KR20080081790A - Iii-group nitrdie semiconductor thin film, iii-group nitrdie semiconductor light emitting device and fabrication method of iii-group nitrdie semiconductor thin film - Google Patents

Abstract

A III-group nitride semiconductor thin film, a III-group nitride semiconductor light emitting device, and a method of manufacturing the III-group nitride semiconductor thin film are provided to improve a light emitting speed of a blue LED by forming the LED on a desirable a-surface GaN thin film. A III-group nitride semiconductor thin film includes a sapphire substrate, an epitaxial growth layer(202), and an active layer(204). The (1-102)-surface sapphire substrate has an off-angle between -0.9 and -0.1 ° with respect to a C3 crystal axis. The epitaxial growth layer is arranged on the sapphire substrate and made of a (11-20)-surface gallium nitride. The active layer is made of a III-group nitride, which is formed by using the epitaxial growth layer as a base. A thickness of the epitaxial growth layer is greater than 3 mum. NH3 is introduced before trimethylgalium is introduced, such that the gallium nitride is grown.

Description

III-GROUP NITRDIE SEMICONDUCTOR THIN FILM, III-GROUP NITRDIE SEMICONDUCTOR LIGHT EMITTING DEVICE AND FABRICATION METHOD OF III-GROUP NITRDIE SEMICONDUCTOR THIN FILM}

1 is a side view of a group III nitride semiconductor thin film according to the first embodiment.

2 is a diagram defining a C3 crystal axis.

3 is a flow chart showing a surface GaN growth layer forming process.

4 is a graph showing the relationship between the growth rate of the a-plane GaN layer and the flow rate of TMGa.

FIG. 5 is a graph showing X-ray? Scan data of a plane GaN layer 120. FIG.

FIG. 6 is a schematic sectional view of a group III nitride semiconductor light emitting device according to Embodiment 2. FIG.

<Code Description of Main Parts of Drawing>

100 group III nitride semiconductor thin film 110, 201 r surface sapphire substrate

120, 202 a-plane GaN layer 200 III group nitride semiconductor light emitting device

203 n-type contact / clad layer 204 active layer

205 p-type cladding layer 206 p-type block layer

207 p-type contact layer 210 n-type electrode

220 p-type electrode

The present invention relates to a method for manufacturing a group III nitride semiconductor thin film, a group III nitride semiconductor light emitting device, and a group III nitride semiconductor thin film, and more particularly, to a technique for providing a (11-20) -plane gallium nitride layer (a-plane GaN layer). will be.

Group III nitride semiconductors, especially gallium nitride compounds, can control the energy gap extensively by adjusting the mixing ratio. For example, Al _x In _y Ga _1-xy N (including 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and x = y = 0) serves as a direct transition type semiconductor with an energy gap of 0.7 to It ranges from 0.8eV to 6.2eV. This means that by using a GaN compound as the active layer, it is possible to realize a light emitting device having all of the visible region from red to infrared as the emission color.

In order to apply a gallium nitride compound to such a light emitting element, it is required to provide it as a thin film of high quality and high luminous efficiency from a product form or a lifetime. However, gallium nitride-based compounds have hexagonal urtzite structure, and their lattice constants are very small compared to other major semiconductors (such as group III-V compound semiconductors and group II-VI semiconductors). Indicates. This extremely small lattice constant makes it difficult to match the lattice constant of the substrate crystal. Generally, dislocations occur in epitaxially grown crystals due to lattice mismatches and warpage (compression bending or tensile bending) with substrate crystals. This dislocation becomes a dislocation defect and degrades the quality of the epitaxial growth film. Therefore, selection of a substrate is important for growing a gallium nitride compound.

Therefore, as the substrate for growing the GaN compound, a c-plane sapphire substrate is used entirely. Even with this sapphire substrate, since the lattice constant close to 15% is GaN, the buffer layer is actually formed between the sapphire substrate and the growth layer to mitigate lattice mismatch. At present, how the quality of the buffer layer is a factor in determining the quality of the growth layer thereon, and various buffer layers inventing the invention have been proposed (for example, see Japanese Patent Application Laid-Open No. 10-242586 and See Japanese Patent Application Laid-Open No. 9-227298).

However, even when the buffer layer is formed, when the c plane such as sapphire is used as the crystal substrate, the GaN compound (hereinafter referred to as GaN-based growth film) as a growth layer grows in the c-axis direction and c in the film thickness direction. The characteristics of the axis are remarkable. GaN compounds have strong piezoelectricity in the c-axis direction, and interfacial stresses between compositions having different lattice constants generate so-called polarization electric fields. In the band of an ideal active layer without stress, the wave functions of electrons and holes are nearly symmetric. However, in the case where compressive bending or tensile bending acts due to the difference in lattice constant, the distance between the wave function of electrons and holes increases according to the presence of the polarization electric field. This means that the recombination efficiency of the active layer of the GaN compound grown in the c-axis direction of the substrate is lowered. On the other hand, the reduction in the distance between the wave functions due to the influence of the polarization electric field causes the long wavelength of the light emission wavelength, and also causes the problem that the growth of the light emitting element changes depending on the degree of voltage application.

US Patent Application Publication No. 2003/0198837 discloses a method of growing nonpolar gallium nitride, which is not affected by polarization fields, to solve this problem.

However, because of its planar anisotropy, nonpolar gallium nitride is not easy to grow as a good quality film. Specifically, in the crystal growth of gallium nitride, the Ga surface (0001) grows faster than the N surface (000-1), and many dislocation defects occur in the thin film phase due to this asymmetrical growth.

Therefore, formation of a high quality GaN-based growth film using nonpolar a-plane gallium nitride is expected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to provide a high quality group III nitride semiconductor thin film using nonpolar a-plane gallium nitride.

Another object of the present invention is to provide a group III nitride semiconductor light emitting device using the nitride thin film.

It is still another object of the present invention to provide a method for producing the above-mentioned group III nitride semiconductor thin film.

In order to achieve the above technical problem, the group III nitride semiconductor thin film according to an aspect of the present invention, the (1-102) surface sapphire substrate having an off angle of -0.9 ° to -0.1 ° with respect to the C3 crystal axis, It is located on the sapphire substrate and comprises an epitaxial growth layer made of gallium nitride on the (11-20) plane.

In addition, the Group III nitride semiconductor light emitting device according to another aspect of the present invention comprises an active layer made of Group III nitride formed based on the Group III nitride semiconductor thin film.

Furthermore, in the method of manufacturing a group III nitride semiconductor thin film according to another aspect of the present invention, the substrate annealing step of annealing a (1-102) surface sapphire substrate having an off angle of -0.9 ° to -0.1 ° with respect to the C3 crystal axis. Nitriding the gallium nitride on the (11-20) plane on the sapphire substrate by introducing trimethylgallium at a flow rate of 200 to 500 µmol / min while controlling the temperature of the sapphire substrate within the range of 1100 ° C to 1400 ° C. Gallium forming step.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of group III nitride semiconductor thin film which concerns on this invention, its manufacturing method, and group III nitride semiconductor light emitting element is described in detail based on drawing.

In addition, the figure is typical, and the relationship of the thickness and width of each part, the size ratio between parts, etc. differs from an actual thing. In addition, even if the same part is shown between drawings, the magnitude | size and the ratio may mutually differ.

First embodiment

First, the group III nitride semiconductor thin film according to the first embodiment and a manufacturing method thereof will be described. The group III nitride semiconductor thin film according to the first embodiment has the (11-20) plane (on the (1--20) plane (so-called r plane) having an off angle of -0.9 ° to -0.1 ° with respect to the C3 crystal axis. So-called gallium nitride of a side) is formed. Here, '-1' in (1-102) indicates that a bar is attached on '1'. In the present specification, the mirror index is equally represented.

1 is a schematic cross-sectional view of a group III nitride semiconductor thin film according to the first embodiment. In FIG. 1, the group III nitride semiconductor thin film 100 is formed on the sapphire substrate 110 and the sapphire substrate 110 having the r surface as the substrate surface having an off angle of -0.9 ° to -0.1 ° with respect to the C3 crystal axis. It is composed of a non-doped a-side GaN layer 120. Here, the C3 crystal axis is defined as an axis passing through the center of the sapphire substrate 110 in the a-axis direction of the sapphire substrate 110 on the r surface.

This group III nitride semiconductor thin film 100 is obtained by the following manufacturing method based on the research of the inventors' experimental example. 3 is a flowchart showing the method, that is, the a-plane GaN growth layer forming process.

First, a sapphire substrate 110 whose r surface has an off angle of -0.9 ° to -0.1 ° with respect to the C3 crystal axis is prepared, and the surface is washed with a suitable solution, followed by MOCVD (organic metal). Chemical vapor growth). As a pre-process in the reaction chamber, the substrate temperature was controlled to 1150 ° C., and annealing was performed for about 10 minutes in a hydrogen atmosphere of a suitable flow rate (step S101). In addition, this r surface sapphire substrate 110 is actually a substrate surface having an off angle of -0.5 ° with respect to the C3 crystal axis, and is expected to be ± 0.4 ° C due to manufacturing error.

Subsequently, in order to grow the a-plane GaN layer 120 on the sapphire substrate 110, hydrogen and nitrogen were introduced into the reaction chamber as a carrier gas, and NH ₃ (ammonia) and TMGa (trimethylgallium) were used as source gases. Introduced. NH ₃ started introduction after heating the substrate temperature to 500 ° C., and TMGa started introduction after heating the substrate temperature to 1150 ° C. The growth time of the a-plane GaN layer 120 was 50 minutes. As a result, a good a-plane GaN thin film having a thin film of 9.5 mu m was obtained (step S102). The flow rate of TMGa was about 285 μmol / min.

The deposition conditions of the a-plane GaN layer 120 described above are in accordance with a graph showing the relationship between the growth rate obtained by the inventors' experiment and the flow rate of TMGa. Fig. 4 is a graph showing the film thickness of the a-plane GaN layer obtained when the flow rate of TMGa is set to 200 to 500 µmol / min when the sapphire substrate temperature of the r-plane is controlled to 1100 ° C and 1150 ° C. . This relatively high control temperature and good results are obtained for the following reasons.

Usually, the GaN layer grown with the increase of substrate temperature is etched. Specifically, the etching starts at about 900 ° C. However, the inventors found that the degree of etching was not severe above about 1050 ° C. Specifically, as shown in FIG. 4, when the GaN layer was grown at a flow rate of 200-500 µmol / min TMGa together at a control temperature of about 1100 ° C. and 1150 ° C. on the r surface sapphire substrate, good results were obtained. In addition, the inventors have found that the relationship between the flow rate and the growth rate of the TMGa is the same as the control temperature of about 1100 ° C or more in addition to 1150 ° C. However, since the etching of a sapphire substrate starts when control temperature becomes 1400 degreeC or more, substantially 1100 degreeC-1400 degreeC will become an optimal control temperature.

Fig. 5 is a graph showing X-ray? Scan data of the a-plane GaN layer 120 obtained by the above method. As shown in FIG. 5, the a-plane GaN layer 120 exhibits φ angle requestability, but the phase is 90 ° off compared with the conventional a-plane GaN layer formed on the buffer layer. Further, the off axis was measured by ω scan on the (10-12) plane, and the minimum value was 1200 arcsec. This is considerably smaller than the off layer (2000 arcsec) of the conventional a-plane GaN layer formed on the buffer layer. These results show that the a-plane GaN layer 120 obtained according to the film forming conditions described above is a high quality thin film with few dislocations and defects.

As described above, trimethylgallium is 200 while preparing a sapphire substrate with an r surface having a -0.9 ° to -0.1 ° off angle with respect to the C3 crystal axis, and controlling the temperature of the substrate within the range of 1100 ° C to 1400 ° C. By introducing at a flow rate of ˜500 μmol / min, a high quality gallium nitride thin film can be grown on the sapphire substrate on the r surface.

In particular, it is in accordance with an example of the inventors that a particularly good a-plane GaN thin film is obtained when NH ₃ is introduced before TMGa. Specifically, it was found that when NH ₃ was introduced three seconds or more before TMGa, a mirror surface was obtained from the a-plane GaN thin film, and surface pits appeared later than that. In addition, the inventors found that surface pits appeared when the film thickness of the a-plane GaN thin film was 3 µm or less, and mirror surfaces appeared when the a-side GaN thin film was made larger. Based on this, the growth time was set.

2nd Embodiment

The group III nitride semiconductor thin film according to the first embodiment described above can be used as a base layer constituting a group III nitride semiconductor light emitting device such as an LED or a semiconductor laser. In Embodiment 2, an example in which a group III nitride semiconductor thin film according to Embodiment 1 is applied to an LED will be described.

6 is a schematic cross-sectional view of a group III nitride semiconductor light emitting element (LED) according to the second embodiment. The group III nitride semiconductor light emitting device 200 shown in FIG. 6 includes a sapphire substrate 201 and an undoped a-plane GaN layer 202 corresponding to the sapphire substrate 110 and the a-plane GaN layer 202 shown in the first embodiment, respectively. ), The n-type contact / clad layer 203, the active layer 204, the p-type cladding layer 205, the p-type block layer 206, and the p-type contact on the a-plane GaN layer 202. The layer 207 has a stacked structure in order.

The inventors obtained a sample of the group III nitride semiconductor light emitting device 200 under the following conditions. First, an n-type contact / cladding layer 203 was grown on a surface GaN layer 202 obtained according to the method described in Embodiment 1 at a control temperature of 1150 ° C as Si was doped with GaN. Subsequently, Ga and In as source gases were introduced on the n-type contact / clad layer 203 at an appropriate flow rate at a control temperature of 730 ° C., whereby an active layer 204 made of InGaN was grown. Subsequently, the p-type cladding layer 205 was grown at a control temperature of 1000 ° C. by doping Mg to GaN. Subsequently, the p-type block layer 206 was grown at a control temperature of 1150 ° C by injecting Mg into AlGaN. Then, the p-type contact layer 207 was grown at a control temperature of 1000 DEG C by doping Mg into GaN.

In addition, the n-type contact / cladding layer 203, the active layer 204, the p-type cladding layer 205, the p-type block layer 206, and the p-type contact layer 207 are n-type contact / cladding layers 203. Each part was removed by etching so that a part of the was exposed. Then, the n-type electrode 210 was provided on the exposed n-type contact / clad layer 203. The p-type electrode 220 was provided on the p-type contact layer 207. The n-type electrode 210 is formed by tracking In and the p-type electrode 220 using Ni (100 kV) / Au (100 kV), respectively, using an electron beam. According to such a configuration, an LED was obtained.

With respect to the obtained LED, light emission with an output of 2 GHz with a light emission wavelength of 420 nm was observed with a driving current of 20 mA. This relatively good luminescence property supports that the base a-plane GaN layer 202 is a good thin film.

As described above, according to the second embodiment, by forming an LED on a high quality a-plane GaN thin film, a blue light emitting device with high reliability and sufficient light emission rate can be provided.

As described above, the group III nitride semiconductor thin film according to the present invention is useful as a base layer for forming a GaN compound, and is particularly suitable as a component of a group III nitride semiconductor light emitting device.

As described above, according to the present invention, it is possible to provide a group III nitride semiconductor thin film including a high quality a-plane gallium nitride thin film and a group III nitride semiconductor light emitting device using the same as a base.

Claims (7)

A (1-102) plane sapphire substrate having an off angle of -0.9 ° to -0.1 ° with respect to the C3 crystal axis; And A III-nitride semiconductor thin film, comprising: an epitaxial growth layer on the sapphire substrate, the epitaxial growth layer consisting of gallium nitride (11-20). The method of claim 1, A group III nitride semiconductor thin film, wherein the epitaxially grown layer has a thickness of 3 µm or more. (1-102) sapphire substrate having an off angle of -0.9 ° to -0.1 ° with respect to the C3 crystal axis; An epitaxial growth layer on the sapphire substrate, the epitaxial growth layer comprising gallium nitride on a (11-20) plane; And Group III nitride semiconductor light emitting device comprising a; an active layer made of a group III nitride formed based on the epitaxial growth layer. The method of claim 3, The III-nitride semiconductor light emitting device according to claim 1, wherein the epitaxial growth layer has a thickness of 3 µm or more. A substrate annealing step of annealing the (1-102) faceted sapphire substrate having an off angle of -0.9 ° to -0.1 ° with respect to the C3 crystal axis; And Gallium nitride for growing (11-20) plane gallium nitride on the sapphire substrate by introducing trimethylgallium at a flow rate of 200 to 500 µmol / min while controlling the temperature of the sapphire substrate in the range of 1100 ° C to 1400 ° C. Forming step; method of manufacturing a III-nitride semiconductor thin film comprising a. The method of claim 5, The gallium nitride forming step is a group III nitride semiconductor thin film, characterized in that for growing the gallium nitride by introducing NH ₃ before the introduction of the trimethylgallium. The method according to claim 5 or 6, In the gallium nitride forming step, the trimethylgallium is introduced at a growth time such that the gallium nitride has a thickness of 3 μm or more.

Images