JP2008214132A - Group iii nitride semiconductor thin film, group iii nitride semiconductor light-emitting element, and method for manufacturing group iii nitride semiconductor thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-quality group III nitride semiconductor thin film; and to provide a group III nitride semiconductor light-emitting element obtained by using the same. <P>SOLUTION: A GaN-layer 120 having a (11-20) plane (so-called a-plane) is epitaxially grown on a sapphire substrate 110 having a (1-102) plane (so-called r-plane) with an off-angle of -0.1 to 0.9° against C3 crystal axis by introducing trimethyl gallium at a flow rate of 200-500 μmol/min while controlling the temperature of the sapphire substrate 110 within a range of 1,100-1,400°C. Thereby, the high-quality group III nitride semiconductor thin film (a Plane GaN layer) can be obtained. Further, The group III nitride semiconductor light-emitting element is manufactured by using the group III nitride semiconductor thin film as a substrate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a group III nitride semiconductor thin film, a group III nitride semiconductor light emitting device, and a method for manufacturing a group III nitride semiconductor thin film, and in particular, provides a (11-20) plane gallium nitride layer (a-plane GaN layer). Related to technology.

Group III nitride semiconductors, particularly gallium nitride compounds, can control the energy gap over a wide range by adjusting the mixed crystal ratio. For example, Al _x In _y Ga _1-xy N (including 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x = y = 0) behaves as a direct transition semiconductor, and its energy gap is 0.7 to It ranges from 0.8 eV to 6.2 eV. This means that by using a GaN-based compound as an active layer, a light-emitting element having all visible colors from red to ultraviolet can be realized.

  In order to apply a gallium nitride compound to such a light emitting element, it is required to provide it as a thin film with high quality and high luminous efficiency from the viewpoint of product form and life. However, gallium nitride compounds have a hexagonal Wurtzite structure, and their lattice constants are in comparison with other major semiconductors (such as III-V group compound semiconductors and II-VI group semiconductors). Shows a very small value. This extremely small lattice constant makes it difficult to match the lattice constant of the substrate crystal. In general, dislocations occur in a crystal to be epitaxially grown due to a lattice mismatch or strain (compression strain or tensile strain) with a substrate crystal. This dislocation becomes a dislocation defect and degrades the quality of the epitaxially grown film. Therefore, the selection of the substrate is important for growing the gallium nitride compound.

  Therefore, a c-plane sapphire substrate is exclusively used as a substrate for growing a GaN-based compound. Even in this sapphire substrate, the lattice constant is deviated by nearly 15% from that of GaN. Therefore, a buffer layer is actually provided between the sapphire substrate and the growth layer in order to alleviate the lattice mismatch. Up to now, the quality of the buffer layer is considered to be a factor for determining the quality of the growth layer thereon, and various buffer layers with various ideas have been proposed (see, for example, Patent Documents 1 and 2). ).

  However, even if a buffer layer is provided, when a c-plane such as sapphire is used as a crystal substrate, a GaN-based compound (hereinafter referred to as a GaN-based growth film) as a growth layer grows in the c-axis direction. In the film thickness direction, the c-axis characteristic appears remarkably. GaN-based compounds have strong piezoelectricity in the c-axis direction, and stress at the interface between compositions having different lattice constants generates a so-called polarization electric field. In an ideal active layer band without stress, the wave functions of electrons and holes exist approximately symmetrically. However, when compressive strain or tensile strain acts due to the difference in lattice constant, the distance between the wave functions of electrons and holes increases due to the presence of the polarization electric field. This means that the recombination efficiency of the active layer of the GaN-based compound grown in the c-axis direction of the substrate is lowered. On the other hand, a decrease in the distance between wave functions due to the influence of the polarization electric field leads to an increase in the emission wavelength, and causes a problem that the wavelength of the light emitting element changes depending on the degree of voltage application.

  Patent Document 3 proposes a method for growing nonpolar a-plane gallium nitride that is not affected by a polarization electric field in order to solve such a problem.

Japanese Patent Laid-Open No. 10-242586 JP-A-9-227298 US Patent Application Publication No. 2003/0198837

  However, it is not easy to grow nonpolar a-plane gallium nitride as a high-quality film because of its planar anisotropy. Specifically, in the crystal growth of gallium nitride, the Ga plane (0001) grows faster than the N plane (000-1), and this asymmetric growth causes many dislocation defects on the thin film.

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

  In order to solve the above-described problems and achieve the object, the group III nitride semiconductor thin film according to the present invention has an off angle of −0.9 ° to −0.1 ° with respect to the C3 crystal axis (1 -102) plane sapphire substrate and an epitaxially grown layer made of gallium nitride (11-20) plane located on the sapphire substrate.

  A group III nitride semiconductor light emitting device according to the present invention is characterized by including an active layer made of group III nitride formed with the above group III nitride semiconductor thin film as a base.

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

  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.

  Embodiments of a group III nitride semiconductor thin film, a method for producing the same, and a group III nitride semiconductor light emitting device according to the present invention will be described below in detail with reference to the drawings. The drawings are schematic, and the relationship between the thickness and width of each part, the size ratio between the parts, and the like are different from the actual ones. Moreover, even if it points to the same part between drawings, the dimension and ratio may mutually differ and are shown.

Embodiment 1 FIG.
First, the group III nitride semiconductor thin film according to the first embodiment and the manufacturing method thereof will be described. The group III nitride semiconductor thin film according to the first embodiment is a (1-102) plane (so-called r plane) sapphire substrate having an off angle of −0.9 ° to −0.1 ° with respect to the C3 crystal axis. (11-20) plane (so-called a plane) gallium nitride is formed thereon. Here, “−1” in (1-102) indicates that a bar is added on “1”. In this specification, the Miller index is expressed in the same way.

  FIG. 1 is a schematic cross-sectional view of a group III nitride semiconductor thin film according to the first embodiment. In FIG. 1, a group III nitride semiconductor thin film 100 includes a sapphire substrate 110 having an r-plane having an off angle of −0.9 ° to −0.1 ° with respect to the C3 crystal axis, and a sapphire substrate 110. And a non-doped a-plane GaN layer 120 formed thereon. 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 r-plane sapphire substrate 110 as shown in FIG.

  This group III nitride semiconductor thin film 100 was obtained by the following manufacturing method by the inventors' extensive research. FIG. 3 is a flowchart showing the method, that is, the a-plane GaN growth layer forming step.

  First, after preparing a sapphire substrate 110 having an r-plane having an off-angle of −0.9 ° to −0.1 ° with respect to the C3 crystal axis as a substrate surface, and cleaning the surface with an appropriate solution. And put into the reaction chamber of the MOCVD (metal organic chemical vapor deposition) apparatus. 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 at an appropriate flow rate (step S101). The r-plane 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 ° due to manufacturing errors. It is.

Next, in order to grow the a-plane GaN layer 120 on the sapphire substrate 110, hydrogen and nitrogen are introduced into the reaction chamber, and NH ₃ (ammonia) and TMGa (trimethylgallium) are introduced as source gases. did. NH ₃ was introduced after the substrate temperature was heated to 500 ° C., and TMGa was introduced after the substrate temperature was heated to 1150 ° C. The growth time of the a-plane GaN layer 120 was 50 minutes. Thereby, a good a-plane GaN thin film having a film thickness of 9.5 μm was obtained (step S102). The flow rate of TMGa was about 285 μmol / min.

  The film formation conditions of the a-plane GaN layer 120 described above are in accordance with a graph showing the relationship between the film formation rate (Growth rate) obtained by the inventors' experiment and the flow rate of TMGa. FIG. 4 is a graph of the a-plane GaN layer obtained when the flow rate of TMGa is set to 200 to 500 μmol / min when the temperature of the r-plane sapphire substrate is controlled to 1100 ° C. and 1150 ° C. Indicates thickness. In this way, good results can be obtained with a relatively high control temperature for the following reason. Usually, as the substrate temperature rises, the deposited GaN layer is etched. Specifically, the etching starts at about 900 ° C. However, the inventors have found that the etching is not severe at temperatures above about 1050 ° C. Specifically, as shown in FIG. 4, when a GaN layer is grown on a r-plane sapphire substrate at a control temperature of about 1100 ° C. and 1150 ° C. with a TMGa flow rate of 200 to 500 μmol / min, Good results were obtained. In addition, the inventors have found that the relationship between the flow rate of TMGa and the film formation rate shows similar results when the control temperature is about 1100 ° C. or higher, in addition to 1150 ° C. However, since the etching of the sapphire substrate starts when the control temperature is 1400 ° C. or higher, the optimal control temperature is substantially 1100 ° C. to 1400 ° C.

  FIG. 5 is a graph showing X-ray ω 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 dependence, but is 90 ° out of phase with the conventional a-plane GaN layer formed on the buffer layer. Further, when the off axis was measured by ω scan on the (10-12) plane, the minimum value was 1200 arcsec. This is a value considerably smaller than the off-axis (2000 arcsec) of the conventional a-plane GaN layer formed on the buffer layer. These results indicate that the a-plane GaN layer 120 obtained by the above-described film formation conditions is a high-quality thin film with few dislocations and defects.

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

In particular, the inventors have earnestly studied that a particularly good a-plane GaN thin film was obtained when NH ₃ was introduced prior to TMGa. Specifically, it was found that when NH ₃ was introduced at least 3 seconds before TMGa, a mirror surface was obtained in the a-plane GaN thin film, and surface pits appeared after that. Furthermore, the inventors have found that when the thickness of the a-plane GaN thin film is 3 μm or less, surface pits appear, and when it is more than that, a mirror surface appears. Based on this finding, the growth time was set.

Embodiment 2. FIG.
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 the second embodiment, an example in which the group III nitride semiconductor thin film according to the first embodiment is applied to an LED will be described.

  FIG. 6 is a schematic cross-sectional view of a group III nitride semiconductor light emitting device (LED) according to the second embodiment. A group III nitride semiconductor light emitting device 200 shown in FIG. 6 is based on a sapphire substrate 201 and an undoped a-plane GaN layer 202 corresponding to the sapphire substrate 110 and a-plane GaN layer 120 shown in Embodiment 1, respectively. On the a-plane GaN layer 202, an n-type contact / cladding layer 203, an active layer 204, a p-type cladding layer 205, a p-type block layer 206, and a p-type contact layer 207 are sequentially laminated.

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

  Further, the n-type contact / cladding layer 203, the active layer 204, the p-type cladding layer 205, the p-type blocking layer 206, and the p-type contact layer 207 are each exposed so that a part of the n-type contact / cladding layer 203 is exposed. A part of was removed by etching. Then, an n-type electrode 210 was provided on the exposed surface of the n-type contact / cladding layer 203. A p-type electrode 220 is provided on the p-type contact layer 207. The n-type electrode 210 is formed by depositing In, and the p-type electrode 220 is formed by depositing Ni (100Å) / Au (100Å) using an electron beam. With such a configuration, an LED was obtained.

  With respect to the obtained LED, light emission with an output wavelength of 420 nm and an output of 2 mW was observed at a drive current of 20 mA. This relatively good light emission characteristic supports the fact that the underlying a-plane GaN layer 202 is a good thin film.

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

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

1 is a side view of a group III nitride semiconductor thin film according to a first embodiment. It is a figure which defines a C3 crystal axis. It is a flowchart which shows an a surface GaN growth layer formation process. It is a graph which shows the relationship between the film-forming speed | rate of an a-plane GaN layer, and the flow volume of TMGa. 4 is a graph showing X-ray ω scan data of an a-plane GaN layer 120. FIG. 3 is a schematic cross-sectional view of a group III nitride semiconductor light emitting device according to a second embodiment.

Explanation of symbols

100 Group III nitride semiconductor thin film 110, 201 r-plane sapphire substrate 120, 202 a-plane GaN layer 200 Group III nitride semiconductor light-emitting device 203 n-type contact / cladding 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

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;
An epitaxial growth layer located on the sapphire substrate and made of (11-20) plane gallium nitride;
A group III nitride semiconductor thin film comprising:   2. The group III nitride semiconductor thin film according to claim 1, wherein the epitaxial growth layer has a thickness of 3 μm or more. A (1-102) plane sapphire substrate having an off angle of -0.9 ° to -0.1 ° with respect to the C3 crystal axis;
An epitaxial growth layer located on the sapphire substrate and made of (11-20) plane gallium nitride;
An active layer made of group III nitride formed with the epitaxial growth layer as a base;
A group III nitride semiconductor light-emitting device comprising:   4. The group III nitride semiconductor light-emitting device according to claim 3, wherein the epitaxial growth layer has a thickness of 3 μm or more. A substrate annealing step of annealing a (1-102) plane sapphire substrate having an off angle of -0.9 ° to -0.1 ° with respect to the C3 crystal axis;
By introducing trimethylgallium at a flow rate of 200 to 500 μmol / min while controlling the temperature of the sapphire substrate within a range of 1100 ° C. to 1400 ° C., (11-20) plane gallium nitride is formed on the sapphire substrate. Growing gallium nitride forming step;
A method for producing a group III nitride semiconductor thin film comprising: 6. The method for producing a group III nitride semiconductor thin film according to claim 5, wherein the gallium nitride forming step grows the gallium nitride by introducing NH ₃ before introducing the trimethyl gallium. .   7. The method for producing a group III nitride semiconductor thin film according to claim 5, wherein the gallium nitride forming step introduces the trimethyl gallium with a growth time in which the film thickness of the gallium nitride is 3 μm or more.

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