JP4788138B2 - Nitride semiconductor device - Google Patents

Description

  The present invention relates to a light emitting device such as a light emitting diode (LED) and a semiconductor laser diode (LD), or an element made of a nitride semiconductor used for a light receiving device such as a photodiode.

Nitride semiconductors have a wide band gap energy ranging from the ultraviolet to the visible range, and are useful as semiconductor materials for light emitting / receiving devices. A nitride semiconductor is typically represented by a general formula of Al _X In _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1). Nitride semiconductor devices using nitride semiconductors therefore have light emission in a wide wavelength region from a relatively short wavelength ultraviolet region to a visible light region including red, and are widely used as devices constituting LEDs and LDs. It is used. In recent years, miniaturization, long life, high reliability, and high output have progressed, and they are mainly used for electronic devices such as personal computers and DVDs, medical devices, processing devices, and optical fiber communication light sources. A nitride semiconductor layer constituting such a nitride semiconductor element is formed by epitaxial growth, but there is no high-quality large-sized GaN single crystal substrate that can serve as a base substrate. Therefore, different types of substrates different from nitride semiconductors such as sapphire and SiC have been conventionally used as the base substrate. For example, when making a light emitting diode or a semiconductor laser including a highly mixed crystal AlGaN layer with a high Al composition ratio, GaN is formed on a substrate such as sapphire by using metal organic chemical vapor deposition (MOCVD). A GaN-ELO substrate obtained by growing GaN on the substrate by ELO (epitaxial laterally overgrowth) has been used as a base substrate by heteroepitaxial technology for growth. As shown in FIG. 1, an InGaN layer 12 is grown on the ELO substrate 11 as a buffer layer (buffer layer) for preventing the occurrence of cracks, and an AlInGaN element 13 is further grown thereon to manufacture a nitride semiconductor element. is doing. According to this method, an increase in dislocations in the regrowth of the nitride semiconductor on the ELO substrate can be suppressed, cracks can be effectively prevented, crystallinity can be improved, and good electrical characteristics can be obtained. .
JP 2002-316893 A

  On the other hand, in place of such an ELO substrate, there is a strong demand for realizing a high-quality, large-area nitride semiconductor wafer, particularly a free-standing wafer (self-standing wafer). A free-standing nitride semiconductor wafer is a wafer mainly composed of a nitride semiconductor without a support substrate such as sapphire, GaAs, or SiC. In particular, sapphire has a large difference in lattice constant and thermal expansion coefficient from that of nitride semiconductors. Therefore, the epitaxial growth layer on such a heterogeneous substrate has a problem of generating dislocations and stresses at the interface, and has a large dislocation density. Realization of a GaN single crystal substrate is expected. In general, in order to obtain a free-standing nitride semiconductor wafer, a method is used in which a nitride semiconductor film is epitaxially grown on a substrate made of a material different from that of the nitride semiconductor, and then the substrate is removed. As such a free standing wafer, a free standing GaN substrate having no sapphire substrate (Free-Standing-GaN) has been developed. In the free-standing GaN substrate, a GaN substrate layer is grown using a heterogeneous substrate such as a sapphire substrate as a base substrate, and then the base substrate is removed by polishing, etching, or the like to make only the GaN substrate. For this reason, it is necessary to correct the distortion of the substrate and to flatten the surface, and the surface is polished by a CMP (Chemical Mechanical Polishing) process or the like. Therefore, when a GaN layer is grown and used on a sapphire substrate, the grown surface becomes the surface as it is, whereas in a free-standing GaN substrate, the surface is temporarily polished after the GaN substrate layer is grown and then regrown. It will be. However, when such a free-standing GaN substrate 21 is used to grow a nitride semiconductor element including an AlInGaN element 23 having the same configuration as described above via the InGaN buffer layer 22 as shown in FIG. Unlike growth on ELO substrates, it has been found that a clear increase in crystal defects occurs. Such an increase in crystal defects greatly affects the electrical characteristics and becomes a major factor that causes deterioration of the device.

  The present invention has been made to solve such problems. The main object of the present invention is to improve the electrical characteristics of a nitride semiconductor device grown on a freestanding GaN substrate.

In order to achieve the above object, a nitride semiconductor device according to the first aspect of the present invention includes a free-standing substrate made of GaN, and n-Al _x Ga _1-x N (0 < a first buffer layer made of x ≦ 0.05 ), a second buffer layer made of n-In _y Ga _1-y N (0 <y ≦ 0.1) formed on the first buffer layer, 2 includes an n-AlGaN layer which is formed in the buffer layer, the first buffer layer and second buffer layer that are in contact. With this configuration, the function of the buffer layer is divided into a first buffer layer that suppresses the occurrence of dislocations from the regrowth interface and a second buffer layer that suppresses the occurrence of cracks, thereby achieving high quality on the free-standing substrate. A nitride semiconductor device having excellent electrical characteristics can be obtained by growing the AlGaN layer.

  Furthermore, in the nitride semiconductor device according to the second aspect of the present invention, the thickness of the first buffer layer can be made thinner than the thickness of the second buffer layer. With this configuration, the occurrence of cracks by the first buffer layer can be suppressed.

  Furthermore, in the nitride semiconductor device according to the third aspect of the present invention, the thickness of the first buffer layer can be 300 to 3000 Å, and the thickness of the second buffer layer can be 500 to 4000 Å. With this configuration, the occurrence of cracks by the first buffer layer can be suppressed.

  Furthermore, in the nitride semiconductor device according to the fourth aspect of the present invention, the Si concentration of the first buffer layer can be made lower than the Si concentration of the second buffer layer. With this configuration, it is possible to prevent a decrease in crystal quality during the growth of the second buffer layer.

Furthermore, in the nitride semiconductor device according to the fifth aspect of the present invention, the Si concentration of the first buffer layer is 0.3 × 10 ^{18 to} 3.0 × 10 ¹⁸ cm ⁻³ , and the second buffer layer The Si concentration can be set to 1 × 10 ^{18 to} 5 × 10 ¹⁸ cm ⁻³ . With this configuration, it is possible to prevent a decrease in crystal quality during the growth of the second buffer layer.

  Furthermore, in the nitride semiconductor device according to the sixth aspect of the present invention, the Al composition ratio of the AlGaN layer can be 0.05 or more.

  Furthermore, in the nitride semiconductor device according to the seventh aspect of the present invention, the substrate is a free-standing GaN substrate doped with Si or O.

  Furthermore, in the nitride semiconductor device according to the eighth aspect of the present invention, the substrate is a substrate whose surface is processed smoothly.

Furthermore, the nitride semiconductor device according to the ninth aspect of the present invention includes a gallium nitride serving as a support substrate, a first buffer layer made of n-type gallium nitride containing Al on the substrate, and the first buffer layer. a second buffer layer is n-type gallium nitride containing in on, and an n-type gallium nitride containing Al in the second buffer layer, the first buffer layer and second buffer layer is that in contact . With this configuration, the function of the buffer layer is divided into a first buffer layer that suppresses the occurrence of dislocations from the regrowth interface and a second buffer layer that suppresses the occurrence of cracks, thereby achieving high quality on the free-standing substrate. By growing gallium nitride containing Al, a nitride semiconductor device having excellent electrical characteristics can be obtained.
The nitride semiconductor device according to another aspect is characterized in that an active layer and a p-AlGaN layer are sequentially formed on an n-AlGaN layer or an n-type gallium nitride containing Al.

  According to the nitride semiconductor device of the present invention, by dividing the buffer layer into a plurality of layers, it is possible to effectively prevent the occurrence of dislocation from the regrowth interface and suppress the occurrence of cracks. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a nitride semiconductor element for embodying the technical idea of the present invention, and the present invention does not specify the nitride semiconductor element as follows. Further, the present specification by no means specifies the members shown in the claims to the members of the embodiments. In particular, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the embodiments are not intended to limit the scope of the present invention unless otherwise specified, and are merely explanations. It is just an example. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, in the following description, the same name and symbol indicate the same or the same members, and detailed description thereof will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing.

  FIG. 3 is a schematic cross-sectional view showing the configuration of the nitride semiconductor device according to one embodiment of the present invention. The nitride semiconductor device shown in this figure includes a free-standing GaN substrate 31, n-AlGaN that is a first buffer layer 32 formed on the substrate, and a second buffer layer 34 formed on the first buffer layer 32. N-InGaN and an AlInGaN element 36 formed on the second buffer layer 34. Thus, by combining layers having different compositions for each function of the buffer layer, it is possible to achieve a dislocation propagation and a crack prevention function, and to grow a high-quality AlInGaN element 36, thereby producing a nitride semiconductor element having excellent electrical characteristics. Obtainable. Since the lifetime characteristic of an optical element using a semiconductor depends on the crystallinity of the active layer including the dislocation density, it is necessary to reduce dislocations as much as possible. The occurrence of cracks also has an adverse effect on the device. For example, if a fine crack is generated in an n-type contact layer formed on a GaN substrate, there is a possibility that a threshold value is increased or a life characteristic is decreased in the case of a laser element. Therefore, preventing the occurrence of cracks and dislocations is important for device reliability.

  The free-standing GaN substrate 31 is preferably doped with Si or O. In order to smooth the surface, the surface is processed by CMP treatment or polishing. In general, when a free-standing GaN substrate is used, an InGaN buffer layer is grown on the substrate in order to prevent cracks from being generated from the GaN substrate, as shown in FIG. However, when regrowth is performed from the InGaN buffer layer, dislocation occurs, and a trace that seems to be a scratch when the GaN substrate is polished remains. This is presumably because the scratches caused by processing the surface of the freestanding GaN substrate by polishing or the like cannot be eliminated by the InGaN buffer layer. Thus, it has been found that by further interposing an AlGaN layer between the InGaN layer and the GaN substrate, the occurrence of the above dislocations can be suppressed and the occurrence of cracks can also be prevented.

The first buffer layer 32 is made of n-Al _x Ga _1-x N (0 < x ≦ 0.05), and mainly suppresses the occurrence of dislocations from the regrowth interface with the free-standing GaN substrate 31. The first buffer layer 32 is preferably doped with a dopant such as Si. The doping amount of the dopant is adjusted so that the Si concentration is 0.3 × 10 ^{18 to} 3.0 × 10 ¹⁸ cm ⁻³ . The thickness of the first buffer layer 32 is preferably 300 to 3000 angstroms. The x value is preferably 0.03 or less because cracks are less likely to occur.

On the other hand, the second buffer layer 34 is made of n-In _y Ga _1-y N (0 <y ≦ 0.1) and mainly functions as a crack prevention layer. The second buffer layer 34 is also preferably doped with a dopant such as Si, and the doping amount is adjusted so that the Si concentration is 1 × 10 ^{18 to} 5 × 10 ¹⁸ cm ⁻³ . The thickness of the second buffer layer 34 is preferably 500 to 4000 angstroms. This can prevent the crystal quality of the second buffer layer growth from deteriorating. In addition, by making y value 0.03 or more, it can make it harder to generate | occur | produce a crack, and crystallinity can be improved more by making it 0.08 or less.

The first buffer layer 32 is preferably thinner than n-In _y Ga _1-y N (0 <y ≦ 0.1), which is the second buffer layer 34. By using an AlGaN layer instead of the InGaN layer as the first buffer layer 32, the occurrence of cracks increases. In order to prevent the increase of the crack, it is conceivable to increase the In mixed crystal ratio of the second buffer layer 34 or to increase the film thickness of the second buffer layer 34. Any increase in the thickness of the InGaN layer is undesirable because it leads to a decrease in crystallinity of the InGaN layer. In order to solve this problem, the occurrence of cracks is suppressed by making the thickness of the first buffer layer 32 relatively smaller than that of the second buffer layer 34. By suppressing the film thickness of the second buffer layer 34, it contributes to the improvement of mass production efficiency while fulfilling the function as a buffer layer. Similarly, the crystal concentration of the InGaN layer can be prevented from being lowered by making the Si concentration of the first buffer layer 32 lower than the Si concentration of the second buffer layer 34.

  As described above, an increase in cracks caused by adding the InGaN buffer layer as the first buffer layer can be suppressed by reducing the Si doping amount and the film thickness of the first buffer layer. In addition, the effect of suppressing dislocations and cracks can be maximized without increasing the In mixed crystal ratio of the second buffer layer. This eliminates the problem of growing an AlInGaN device using a free-standing GaN substrate, and a nitride semiconductor device having excellent electrical characteristics can be obtained. The AlInGaN element 36 is a semiconductor element including an AlGaN layer as an n-side cladding layer or the like. The AlGaN layer can be a highly mixed crystal with a high Al composition ratio, for example, the Al composition ratio can be 0.05 or more.

In order to confirm the effect of the above configuration, a CL (cathode luminescence) micrograph of a highly mixed crystal AlGaN layer grown with the configuration of FIG. 3 is shown in FIG. As a comparative example, a highly mixed crystal AlGaN layer grown through an InGaN buffer layer using a sapphire substrate in the configuration of FIG. 1 and a free standing GaN substrate grown through an InGaN buffer layer in the configuration of FIG. CL micrographs of the highly mixed crystal AlGaN layer are shown in FIGS. 5 and 6, respectively. In these figures, black portions indicate the occurrence of dislocations. As is apparent from the figure, in the configuration of the present embodiment, almost no dislocation is observed, whereas in the case of the sapphire substrate, the occurrence of dislocation is confirmed in the form of vertical stripes, and the InGaN buffer layer is formed on the free-standing GaN substrate. Even in the example using, spot-like dislocations were confirmed as a whole. From this, the superiority of the configuration in which the buffer layer is divided into two layers was confirmed.
(Nitride semiconductor device manufacturing method)

A nitride semiconductor element including a highly mixed crystal AlGaN layer grown as described above can be used to produce a light emitting element or a light receiving element such as an LED or LD. Next, as a first embodiment, a method for manufacturing a nitride semiconductor laser element oscillating at 445 nm shown in the schematic cross-sectional view of FIG. An n-type doped GaN substrate 101 is set in a MOVPE reaction vessel, TMA (trimethylaluminum), trimethylgallium (TMG), ammonia (NH ₃ ) is used, silane gas (SiH ₄ ) is used as an impurity gas, Si is used. A first buffer layer 102 made of n-Al _0.02 Ga _0.98 N doped with 0.8 × 10 ¹⁸ / cm ³ is grown to a thickness of 1000 Å. After growing the first buffer layer, the temperature is raised and TMI (trimethylindium), TMG, ammonia is used, silane gas is used as impurity gas, and Si is doped at 3 × 10 ¹⁸ / cm ^3, and n-In _y Ga _1-y N A second buffer layer 103 is grown to a thickness of 1500 angstroms.

Next, using TMA, TMG, and ammonia, a layer made of undoped Al _0.16 Ga _0.84 N is grown at 1050 ° C. to a thickness of 25 Å, then TMA is stopped, silane gas is allowed to flow, and Si is supplied at 1 × 10 ¹⁹ / A layer made of cm ³ -doped n-type GaN is grown to a thickness of 25 Å. These layers are alternately stacked to form a superlattice layer, and an n-side cladding layer 104 made of a superlattice having a total thickness of 1.2 μm is grown. Here, in the grown n-side cladding layer 104, no fine cracks are generated, and the generation of cracks is well prevented. Further, even if a fine crack or scratch is generated on the GaN substrate, the propagation of the crack can be prevented by growing the first and second buffer layers, and an element structure with good crystallinity can be grown. In this embodiment, the thickness of the AlGaN first buffer layer is made thinner than that of the InGaN second buffer layer, thereby preventing an increase in cracks without increasing the In composition ratio.

Next, using TMG and ammonia as source gases, an n-type light guide layer 105 made of undoped GaN is grown at a temperature of 1050 ° C. to a thickness of 750 Å. Next, the temperature is set to 880 ° C., TMI, TMG, and ammonia are used as source gases, silane gas is used as an impurity gas, and a barrier layer made of In _0.01 Ga _0.99 N doped with Si at 5 × 10 ¹⁸ / cm ^{3 is} added. Grow with angstrom thickness. Subsequently, the temperature is lowered to 820 ° C., the silane gas is stopped, and a well layer made of undoped In _0.3 Ga _0.7 N is grown to a thickness of 50 Å. Further, using TMA at the same temperature, an intermediate layer made of Al _0.3 Ga _0.7 N is grown to a thickness of 10 Å. The three-layer structure of the barrier layer, the well layer, and the intermediate layer is repeatedly laminated twice, and finally the barrier layer is formed to grow the active layer 106 composed of multiple quantum wells (MQW) with a total thickness of 580 angstroms. Let

Next, the TMI is stopped, Cp ₂ Mg is allowed to flow, and a p-side cap layer 107 made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown to a thickness of 100 Å. Subsequently, Cp ₂ Mg and TMA are stopped, and a p-side light guide layer 108 made of undoped GaN is grown to a thickness of 0.1 μm at 1050 ° C. The p-side light guide layer 108 is grown as undoped, but due to the diffusion of Mg from the p-side cap layer 107, the Mg concentration becomes 5 × 10 ¹⁶ / cm ³ and exhibits p-type. Subsequently, Cp ₂ Mg is stopped, TMA is flown, and a layer made of undoped Al _0.2 Ga _0.8 N is grown at a thickness of 25 Å at 1050 ° C. Then, TMA is stopped, Cp ₂ Mg is flowed, and the Mg concentration is 1 A layer made of undoped GaN composed of × 10 ¹⁹ / cm ³ is grown to a thickness of 25 Å, and a p-side cladding layer 109 made of a superlattice layer having a total thickness of 0.6 μm is grown. Finally, a p-side contact layer 110 made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown on the p-side cladding layer 109 to a thickness of 150 Å.

The wafer on which the nitride semiconductor has been grown as described above is taken out of the reaction vessel, and SiO _{2 made} of stripes having a width of 2.3 μm is formed on the surface of the uppermost p-side contact layer 110 through a mask having a predetermined shape. A protective film made of is produced. After forming the protective film, etching is performed up to the vicinity of the interface between the p-side cladding layer 109 and the p-side light guide layer 108 using RIE (reactive ion etching) as shown in FIG. The waveguide is formed.

After forming the striped waveguide, an insulating film made of ZrO ₂ is formed on the surface of the nitride semiconductor layer with the SiO ₂ mask attached. After forming the insulating film, it is immersed in buffered hydrofluoric acid to dissolve and remove SiO ₂ formed on the p-side contact layer 110, and ZrO ₂ on the p-side contact 110 layer is removed together with SiO ₂ by a lift-off method. . Next, a SiO ₂ mask is formed on the ridge surface, and etching is performed by RIE to expose the surface of the n-type free standing substrate 101. Next, a p-side ohmic electrode 120 made of Ni and Au is formed in a stripe pattern on the ridge outermost surface of the p-side contact layer 110. On the other hand, the n-side ohmic electrode 122 made of Ti and Al is formed in a stripe shape on the surface of the n-type free standing substrate 101 exposed previously. Next, as shown in FIG. 7, an insulating film 130 made of SiO ₂ is formed on the surface of the nitride semiconductor layer exposed between the p-side ohmic electrode 120 and the n-side ohmic electrode 122, and the insulating film 130 is interposed therebetween. Then, the p-side pad electrode 121 electrically connected to the p-side ohmic electrode 120 and the n-side pad electrode 123 electrically connected to the n-side ohmic electrode 122 are formed.

  As described above, after forming both the p and n pad electrodes, the GaN is cleaved on the M surface of the nitride semiconductor GaN substrate (the surface corresponding to the side surface of the hexagonal column when the nitride semiconductor is represented by a hexagonal column). The wafer is made into a bar shape, and a resonance surface is produced on the cleavage surface of the bar. After producing the resonance surface, a bar-shaped wafer was further cut in a direction perpendicular to the resonance surface to obtain a laser chip.

Next, when each electrode was wire-bonded and laser oscillation was attempted at room temperature, decomposition of In could be suppressed, a sharp emission peak was obtained, threshold current density at room temperature was 2.0 kA / cm ² , oscillation wavelength A continuous oscillation of 450 nm was confirmed, and the lifetime was 1000 hours or more. Also, the threshold voltage could be greatly reduced to 4.0V.

Next, as a second embodiment, a method of manufacturing a nitride semiconductor laser element that oscillates in the UV region, which includes a larger number of highly mixed crystal AlGaN layers and which is a major problem in suppressing cracks, will be described. A schematic cross-sectional view of the manufactured nitride semiconductor laser device is shown in FIG. An n-type doped GaN substrate 201 is set in a MOVPE reaction vessel, TMA (trimethylaluminum), trimethylgallium (TMG), ammonia (NH ₃ ) is used, silane gas (SiH ₄ ) is used as impurity gas, Si is used. A first buffer layer 202 made of n-Al _0.02 Ga _0.98 N doped with 0.8 × 10 ¹⁸ / cm ³ is grown to a thickness of 1000 Å. After growing the first buffer layer, the temperature is raised and TMI (trimethylindium), TMG, ammonia is used, silane gas is used as impurity gas, and Si is doped at 3 × 10 ¹⁸ / cm ^3, and n-In _y Ga _1-y N A second buffer layer 203 is grown to a thickness of 1500 angstroms.

Next, an n-side cladding layer 204 made of Al _0.11 Ga _0.89 N doped with Si at 1 × 10 ¹⁸ / cm ³ is grown to a thickness of 0.7 μm using ammonia, TMG, and silane gas as an impurity gas. Here, no fine cracks are generated in the grown n-side cladding layer 204, and the propagation of cracks is effectively prevented by growing the first and second buffer layers as in the first embodiment. An element structure with good crystallinity could be grown. Also in this embodiment, the thickness of the AlGaN first buffer layer is made thinner than that of the InGaN second buffer layer, and the increase of cracks is prevented without increasing the In composition ratio.
Next, TMG and ammonia are used as source gases, and an n-type light guide layer 205 made of undoped Al _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm at the same temperature. Next, a barrier layer made of Al _0.15 Ga _0.85 N doped with 5 × 10 ¹⁸ / cm ^{3 of} Si using TMI, TMG and ammonia as source gases, silane gas as impurity gas, and temperature of 950 ° C. Grow with angstrom thickness. Subsequently, the silane gas is stopped, and a well layer made of undoped In _0.01 Ga _0.09 N is grown to a thickness of 100 Å. Further, using TMA at the same temperature, a barrier layer made of Al _0.15 Ga _0.85 N is grown to a thickness of 50 Å to grow an active layer 206 made of a single quantum well (SQW).

Next, TMI is stopped, Cp ₂ Mg is allowed to flow, and a p-side cap layer 207 made of p-type Al _0.30 Ga _0.70 N doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown to a thickness of 100 Å. Subsequently, Cp ₂ Mg and TMA are stopped, and a p-side light guide layer 208 made of undoped Al _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm at 1050 ° C. The p-side light guide layer 208 is grown as undoped, but due to the diffusion of Mg from the p-side cap layer 207, the Mg concentration becomes 5 × 10 ¹⁶ / cm ³ and exhibits p-type. Subsequently, Cp ₂ Mg is stopped, TMA is flown, and a layer made of undoped Al _0.13 Ga _0.87 N is grown at a thickness of 25 Å at 1050 ° C., followed by flow of Cp ₂ Mg, and the Mg concentration is 1 × 10 ¹⁹ / A layer made of Al _0.09 Ga _0.91 N made of cm ³ is grown to a thickness of 25 Å, and a p-side cladding layer 209 made of a superlattice layer having a total thickness of 0.6 μm is grown. Finally, a p-side contact layer 210 made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown on the p-side cladding layer 209 to a thickness of 150 Å.

The wafer on which the nitride semiconductor has been grown as described above is taken out of the reaction vessel, and SiO _{2 made} of stripes having a width of 2.3 μm is formed on the surface of the uppermost p-side contact layer 210 through a mask having a predetermined shape. A protective film made of is produced. After forming the protective film, etching is performed to the vicinity of the interface between the p-side cladding layer 209 and the p-side light guide layer 208 using RIE (reactive ion etching) as shown in FIG. 7, and a stripe shape having a width of 2.3 μm. The waveguide is formed.

After forming the stripe waveguide, an insulating film 230 made of ZrO ₂ is formed on the surface of the nitride semiconductor layer with the SiO ₂ mask attached. After forming the insulating film, it is immersed in buffered hydrofluoric acid to dissolve and remove SiO ₂ formed on the p-side contact layer 210, and ZrO ₂ on the p-side contact 210 layer is removed together with SiO ₂ by a lift-off method. . Next, a p-side ohmic electrode 220 made of Ni and Au is formed in a stripe pattern on the ridge outermost surface of the p-side contact layer 210. Next, a p-side pad electrode 221 electrically connected to the p-side ohmic electrode 220 is formed. Next, an n-side ohmic electrode and pad electrodes 222 and 223 are formed on the back surface of the n-type free standing substrate 201.

  As described above, after forming both the p and n pad electrodes, the GaN is cleaved on the M surface of the nitride semiconductor GaN substrate (the surface corresponding to the side surface of the hexagonal column when the nitride semiconductor is represented by a hexagonal column). The wafer is made into a bar shape, and a resonance surface is produced on the cleavage surface of the bar. After producing the resonance surface, a bar-shaped wafer was further cut in a direction perpendicular to the resonance surface to obtain a laser chip.

Next, when each electrode was wire-bonded and laser oscillation was attempted at room temperature, a sharp emission peak was obtained due to the effect of suppressing the occurrence of dislocations and cracks, and the threshold current density was 2.5 kA / cm ² at room temperature. Continuous oscillation with an oscillation wavelength of 375 nm was confirmed, and the lifetime was 1000 hours or longer.

  The nitride semiconductor device of the present invention can be suitably used for light emitting devices such as LEDs and LDs, and light receiving devices such as CCDs.

It is a schematic cross section showing a nitride semiconductor having an InGaN buffer layer grown on a conventional GaN-ELO substrate. It is a schematic cross-sectional view showing a nitride semiconductor in which an InGaN buffer layer is grown on a conventional free-standing GaN substrate. 1 is a schematic cross-sectional view showing a nitride semiconductor device according to an embodiment of the present invention. It is an image figure which shows the CL micrograph of the surface of the AlGaN layer grown by the structure of FIG. It is an image figure which shows CL micrograph of the surface of the AlGaN layer grown by the structure of FIG. It is an image figure which shows CL micrograph of the surface of the AlGaN layer grown by the structure of FIG. 1 is a schematic cross-sectional view showing a nitride semiconductor laser element according to Example 1 of the present invention. It is a schematic cross section showing a nitride semiconductor laser device according to Example 2 of the present invention.

DESCRIPTION OF SYMBOLS 11 ... ELO substrate 12 ... InGaN layer 13, 23 ... AlInGaN element 21, 31 ... Free-standing GaN substrate 22 ... InGaN buffer layer 32 ... First buffer layer 34 ... Second buffer layer 36 ... AlInGaN element 101, 201 ... GaN substrate 102 202, first buffer layer 103, 203 ... second buffer layer 104, 204 ... n-side cladding layer 105, 205 ... n-type light guide layer 106, 206 ... active layer 107, 207 ... p-side cap layer 108, 208 ... P-side light guide layers 109, 209... p-side cladding layers 110, 210... p-side contact layers 120, 220... p-side ohmic electrodes 121, 221. Side pad electrodes 130, 230 ... insulating film

Claims (10)

A free-standing substrate made of GaN,
A first buffer layer made of the n-Al was formed on the substrate _{x Ga 1-x N (0} <x ≦ 0.05),
A second buffer layer made of n-In _y Ga _1-y N (0 <y ≦ 0.1) formed on the first buffer layer;
An n- AlGaN layer formed on the second buffer layer;
Equipped with a,
Nitride semiconductor device which is characterized that you have contact with the first buffer layer and second buffer layer. The nitride semiconductor device according to claim 1,
A nitride semiconductor device, wherein the first buffer layer is thinner than the second buffer layer. The nitride semiconductor device according to claim 2,
The nitride semiconductor device, wherein the first buffer layer has a thickness of 300 to 3000 angstroms, and the second buffer layer has a thickness of 500 to 4000 angstroms. The nitride semiconductor device according to any one of claims 1 to 3,
The nitride semiconductor device, wherein the Si concentration of the first buffer layer is lower than the Si concentration of the second buffer layer. The nitride semiconductor device according to claim 4,
The Si concentration of the first buffer layer is 0.3 × 10 ^{18 to} 3.0 × 10 ¹⁸ cm ⁻³ , and the Si concentration of the second buffer layer is 1 × 10 ^{18 to} 5 × 10 ¹⁸ cm ^−3. A nitride semiconductor device, wherein: The nitride semiconductor device according to any one of claims 1 to 5,
A nitride semiconductor device, wherein the Al composition ratio of the AlGaN layer is 0.05 or more. The nitride semiconductor device according to any one of claims 1 to 6,
A nitride semiconductor device, wherein the substrate is a free-standing GaN substrate doped with Si or O. The nitride semiconductor device according to any one of claims 1 to 7,
The nitride semiconductor device, wherein the substrate is a substrate whose surface is processed smoothly. Gallium nitride serving as a support substrate; a first buffer layer made of n-type gallium nitride containing Al on the substrate; a second buffer layer made of n-type gallium nitride containing In on the first buffer layer; N-type gallium nitride containing Al on the second buffer layer;
Equipped with a,
Nitride semiconductor device which is characterized that you have contact with the first buffer layer and second buffer layer.   The nitride semiconductor device according to any one of claims 1 to 9,
  An active layer and a p-AlGaN layer are sequentially formed on the n-AlGaN layer or the n-type gallium nitride containing Al.