMI) was used as the In raw material, and trimethylaluminum (TMA) was used as the Al raw material. After the growth of the n-type cladding layer 106, an n-type GaN optical guide layer 107 having a thickness of 0.1 μm is grown, and the growth temperature is lowered to 750 ° C._0.05Ga_0.95N / In_0.18Ga_0.82A light emitting layer 108 made of N was grown. The growth temperature was raised again to 1050 ° C., and the 30 nm thick A1_0.2Ga_0.8Carrier block layer 109 made of N, 1 × 10 doped with Mg¹⁸cm^-30.1 μm-thick p-type GaN optical guide layer 110 having a p-type carrier, 0.5 μm-thick Mg-doped p-type A1_0.1Ga_0.9An N-cladding layer 111 and a 0.1 μm-thick Mg-doped p-type GaN contact layer 114 were grown. Bisethylcyclopentadienylmagnesium (EtCp2Mg) was used as a material for adding Mg. As in Example 1, the temperature was lowered to room temperature, and the production of the composite film having a laser layer structure was completed. In the obtained laser structure, the surface roughness Ra of the uppermost layer was about 5 nm. About the obtained laser layer structure, a p-type contact layer and a part of the p-type cladding layer were etched by photolithography and reactive ion etching to form a ridge having a width of 3 μm. After that, SiO as an insulating film₂The film 112 was partially coated to form a p-type contact electrode 113 made of Au / Pd, and an n-type contact electrode 101 made of Al was formed on the back surface of the substrate 102. Cleavage was performed to obtain a cavity length of about 500 μm, and a laser element was obtained. The obtained laser element had a threshold voltage of 6 V and a threshold current of 50 mA. For comparison, a laser structure was obtained by directly forming a laser structure on a GaN substrate without using a GaN film containing carbon by the method described above. The surface roughness Ra of the outermost layer in the obtained laser structure was 20 nm. The obtained laser device has a threshold voltage of 6 V, which is almost the same value as that having a carbon-doped intermediate layer. However, its threshold current is 80 mA, which is higher than that with a carbon-doped interlayer. The reason why the threshold current is increased is that the surface roughness of the laser structure film is increased, the dispersion of light propagating inside the laser element is increased, and the flatness of the film is decreased. It is considered that a distribution occurs in the emission intensity and wavelength of the light, resulting in uneven emission.
[0055]
For the light emitting diode (LED), the flatness of the diode surface could be improved by forming the intermediate layer. Then, the emission intensity distribution and emission wavelength distribution in the light emitting surface were reduced. In the case of a light emitting diode, if there is unevenness in particular, a difference in emission wavelength of 5 nm or more occurs between the convex part and the concave part. By improving the flatness of the surface, the light emission efficiency was increased and the half width of the wavelength was narrowed.
[0056]
Example 8
In the above embodiment, a free-standing GaN substrate obtained by removing the sapphire substrate was used. However, in order to improve the surface roughness, a free-standing substrate is not essential as the first crystal layer. For example, as shown in FIG. 12, a 20 μm-thick GaN substrate layer 102 was formed on sapphire 116, and a laminated structure was formed thereon by the same method as in Example 7 to obtain a laser element. In this structure, since the n-electrode cannot be provided on the GaN substrate layer 102, etching is performed from the surface to the n-type GaN film 104 by reactive ion etching, and A1 is deposited on the exposed n-type GaN film 104. Thus, an n-type contact electrode 101 was formed. The threshold voltage and threshold current of the obtained laser element were almost the same as those of the laser element of Example 7.
[0057]
Example 9
An optical pickup system was configured using the semiconductor laser obtained in Example 7. As a laser using a nitrogen compound semiconductor, the used laser was able to form a far-field image and a near-field image with stable characteristics because the emission intensity distribution in the device was small. The optical pickup system using the laser according to the present invention showed better characteristics in reading accuracy and writing accuracy than the optical pickup system using the conventional nitrogen compound semiconductor laser. The optical pickup according to the present invention can be preferably used for recording and reproduction of recording media such as CDs, CD-Rs and CD-R-RWs of personal computers, and recording media such as game machines, movies and digital video disks. .
[0058]
【The invention's effect】
According to the present invention, the flatness of the surface of the nitrogen compound semiconductor element can be improved. In addition, a light-emitting element such as a semiconductor laser or a light-emitting diode using the present invention can reduce the threshold current, and thus can exhibit stable characteristics. Further, in the light emitting device using the present invention, the intensity and wavelength distribution in the light emitting surface can be reduced. If the laser element according to the present invention is used in an optical pickup system, its reading and writing accuracy can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a specific example of a nitrogen compound semiconductor laminate according to the present invention.
FIG. 2 is a SIMS analysis chart showing a carbon concentration distribution of an intermediate layer in the nitrogen compound semiconductor laminate according to the present invention.
FIG. 3 is a schematic diagram showing a process for defining the thickness of an intermediate layer from a SIMS analysis chart.
FIG. 4 is a schematic cross-sectional view showing a process for manufacturing a nitrogen compound semiconductor laminate according to the present invention.
FIG. 5 is a schematic cross-sectional view showing a specific example of a light emitting device according to the present invention.
FIG. 6 is a schematic cross-sectional view showing a conventional film forming process.
FIG. 7 is a diagram showing the relationship between the Al composition ratio of the intermediate layer and the surface roughness of the resulting structure.
FIG. 8 is a diagram showing the relationship between the In composition ratio of the intermediate layer and the surface roughness of the resulting structure.
FIG. 9 is a diagram showing the relationship between the thickness of the intermediate layer and the surface roughness of the resulting structure.
FIG. 10 is a diagram showing the relationship between the carbon concentration of the intermediate layer and the surface roughness of the resulting structure.
FIG. 11 is a schematic cross-sectional view showing a specific example of a semiconductor laser according to the present invention.
FIG. 12 is a schematic cross-sectional view showing another specific example of a semiconductor laser according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Nitrogen compound semiconductor laminated body, 11 1st crystal layer, 12 Intermediate layer, 13 2nd crystal layer, 101 n contact electrode, 102 Nitrogen compound semiconductor substrate, 103 Nitrogen compound semiconductor film containing carbon, 104 n-type GaN film , 105 IN_0.05Ga_0.95N crack prevention layer, 106 n-type A1_0.1Ga_0.9N clad layer, 107 n-type GaN light guide layer, 108 IN_0.05Ga_0.95N / In_0.18Ga_0.82Light emitting layer made of N, 109 A1_0.2Ga_0.8N carrier block layer, 110 p-type GaN light guide layer, 111 p-type A1_0.1Ga_0.9N clad layer, 112 SiO₂Insulating film, 113 p-type contact electrode, 114 p-type GaN contact layer.

Claims (13)

A first crystal layer comprising a GaN substrate ;
An intermediate layer formed directly on the first crystal layer and made of a nitrogen compound semiconductor containing carbon as an impurity, and having a thickness of 5 nm to 500 nm; and formed directly on the intermediate layer and made of a nitrogen compound semiconductor A second crystal layer comprising:
A nitrogen compound semiconductor laminate, wherein the nitrogen compound semiconductor of the intermediate layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.3). A first crystal layer comprising a GaN substrate ;
An intermediate layer formed directly on the first crystal layer and made of a nitrogen compound semiconductor containing carbon as an impurity, and having a thickness of 5 nm to 500 nm; and formed directly on the intermediate layer and made of a nitrogen compound semiconductor A second crystal layer comprising:
The nitrogen compound semiconductor stack according to claim 1, wherein the nitrogen compound semiconductor of the intermediate layer is In _y Ga _1-y N (0 ≦ y ≦ 0.35).   The nitrogen compound semiconductor laminate according to claim 1, wherein the intermediate layer has a thickness of 10 nm to 200 nm. 4. The nitrogen compound semiconductor stack according to claim 1, wherein a concentration of the carbon in the intermediate layer is 5 × 10 ¹⁸ cm ⁻³ or more and 5 × 10 ²¹ cm ⁻³ or less. object. The second crystal layer, characterized in that an epitaxial growth layer, a nitrogen compound semiconductor multilayer structure according to any one of claims 1-4. 6. The nitrogen compound semiconductor laminate according to claim 5 , which is an epitaxial wafer for forming an element thereon. The nitrogen compound semiconductor laminate according to claim 6 , wherein the second crystal layer has a surface roughness Ra of 30 nm or less. The nitrogen compound semiconductor laminate according to any one of claims 1 to 5 ,
A laminate structure formed on the second crystal layer and made of a nitrogen compound semiconductor for generating optical output from electric power, and an electrode for supplying electric power to the laminate structure, A light emitting element. The light emitting device according to claim 8 , wherein the light emitting device is a semiconductor laser. An optical pickup system comprising the light emitting element according to claim 9 as an apparatus for supplying light to an optical system. On the first crystal layer made of the GaN substrate , the thickness is 5 nm made of a nitrogen compound semiconductor containing carbon as an impurity from a carbon source, a Group 3 element source in the periodic table, and a nitrogen source. The first step of forming an intermediate layer having a thickness of 500 nm or less, and the supply of the carbon supply source are stopped, and the group 3 element supply source and nitrogen in the periodic table are continuously supplied to the first step. A second step of forming a second crystal layer made of a nitrogen compound semiconductor from a supply source of
A method for producing a nitrogen compound semiconductor laminate, wherein the nitrogen compound semiconductor of the intermediate layer is Al _x Ga _1-x N (0 ≦ x ≦ 0.3). On the first crystal layer made of the GaN substrate , the thickness is 5 nm made of a nitrogen compound semiconductor containing carbon as an impurity from a carbon source, a Group 3 element source in the periodic table, and a nitrogen source. The first step of forming an intermediate layer having a thickness of 500 nm or less, and the supply of the carbon supply source are stopped, and the group 3 element supply source and nitrogen in the periodic table are continuously supplied to the first step. A second step of forming a second crystal layer made of a nitrogen compound semiconductor from a supply source of
The method for producing a nitrogen compound semiconductor laminate, wherein the nitrogen compound semiconductor of the intermediate layer is In _y Ga _1-y N (0 ≦ y ≦ 0.35). The manufacturing method according to claim 11 or 12 , wherein the first step and the second step are performed by metal organic vapor phase epitaxy.

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