JP5375392B2 - Gallium nitride based semiconductor optical device and method for fabricating gallium nitride based semiconductor optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN-based semiconductor optical device capable of preventing the deterioration of light emission characteristics caused by indium segregation in an active layer. <P>SOLUTION: In the GaN-based semiconductor optical device 11a, the principal plane 13a of a template 13 tilts from a surface perpendicular to a reference axis Cx that extends along the c-axis of this first GaN-based semiconductor in the direction of the m-axis of the first GaN-based semiconductor with the tilt angle in the range of &ge;63 degrees and less than 80 degrees. A GaN-based based semiconductor epitaxial region 15 is formed on the principal plane 13a. An active layer 17 is formed on the GaN-based based semiconductor epitaxial region 15. The active layer 17 includes at least one semiconductor epitaxial layer 19 composed of InGaN. The direction of the film thickness of the semiconductor epitaxial layer 19 tilts toward the reference axis Cx. This reference axis Cx is directed toward the direction of the axis [0001] of the first GaN-based semiconductor. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a GaN-based semiconductor optical device and a method for manufacturing a GaN-based semiconductor optical device.

  Patent Document 1 describes a method for manufacturing a group III-V nitride semiconductor free-standing substrate. According to this method, a group III-V nitride semiconductor free-standing substrate having a predetermined off angle suitable for epitaxial growth of a group III-V nitride semiconductor can be manufactured. After growing an epitaxial layer of a group III-V nitride semiconductor single crystal on a sapphire substrate having a surface inclined at an angle of 0.07 to 20 degrees in the a-axis direction or the m-axis direction from the c-plane, the epitaxial layer Is peeled from the dissimilar substrate.

  Patent Document 2 describes a nitride semiconductor light-emitting element composed of a gallium nitride-based semiconductor layer formed on a heterogeneous substrate. It is formed on the substrate via a buffer layer. Etch processing is performed on the n-type semiconductor layer to form a surface having a plane orientation different from the C plane. An active layer is grown by bonding to the A plane and the C plane. When an active layer in contact with two kinds of plane orientations is formed, the thickness of the quantum well width (active layer) differs from each other due to the difference in growth rate. Therefore, a plurality of colors can be obtained with different emission wavelength peaks.

  In Patent Document 3, after a nitride semiconductor is grown on a different substrate made of a material different from that of the nitride semiconductor, a concave portion is partially formed in the nitride semiconductor. After exposing the surface on which the lateral growth of the nitride semiconductor can be performed on the side surface of the recess, another nitride semiconductor is grown on the nitride semiconductor. An n-type nitride semiconductor, an active layer, and a p-type nitride semiconductor are grown on the other nitride semiconductor.

  Non-Patent Documents 1 and 2 describe the calculation of the piezoelectric field.

JP 2005-343713 A JP 2005-129905 A Japanese Patent Laid-Open No. 2005-20034

Japanese Journal of Applied Physics vol.39 (2000) pp.413 Journal of Applied Physics vol.91 No.12 (2002) pp.9904

  According to the knowledge of the inventors, when a light emitting element having a long wavelength is produced on a substrate different from the method of the above-mentioned patent document, for example, a self-standing GaN substrate, the plane orientation of the surface of the GaN substrate can be adjusted. At present, the cost of the free-standing GaN substrate is high, and it is not easy to increase the size of the free-standing GaN substrate. Furthermore, a great deal of technological development is required to obtain a practically sized free-standing GaN substrate having a desired plane orientation.

  A crystal plane inclined at an angle of about 5 degrees to 20 degrees from the c-plane as in Patent Document 1 does not exhibit desired indium uptake performance. Therefore, it is necessary to lower the growth temperature of the InGaN layer in order to obtain an indium composition that can provide long-wavelength light emission. Lowering the growth temperature makes it difficult to improve the quality of the InGaN layer.

  On a nonpolar surface such as a-plane as in Patent Document 2, the step density on the growth surface is small and the terrace is large. Although the indium uptake performance in this plane orientation is excellent, In segregation is likely to occur, and the possibility of In segregation increases with a large indium composition.

  On the other hand, the light emission of the GaN-based semiconductor optical device can be changed in a wide wavelength range. As the light emitting layer, a GaN-based semiconductor layer containing indium can be used. The emission wavelength is changed by adjusting the indium composition in the light emitting layer. One example of this GaN-based semiconductor layer is InGaN. InGaN exhibits strong immiscibility. For this reason, in the InGaN growth, the In composition fluctuates spontaneously, and In segregates. In segregation is observed not only in InGaN but also in other indium-containing GaN-based semiconductors. Further, In segregation is remarkable when the In composition is increased due to the change of the emission wavelength.

  The segregation of In in the light emitting layer increases the threshold current in a semiconductor laser, for example. In addition, segregation of In in the light emitting layer causes uneven surface emission in, for example, a light emitting diode. Therefore, it is desirable to reduce In segregation in any light emitting element.

  The inventors are examining the production of InGaN-based light-emitting elements on different substrates. In order to obtain a desired InGaN well layer in c-plane GaN on a heterogeneous substrate, the indium composition of the well layer is adjusted. The crystal quality of the InGaN layer decreases with an increase in In composition, resulting in a decrease in emission intensity and an increase in emission spectrum half width.

  The present invention has been made in view of the above circumstances, and is a gallium nitride semiconductor light-emitting element that is provided on a heterogeneous substrate made of a material different from that of a gallium nitride semiconductor and can suppress a decrease in light emission characteristics due to In segregation. An object of the present invention is to provide a method for manufacturing this gallium nitride based semiconductor light emitting device.

  A gallium nitride based semiconductor optical device according to one aspect of the present invention includes (a) a support having a main surface made of a material different from that of a gallium nitride based semiconductor, a mask having an opening and covering the main surface, A recess provided on the main surface in the opening and having first and second side surfaces, an insulator covering the second side surface, and a semiconductor provided on the first and second side surfaces and embedding the mask A template including a region, (b) a gallium nitride based semiconductor epitaxial region provided on the template, and (c) a semiconductor epitaxial layer provided on the gallium nitride based semiconductor epitaxial region for an active layer. Prepare. The semiconductor region is made of a first gallium nitride semiconductor, the c-axis direction of the first gallium nitride semiconductor is defined by the orientation of the first side surface, and the main surface of the semiconductor region of the template is The first gallium nitride semiconductor is inclined at an inclination angle ranging from 63 degrees to less than 80 degrees in the direction of the m axis of the first gallium nitride semiconductor from a plane orthogonal to the reference axis extending along the c axis. The first side surface is inclined with respect to the main surface of the support, and an intersection angle between the main surface of the support and the first side surface is 63 degrees or more and less than 80 degrees. The second side surface is inclined with respect to the main surface of the support, and the semiconductor epitaxial layer is made of a second gallium nitride-based semiconductor containing indium as a constituent element, Second gallium nitride semiconductor The axis is inclined with respect to the normal axis of the main surface of the semiconductor region, and the direction of the reference axis is either the [0001] axis or the [000-1] axis of the first gallium nitride semiconductor. Direction.

  According to this gallium nitride based semiconductor optical device, the main surface of the support is inclined at an inclination angle in the range of not less than 63 degrees and less than 80 degrees with respect to the first side surface, and the insulator covers the second side surface. When the semiconductor region is provided on the support so as to embed the insulating film on the second side surface, the first side surface, and the mask, the main surface of the semiconductor region also extends along the c-axis of the first gallium nitride semiconductor. The first gallium nitride semiconductor is inclined at an inclination angle ranging from 63 degrees to less than 80 degrees in the direction of the m-axis of the first gallium nitride semiconductor from a plane orthogonal to the extending reference axis. In the template having the above inclination angle, the morphology of the main surface of the semiconductor region is also composed of a plurality of narrow terraces. Also, since the GaN-based semiconductor epitaxial region is provided on the template, the GaN-based semiconductor epitaxial region takes over the crystal axis of the template semiconductor region. Therefore, the GaN-based semiconductor epitaxial region extends along a plane inclined at an angle in the range of 63 degrees or more and less than 80 degrees in the m-axis direction from a plane orthogonal to the reference axis extending along the c-axis. Therefore, the morphology of the main surface of the GaN-based semiconductor epitaxial region also has a plurality of terraces with a narrow width. This terrace arrangement constitutes a microstep. Since the terrace width is narrow in the above angle range, nonuniformity of the In composition is unlikely to occur over a plurality of terraces. Therefore, a decrease in light emission characteristics due to In segregation is suppressed. Further, since the terrace structure is defined by an inclination angle from the c-axis, a template in which the inclination angle is defined with reference to the {0001} plane of the first GaN-based semiconductor, and the inclination angle is the first GaN-based In any of the templates that are defined based on the {000-1} plane of the semiconductor, the deterioration of the light emission characteristics is suppressed. In other words, even if the reference axis is oriented in either the [0001] axis or the [000-1] axis of the first GaN-based semiconductor, a decrease in light emission characteristics is suppressed.

  In the gallium nitride based semiconductor optical device according to the present invention, the main surface of the semiconductor region is inclined at an angle of 70 degrees or more from the plane perpendicular to the reference axis in the m-axis direction of the first gallium nitride based semiconductor. It is preferable. In this GaN-based semiconductor optical device, the substrate main surface in this angular range has a plurality of terraces that are narrower. Therefore, In segregation is reduced.

  In the gallium nitride based semiconductor optical device according to the present invention, the main surface of the semiconductor region is 71 degrees or greater and 79 degrees or less from a plane perpendicular to the reference axis in the m-axis direction of the first gallium nitride based semiconductor. It is preferable to be inclined at an angle. According to this GaN-based semiconductor optical device, the balance between step end growth and growth on the terrace is good. Therefore, In segregation is reduced.

  In the gallium nitride based semiconductor optical device according to the present invention, the off angle in the a-axis direction of the first gallium nitride based semiconductor may be a finite value, and may be in the range of −3 degrees to +3 degrees. According to this GaN-based semiconductor optical device, the off angle in the a-axis direction improves the surface morphology of the epitaxial region and reduces In segregation.

  The gallium nitride based semiconductor optical device according to the present invention may include a second conductivity type gallium nitride based semiconductor layer provided on the active layer. The gallium nitride based semiconductor epitaxial region includes a first conductivity type gallium nitride based semiconductor layer, the active layer includes well layers and barrier layers alternately arranged in a predetermined axis direction, and the well layer includes the well layer The barrier layer is made of a gallium nitride based semiconductor, the semiconductor epitaxial layer is made of InGaN containing a strain, the first conductivity type gallium nitride based semiconductor layer, the active layer, and the second layer The conductive gallium-based semiconductor layers are arranged in the direction of the predetermined axis, and the direction of the reference axis is different from the direction of the predetermined axis.

  According to this GaN-based semiconductor optical device, small In segregation is achieved not only in a semiconductor epitaxial layer composed of a single layer film but also in an active layer having a quantum well structure.

  In the gallium nitride based semiconductor optical device according to the present invention, the active layer is preferably provided so as to generate an emission wavelength of 370 nm or more. According to this GaN-based semiconductor optical device, In segregation can be reduced in the range of the indium composition that achieves an active layer that generates an emission wavelength of 370 nm or more. Moreover, it is preferable that the said active layer is provided so that the light emission wavelength which is 650 nm or less may be produced | generated. According to this GaN-based semiconductor optical device, in the active layer that generates an emission wavelength of 650 nm or more, the semiconductor epitaxial layer has a large indium composition, so that it is difficult to obtain a semiconductor epitaxial layer having a desired crystal quality.

  In the gallium nitride based semiconductor optical device according to the present invention, the active layer is preferably provided so as to generate an emission wavelength of 480 nm or more. In the GaN-based semiconductor optical device according to the present invention, the active layer is preferably provided so as to generate an emission wavelength of 600 nm or less. According to this GaN-based semiconductor optical device, In segregation is reduced. An inclination angle in the range of 63 degrees to less than 80 degrees is effective in the emission wavelength range of 480 nm to 600 nm.

  In the gallium nitride based semiconductor optical device according to the present invention, the main surface of the semiconductor region is from either the {20-21} plane or the {20-2-1} plane of the first gallium nitride based semiconductor. The semiconductor surface may be inclined at an angle in a range of 3 degrees to 3 degrees. According to this gallium nitride based semiconductor optical device, the {20-21} plane and the {20-2-1} plane are inclined at about 75 degrees from the plane orthogonal to the reference axis. Good light emission characteristics are shown in the vicinity of this angle. In the gallium nitride based semiconductor optical device according to the present invention, the main surface of the semiconductor region is either the {20-21} plane or the {20-2-1} plane of the first gallium nitride based semiconductor. It can be a semiconductor surface. In these plane orientations, In segregation is reduced.

  In the gallium nitride based semiconductor optical device according to the present invention, the reference axis is in the direction of the [0001] axis. Alternatively, in the gallium nitride based semiconductor optical device according to the present invention, the reference axis is in the direction of the [000-1] axis.

In the gallium nitride based semiconductor optical device according to the present invention, the semiconductor layer of the template is made of In _S Al _T Ga _1- STN (0 ≦ S ≦ 1, 0 ≦ T ≦ 1, 0 ≦ S + T <1). Can be. In the gallium nitride based semiconductor optical device according to the present invention, the semiconductor layer of the template is preferably made of GaN. According to this gallium nitride based semiconductor optical device, since GaN is a GaN based semiconductor that is a binary compound, good crystal quality and a stable semiconductor main surface are provided.

  In the gallium nitride based semiconductor optical device according to the present invention, the surface morphology of the main surface of the substrate has a plurality of microsteps. The main constituent surfaces of the microstep include at least an m-plane and a {10-11} plane. In this GaN-based semiconductor optical device, the incorporation of In is good at the above-described configuration surface and step end. In addition, In segregation is reduced.

  In the gallium nitride based semiconductor optical device according to the present invention, the support may be made of any one of spinel, sapphire, zinc oxide, silicon carbide, silicon and gallium oxide. According to this gallium nitride based semiconductor optical device, these materials can provide the template with the semiconductor region of the main surface inclined at an inclination angle in the range of 63 degrees or more and less than 80 degrees.

  In the gallium nitride based semiconductor optical device according to the present invention, the semiconductor region is an epitaxial film grown epitaxially in the c-axis direction of the first gallium nitride based semiconductor on the first side surface of the recess. According to this gallium nitride based semiconductor optical device, the plane orientation is defined on the main surface of the semiconductor region by the angle formed by the first side surface of the support and the main surface of the support.

  Another aspect of the present invention is a method for fabricating a gallium nitride based semiconductor optical device. This method includes (a) a support having a main surface made of a material different from that of a gallium nitride based semiconductor, a mask having an opening and covering the main surface, and a first surface provided on the main surface in the opening of the mask. And providing a template including a recess having a second side surface, an insulator covering the second side surface, and a semiconductor region provided on the first and second side surfaces and embedding the mask; (B) growing a gallium nitride based semiconductor epitaxial region on the main surface; and (c) forming a semiconductor epitaxial layer for an active layer on the main surface of the gallium nitride based semiconductor epitaxial region. Is provided. The semiconductor region is made of a first gallium nitride-based semiconductor, and the main surface of the template semiconductor region is formed from a surface orthogonal to a reference axis extending along the c-axis of the first gallium nitride-based semiconductor. The gallium nitride semiconductor 1 is inclined at an inclination angle in a range of 63 degrees or more and less than 80 degrees in the m-axis direction, and an intersection angle between the main surface of the support and the first side surface is 63 degrees or more and 80 degrees. The first side surface is inclined with respect to the main surface of the support body, and the second side surface is inclined with respect to the main surface of the support body. The semiconductor epitaxial layer is made of a second gallium nitride semiconductor containing indium as a constituent element, and the c-axis of the second gallium nitride semiconductor is inclined with respect to the normal axis of the main surface of the semiconductor region. The semiconductor epitaxy The layer is made of a second gallium nitride based semiconductor, the second gallium nitride based semiconductor contains indium as a constituent element, and the c-axis of the second gallium nitride based semiconductor is inclined with respect to the reference axis. The reference axis is directed to either the [0001] axis or the [000-1] axis of the first gallium nitride semiconductor.

  According to this method, the main surface of the support body is inclined with respect to the first side surface in the m-axis direction at an inclination angle in the range of not less than 63 degrees and less than 80 degrees, and the insulator covers the second side surface. A semiconductor region is grown on the support to embed the insulating film on the second side, the first side, and the mask. Therefore, the main surface of the semiconductor region is also 63 degrees or more in the direction of the m-axis of the first gallium nitride semiconductor from the plane orthogonal to the reference axis extending along the c-axis of the first gallium nitride semiconductor. Tilt at an inclination angle in the range of less than 80 degrees. When the main surface of the semiconductor region forms the above-described inclination angle, the main surface of the semiconductor region is composed of a plurality of narrow terraces. Further, since the gallium nitride based semiconductor epitaxial region is provided on the main surface of the semiconductor region, the crystal axis of the gallium nitride based semiconductor epitaxial region takes over the crystal axis of the semiconductor region. Therefore, the main surface of the gallium nitride based semiconductor epitaxial region is also inclined at an angle in the range of 63 degrees to less than 80 degrees in the m-axis direction from the reference axis extending along the c-axis. Accordingly, the main surface of the gallium nitride based semiconductor epitaxial region also has a plurality of narrow terraces. A microstep is constituted by the arrangement of these terraces. In the above angle range, the terrace is narrow. Because of the narrow terrace width, the migration of In atoms attached to each terrace is hindered. Therefore, nonuniformity of the In composition hardly occurs over a plurality of terraces. Therefore, a decrease in light emission characteristics due to In segregation is suppressed. Further, since the terrace structure is defined by the inclination angle from the c-axis, the template defined on the basis of the {0001} plane of the first GaN-based semiconductor and the {000-1} plane of the first GaN-based semiconductor In any of the templates stipulated in the reference, the deterioration of the light emission characteristics is suppressed. That is, when the direction of the reference axis is one of the [0001] axis and the [000-1] axis of the first gallium nitride semiconductor, a decrease in light emission characteristics is suppressed.

  In the method according to the present invention, the main surface of the semiconductor region is inclined at an angle in a range of 70 degrees or more from a plane orthogonal to the reference axis in the m-axis direction of the first gallium nitride semiconductor. It is preferable. In this method, the template main surface in this angular range has a plurality of terraces that are narrower. In the method according to the present invention, the main surface of the semiconductor region is inclined at an angle of 71 degrees or more and 79 degrees or less from a plane orthogonal to the reference axis in the m-axis direction of the first gallium nitride semiconductor. Preferably it is. According to this gallium nitride based semiconductor optical device, the step edge growth and the growth on the terrace are well balanced.

  In the method according to the present invention, the active layer has a quantum well structure including well layers and barrier layers alternately arranged in a predetermined axis direction, and the semiconductor epitaxial layer is the well layer, The barrier layer is preferably made of a gallium nitride based semiconductor. The method may further include a step of forming the barrier layer on the semiconductor epitaxial layer and a step of growing a second conductivity type gallium nitride based semiconductor layer on the active layer. The gallium nitride based semiconductor epitaxial region includes a first conductivity type gallium nitride based semiconductor layer, and the first conductivity type gallium nitride based semiconductor layer, the active layer, and the second conductivity type gallium nitride based semiconductor layer are predetermined Arranged in the direction of the axis, the direction of the reference axis is different from the direction of the predetermined axis.

  In this method, small In segregation is achieved not only in the growth of a semiconductor epitaxial layer composed of a single layer film but also in the growth of an active layer having a quantum well structure.

  In the method according to the present invention, the off-angle in the a-axis direction of the first gallium nitride semiconductor is preferably a finite value, and is preferably in the range of −3 degrees to +3 degrees. According to this method, an epitaxial region having a good surface morphology can be grown by an off angle from the a-axis direction.

  In the method according to the present invention, the inclination angle of the main surface of the semiconductor region is the crystal plane of either the {20-21} plane or the {20-2-1} plane of the first gallium nitride semiconductor. From −3 degrees to +3 degrees. According to this method, the {20-21} plane and the {20-2-1} plane are inclined at 75.09 degrees from the reference axis. Good light emission characteristics are shown in the vicinity of this angle.

In the method according to the present invention, the semiconductor region may be made of In _S Al _T Ga _1- STN (0 ≦ S ≦ 1, 0 ≦ T ≦ 1, 0 ≦ S + T <1). In the method according to the present invention, the semiconductor region is preferably made of GaN. According to this method, since GaN is a GaN-based semiconductor that is a binary compound, good crystal quality and a stable semiconductor main surface are provided.

  In the method according to the present invention, the surface morphology of the main surface of the semiconductor region has a plurality of microsteps, and main constituent surfaces of the microstep include at least an m-plane and a {10-11} plane. . In this method, the incorporation of In is good at the above-described configuration surface and step end. For this reason, the segregation of In is reduced.

  In the method according to the present invention, the support may be composed of any one of spinel, sapphire, zinc oxide, silicon carbide, silicon, and gallium oxide. According to this method, these materials can provide the template with a semiconductor region of the main surface inclined at an inclination angle in the range of 63 degrees or more and less than 80 degrees.

  In the method according to the present invention, the semiconductor region is epitaxially grown in the c-axis direction of the first gallium nitride based semiconductor selectively on the first side surface of the recess with respect to the second side surface. Semiconductors can be included. According to this method, the plane orientation can be defined on the main surface of the semiconductor region by the intersection angle between the first side surface of the support and the main surface of the support.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, a gallium nitride-based semiconductor light-emitting element that is provided on a different substrate made of a material different from that of a gallium nitride-based semiconductor and can suppress a decrease in light emission characteristics due to In segregation is provided. Further, according to the present invention, a method for producing this gallium nitride based semiconductor light emitting device is provided.

FIG. 1 is a drawing schematically showing the structure of a GaN-based semiconductor optical device according to the present embodiment. FIG. 2 is a drawing schematically showing the structure of the GaN-based semiconductor optical device according to the present embodiment. FIG. 3 is a diagram showing a template structure in the GaN-based semiconductor optical device shown in FIGS. 1 and 2. FIG. 4 is a drawing showing a process flow including main processes in the production of a template. FIG. 5 is a drawing schematically showing main steps in the production of a template. FIG. 6 is a drawing schematically showing main steps in the production of a template. FIG. 7 is a drawing schematically showing the inclination angle of the main surface of the dissimilar substrate for obtaining a template having a desired inclination angle. FIG. 8 is a view showing epitaxial substrates E1 and E2 according to the first embodiment. FIG. 9 is a drawing showing the results of X-ray diffraction and theoretical calculations. FIG. 10 is a drawing showing the main steps of a method for producing a GaN-based semiconductor optical device according to this embodiment. FIG. 11 is a view showing a light emitting diode structure (LED1, LED2) according to Example 2. FIG. 12 is a diagram showing electroluminescence spectra of the light emitting diode structures LED1 and LED2. FIG. 13 is a drawing showing cathodoluminescence (CL) images on the epitaxial substrates E3 and E4. FIG. 14 is a drawing showing the measurement of the relationship between the emission wavelength and the current injection amount in the light emitting diode structures LED1 and LED2. FIG. 15 is a diagram showing calculation results regarding the piezoelectric field. FIG. 16 is a diagram showing electroluminescence of a well layer light emitting diode structure having different In compositions. FIG. 17 is a diagram showing the external quantum efficiency and human visibility curve of an InGaN well layer light emitting diode and an AlGaInP well layer. 18 is a drawing showing a laser diode structure (LD1) according to Example 4. FIG. FIG. 19 is a drawing showing the relationship between the In composition and the off angle of InGaN deposited on a GaN main surface having various inclination angles (off angles) taken from the c axis in the m-axis direction. FIG. 20 is a drawing schematically showing the deposition of an In-containing GaN-based semiconductor on a GaN-based semiconductor surface having a c-plane and an off angle β. FIG. 21 is a drawing schematically showing a semiconductor laser in Example 6. FIG. 22 is a drawing showing a photoluminescence (PL) spectrum PL + 75 of a quantum well structure on an m-plane + 75 ° off-GaN substrate and a PL spectrum PL-75 of a quantum well structure on an m-plane + 75 ° off-GaN substrate. FIG. 23 is a drawing schematically showing a growth mode when the growth temperature is high and a growth mode when the growth temperature is low. FIG. 24 is a drawing showing an AFM image of a growth surface of GaN grown by step flow growth and growth on a terrace. FIG. 25 schematically shows the growth mechanism of step-flow growth in the high-temperature growth of GaN and InGaN on the non-stable surface, and the growth mechanism of growth on the terrace and step edge growth in the low-temperature growth of GaN and InGaN on the non-stable surface. It is a drawing. FIG. 26 is a diagram showing experimental results of growing InGaN under the same conditions at 760 degrees Celsius on a GaN substrate inclined at various inclination angles in the m-axis direction from the c-plane. FIG. 27 is a drawing showing a surface atomic arrangement of {10-11} plane as an example. FIG. 28 is a drawing showing an atomic arrangement on the growth surface of a plane inclined by about 45 degrees in the m-axis direction as an example. FIG. 29 is a drawing showing a growth surface composed of micro steps formed from a {10-11} plane and an m-plane. FIG. 30 is a drawing showing a surface atomic arrangement of a surface obtained by inclining the c-plane with an off angle of 75 degrees in the m-axis direction as an example. FIG. 31 is a diagram showing the relationship between In incorporation and off-angle. FIG. 32 is a drawing showing the characteristics of each surface and angle range for In uptake, In segregation, and piezoelectric field. FIG. 33 is a drawing showing the detailed characteristics of each surface and angle range for In uptake, In segregation, and piezoelectric field.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, embodiments of the GaN-based semiconductor optical device, the method for manufacturing the GaN-based semiconductor optical device, the epitaxial substrate, and the method for growing the GaN-based semiconductor region of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals. In this description, regarding the a1 axis, a2 axis, a3 axis, and c axis indicating the crystal axes of the hexagonal crystal, for example, the [000-1] axis is used to indicate the direction opposite to the positive direction of each crystal axis. Is the reverse direction of the [0001] axis, and "-1" with a negative sign in front of a number (for example, "1") is used to indicate the reverse direction.

  FIG. 1 schematically shows the structure of a GaN-based semiconductor optical device according to the present embodiment. Examples of the GaN based semiconductor optical device 11a include a light emitting diode. FIG. 2 is a drawing schematically showing the structure of the GaN-based semiconductor optical device according to the present embodiment. Examples of the GaN-based semiconductor optical device 11b include a semiconductor laser. FIG. 3 is a diagram showing a template structure in the GaN-based semiconductor optical device shown in FIGS. 1 and 2.

  Referring to FIGS. 1 and 2, the GaN-based semiconductor optical devices 11 a and 11 b include a template 13, a GaN-based semiconductor epitaxial region 15, and an active layer 17. The template 13 includes a support 131, a mask 133, a recess 135, and a semiconductor region 139. The support 131 is made of a material different from that of the gallium nitride based semiconductor and has a main surface 131a. A semiconductor region 139 is provided on the support 131, and the main surface 139 a provides the main surface 13 a of the template 13. The main surface 139a of the semiconductor region 139 of the template 13 is 63 in the direction of the m-axis of the first gallium nitride semiconductor from the plane orthogonal to the reference axis Cx extending along the c-axis of the first gallium nitride semiconductor. It is inclined at an inclination angle in the range of not less than 80 degrees and less than 80 degrees.

  In the template 13, the mask 133 has openings 133a and stripes 133b. The stripe 133b can be made of a silicon-based inorganic insulator such as silicon oxide. The mask 133 covers the main surface 131a, and a recess 135 is located in the opening 133a of the mask 133. The recess 135 is provided in the opening 133a of the mask 133, and has first and second side surfaces 135a and 135b. The first and second side surfaces 135a and 135b are inclined with respect to the main surface 131a. In the present embodiment, the stripe 133b and the recess 135 of the mask 133 are adjacent to each other, and the stripe 133b and the recess 135 and the first and second side surfaces 135a and 135b extend in one direction (for example, the X-axis direction). ing. This direction is preferably a direction orthogonal to the inclination direction of the c-axis, for example. The insulator 137 covers the second side surface 135b. The insulator 137 can be made of a silicon-based inorganic insulator such as silicon oxide. The semiconductor region 139 is provided on the first and second side surfaces 135a and 135b and embeds the mask 133 and the insulator 137 therein. Therefore, the semiconductor region 139 covers the side surface 133c and the upper surface 133d of the mask 133, and covers the insulator 137 and the first side surface 135a. Since the semiconductor region 139 is selectively grown on the first side surface 135a of the recess 135 with respect to the second side surface 135b, the semiconductor region 139 covers the first side surface 135a. The semiconductor region 139 can include a semiconductor region epitaxially grown in the c-axis direction of the first gallium nitride based semiconductor. The plane orientation of the main surface 139a of the semiconductor region 139 can be defined by the intersection angle AG between the first side surface 135a of the support 131 and the main surface 131a of the support 131.

  The support 131 can be made of a material having a crystal structure such as a wurtzite structure (hexagonal crystal), a zinc blende structure, a diamond structure, a triclinic structure, or a spinel crystal structure. The support 131 can be made of any of spinel, sapphire, zinc oxide, silicon carbide, silicon, and gallium oxide. These materials can provide a template with a semiconductor region of a main surface inclined at an inclination angle in a range of 63 degrees or more and less than 80 degrees.

When the support 131 is made of a heterogeneous substrate such as sapphire, 6H—SiC, 4H—SiC, or ZnO, the first side surface 135a can be a {0001} plane. The semiconductor region 139 grows epitaxially on, for example, a sapphire {0001} plane. The normal axis of the first side surface 135a faces the c-axis direction of the first gallium nitride semiconductor. When the support 131 is made of a different substrate such as silicon, 3C—SiC, spinel (eg, MgAl ₂ O ₄ ), the first side surface 135a can be a {111} plane. The semiconductor region 139 grows epitaxially on the heterogeneous substrate {111} plane. The normal axis of the first side surface 135a faces the c-axis direction of the first gallium nitride semiconductor. Furthermore, when the support 131 is made of a heterogeneous substrate such as gallium oxide (for example, β-Ga ₂ O ₃ ), the first side surface 135a can be a gallium oxide a surface. The semiconductor region 139 grows epitaxially on the different substrate a surface. The first side surface 135a grows in the c-axis direction of the first gallium nitride based semiconductor.

  The angle formed between the reference plane extending along the main surface 131a of the support 131 and the first side surface 135a is 63 in the direction of the m-axis of the first gallium nitride semiconductor from the plane orthogonal to the reference axis Cx. It is in the range of not less than 80 degrees and less than 80 degrees.

  The length of the short side L1 of the opening 133a can be 0.5 micrometers or more. A first side for epitaxial growth can be defined. Further, the length of the short side L1 can be 5 micrometers or less. According to the size of the opening 133a of the mask 133, the semiconductor region 139 of the main surface 139a inclined at an inclination angle in the range of not less than 63 degrees and less than 80 degrees can be provided to the template 13.

  The short side L2 of the mask 133 can be 0.5 micrometers or more. First and second side surfaces for epitaxial growth are defined. In addition, the short side L2 of the mask 133 can be in a range of 5 micrometers or less. The size of the cover of the mask 133 is determined so that the template 13 can be provided with the semiconductor region 139 formed by integrally connecting the gallium nitride crystals grown from the adjacent openings 133a so as to cover the stripe 133b. In the template 13, the main surface 139a of the semiconductor region 139 is inclined with respect to the c-axis at an inclination angle in the range of not less than 63 degrees and less than 80 degrees.

  The openings 133a of the mask 133 can be periodically arranged. Further, the stripes 133b of the mask 133 can be periodically arranged.

The semiconductor region 139 can be made of In _S Al _T Ga _1- STN (0 ≦ S ≦ 1, 0 ≦ T ≦ 1, 0 ≦ S + T <1). The semiconductor region 139 is made of a first GaN-based semiconductor, and is preferably made of, for example, GaN, InGaN, AlGaN, or the like. Since GaN is a binary compound GaN-based semiconductor, it can provide good crystal quality and a stable template main surface. The first GaN-based semiconductor can be made of, for example, AlN.

  Referring to FIG. 1, the c-plane of the template 13 extends along the plane Sc. On the plane Sc, a coordinate system CR (c-axis, a-axis, m-axis) for indicating the crystal axes of the hexagonal GaN-based semiconductor is shown. The main surface 13a of the template 13 is not less than 63 degrees and less than 80 degrees in the direction of the m-axis of the first GaN-based semiconductor from the plane orthogonal to the reference axis Cx extending along the c-axis of the first GaN-based semiconductor. Inclined at an inclination angle of the range. The inclination angle α is defined by the angle formed between the normal vector VN of the main surface 13a of the template 13 and the reference axis Cx, and this angle α is equal to the angle formed by the vector VC + and the vector VN in this embodiment.

  The GaN-based semiconductor epitaxial region 15 is provided on the main surface 13a. The GaN-based semiconductor epitaxial region 15 can include one or more semiconductor layers. An active layer 17 is provided on the GaN-based semiconductor epitaxial region 15. The active layer 17 includes at least one semiconductor epitaxial layer 19. The semiconductor epitaxial layer 19 is provided on the GaN-based semiconductor epitaxial region 15. The semiconductor epitaxial layer 19 is made of a second GaN-based semiconductor containing indium, for example, InGaN, InAlGaN, or the like. The film thickness direction of the semiconductor epitaxial layer 19 is inclined with respect to the reference axis Cx. The reference axis Cx can be oriented in the direction of the [0001] axis of the first GaN-based semiconductor or the direction of the [000-1] axis. In the present embodiment, the reference axis Cx is oriented in the direction indicated by the vector VC +, and as a result, the vector VC− is oriented in the direction of the [000-1] axis.

  According to the GaN-based semiconductor optical device 11a, the main surface 13a of the template 13 having the inclination angle is composed of a surface morphology M1 including a plurality of narrow terraces as shown in FIG. Further, since the GaN-based semiconductor epitaxial region 15 is provided on the semiconductor region 139, the crystal axis of the GaN-based semiconductor epitaxial region 15 takes over the crystal axis in the semiconductor region 139 of the template 13. Therefore, the main surface 15a of the GaN-based semiconductor epitaxial region 15 is also inclined at an angle in the range of 63 degrees to less than 80 degrees in the m-axis direction from the plane orthogonal to the reference axis Cx. The main surface 15a also has a surface morphology M2 including a plurality of narrow terraces. The arrangement of these terraces constitutes a microstep. Since the terrace in the above angle range is narrow, nonuniformity of the In composition is unlikely to occur over a plurality of terraces. Therefore, a decrease in light emission characteristics due to In segregation is suppressed.

  Further, since the terrace structure is related to the tilt angle from the c-axis, a template whose tilt angle is defined based on the {0001} plane of the first GaN-based semiconductor, and the tilt angle is the first GaN In any of the templates defined on the basis of the {000-1} plane of the system semiconductor, a decrease in light emission characteristics is suppressed. In other words, even if the reference axis Cx is oriented in either the [0001] axis or the [000-1] axis of the first GaN-based semiconductor, a decrease in light emission characteristics is suppressed.

  In the GaN-based semiconductor optical device 11a, the main surface 13a of the template 13 is inclined at an angle in the range of 70 degrees or more and less than 80 degrees from the plane perpendicular to the reference axis in the m-axis direction of the first GaN-based semiconductor. Preferably it is. The substrate main surface 13a in this angular range has a plurality of terraces that are narrower.

  According to the GaN-based semiconductor optical device 11a, a decrease in light emission characteristics due to In segregation in the active layer 17 is suppressed.

  Referring to FIG. 1, a coordinate system S is shown. The main surface 13a of the template 13 faces the Z-axis direction and extends in the X direction and the Y direction. The X axis is in the direction of the a axis.

  The GaN-based semiconductor epitaxial region 15 can include one or a plurality of first conductivity type GaN-based semiconductor layers. In this embodiment, the GaN-based semiconductor epitaxial region 15 includes an n-type GaN semiconductor layer 23 and an n-type InGaN semiconductor layer 25 arranged in the Z direction. Since the n-type GaN semiconductor layer 23 and the n-type InGaN semiconductor layer 25 are epitaxially grown on the main surface 13a of the template 13, the main surface 23a of the n-type GaN semiconductor layer 23 and the main surface 25a of the n-type InGaN semiconductor layer 25 (this In the embodiment, the surface 15a) also has morphology M3, M2 each having a terrace structure.

  The morphology M1, M2, M3 has a plurality of microsteps arranged in the c-axis tilt direction, and these microsteps extend in a direction intersecting the tilt direction. The main constituent surfaces of the microstep include at least an m-plane and a {10-11} plane. In the above configuration surface and step end, In is well taken in.

  The GaN-based semiconductor optical device 11 a can include a GaN-based semiconductor region 21 provided on the active layer 17. The GaN-based semiconductor region 21 can include one or a plurality of second conductivity type GaN-based semiconductor layers. The GaN-based semiconductor region 21 includes an electron block layer 27 and a contact layer 29 arranged in the Z direction. The electron block layer 27 can be made of, for example, AlGaN, and the contact layer 29 can be made of, for example, p-type GaN or p-type AlGaN.

  In the GaN-based semiconductor optical device 11a, the active layer 17 is preferably provided so as to generate an emission wavelength of 370 nm or more. In segregation can be reduced in the range of the indium composition that achieves an active layer that generates light having a wavelength of 370 nm or longer. Moreover, it is preferable that the active layer 17 is provided so that the light emission wavelength which is 650 nm or less may be produced | generated. In an active layer that generates an emission wavelength of 650 nm or more, since the indium composition of the semiconductor epitaxial layer is large, it is difficult to obtain a semiconductor epitaxial layer having a desired crystal quality.

  The active layer 17 can have a quantum well structure 31, and the quantum well structure 31 includes well layers 33 and barrier layers 35 that are alternately arranged in a direction of a predetermined axis Ax. In this embodiment, the well layer 33 is made of the semiconductor epitaxial layer 19, and the well layer 33 is made of InGaN, InAlGaN, or the like, for example. The barrier layer 35 is made of a GaN-based semiconductor, and the GaN-based semiconductor can be made of, for example, GaN, InGaN, AlGaN, or the like. The n-type GaN-based semiconductor layers 23 and 25, the active layer 17, and the GaN-based semiconductor layers 27 and 29 are arranged in the direction of a predetermined axis Ax. The direction of the reference axis Cx is different from the direction of the predetermined axis Ax.

  According to this GaN-based semiconductor optical device 11a, small In segregation is achieved not only in the semiconductor epitaxial layer made of a single layer film but also in the quantum well structure 31.

  The GaN-based semiconductor optical device 11 a can include a first electrode 37 (for example, an anode) provided on the contact layer 29, and the first electrode 37 can include a transparent electrode that covers the contact layer 29. it can. For example, Ni / Au is used as the transparent electrode. When the support 131 of the template 13 is conductive, the GaN-based semiconductor optical device 11a can include a second electrode 39 (for example, a cathode) provided on the back surface 13b of the template 13, and the second The electrode 39 is made of, for example, Ti / Al. When the support 131 of the template 13 is not conductive, the second electrode 39 is provided so as to make ohmic contact with the exposed surface of the semiconductor region 139 partially exposed by etching or the like.

  The active layer 17 generates light LB1 in response to an external voltage applied across the electrodes 37 and 39. In this embodiment, the GaN-based semiconductor optical device 11a includes a surface light emitting device. In the active layer 17, the piezoelectric field is small.

The off angle A _OFF in the a-axis direction in the semiconductor region 139 of the template 13 is preferably a finite value. The off angle A _{OFF in the} a-axis direction improves the surface morphology of the epitaxial region. This off angle A _OFF is an angle in the XZ plane. The range of the off angle A _OFF can be, for example, a range of −3 degrees or more and +3 degrees or less. Specifically, the range of the off angle A _OFF is, for example, −3 degrees or more and −0.1 degrees or less and +0. It is preferably in the range of 1 degree or more and +3 degree or less. When the range of the off angle A _OFF is, for example, in a range of not less than −0.4 degrees and not more than −0.1 degrees and not less than +0.1 degrees and not more than +0.4 degrees, the surface morphology is further improved.

  In the GaN-based semiconductor optical device 11a, the active layer 17 is preferably provided so as to generate an emission wavelength of 480 nm or more. The active layer 17 is preferably provided so as to generate an emission wavelength of 600 nm or less. An inclination angle in a range of 63 degrees or more and less than 80 degrees is effective in a light emission wavelength range of 480 nm or more and 600 nm or less. At a long wavelength in this wavelength range, a large In composition is required for the well layer, and the emission intensity is greatly reduced on the surface showing large In segregation, such as the c-plane, m-plane and {10-11} plane. To do. On the other hand, since the In segregation is small in the angular range of the present embodiment, the decrease in emission intensity is small even in a long wavelength region of 480 nm or more.

Referring to FIG. 2, the GaN-based semiconductor optical device 11b includes a template 13, a GaN-based semiconductor epitaxial region 15, and an active layer 17, similarly to the GaN-based semiconductor optical device 11a. The c-plane of the template 13 extends along the plane Sc shown in FIG. On the plane Sc, a coordinate system CR (c-axis, a-axis, m-axis) is shown. The main surface 13a of the template 13 is not less than 63 degrees and less than 80 degrees in the direction of the m-axis of the first GaN-based semiconductor from the plane orthogonal to the reference axis Cx extending along the c-axis of the first GaN-based semiconductor. Inclined at an inclination angle of the range. The inclination angle α is defined by the angle formed between the normal vector VN of the main surface 13a of the template 13 and the reference axis Cx, and this angle is equal to the angle formed by the vector VC + and the vector VN in this embodiment. The GaN-based semiconductor epitaxial region 15 is provided on the main surface 13a. The active layer 17 includes at least one semiconductor epitaxial layer 19. The semiconductor epitaxial layer 19 is provided on the GaN-based semiconductor epitaxial region 15. The semiconductor epitaxial layer 19 is made of a second GaN-based semiconductor, and the second GaN-based semiconductor contains indium as a constituent element. The film thickness direction of the semiconductor epitaxial layer 19 is inclined with respect to the reference axis Cx. The reference axis Cx can be oriented in the direction of the [0001] axis of the first GaN-based semiconductor or the direction of the [000-1] axis. In the present embodiment, the reference axis Cx is oriented in the direction indicated by the vector VC +, and as a result, the vector VC− is oriented in the direction of the [000-1] axis. FIG. 2 also shows an off angle A _OFF , and this off angle A _OFF is an angle in the XZ plane.

  According to the GaN-based semiconductor optical device 11b, in the template 13, the main surface 13a (the main surface 139a of the semiconductor region 139 shown in FIG. 3) has a plurality of narrow terraces as shown in FIG. Containing surface morphology M1. A GaN-based semiconductor epitaxial region 15 is provided on the semiconductor region 139 of the template 13. The crystal axis of the GaN-based semiconductor epitaxial region 15 inherits the crystal axis of the semiconductor region 139 in the template 13. Therefore, the main surface 15a of the GaN-based semiconductor epitaxial region 15 is also inclined at an angle in the range of 63 degrees to less than 80 degrees in the m-axis direction from the plane orthogonal to the reference axis Cx. Accordingly, the main surface 15a of the GaN-based semiconductor epitaxial region 15 also has a surface morphology M2 including a plurality of narrow terraces. The arrangement of these terraces constitutes a microstep. Since the terrace in the above angle range is narrow, nonuniformity of the In composition is unlikely to occur over a plurality of terraces. Therefore, a decrease in light emission characteristics due to In segregation is suppressed.

  In one embodiment of the GaN-based semiconductor optical device 11b, the GaN-based semiconductor epitaxial region 15 includes an n-type cladding layer 41 and a light guide layer 43a arranged in the direction of the Ax axis (Z direction). The n-type cladding layer 41 can be made of, for example, AlGaN or GaN, and the light guide layer 43a can be made of, for example, undoped InGaN. Since the n-type cladding layer 41 and the light guide layer 43a are epitaxially grown on the main surface 13a of the template 13 (the main surface 139a of the semiconductor region 139 shown in FIG. 3), the main surface 41a of the n-type cladding layer 41 and the light The main surface 43c of the guide layer 43a (equivalent to the surface 15a in this embodiment) also has a surface morphology having a terrace structure. The surface morphology has a plurality of microsteps arranged in the c-axis tilt direction, and these microsteps extend in a direction intersecting the tilt direction. The main constituent surfaces of the microstep include at least an m-plane and a {10-11} plane. In the above configuration surface and step end, In is well taken in.

  In the GaN-based semiconductor optical device 11b, the GaN-based semiconductor region 21 includes a light guide layer 43b, an electron block layer 45, a cladding layer 47, and a contact layer 49 arranged in the Z direction. The light guide layer 43b can be made of undoped InGaN, for example. The electron block layer 45 can be made of, for example, AlGaN, the clad layer 47 can be made of, for example, p-type AlGaN or p-type GaN, and the contact layer 49 can be made of, for example, p-type GaN or p-type AlGaN. Can do.

  The GaN-based semiconductor optical device 11 b can include a first electrode 51 (for example, an anode) provided on the contact layer 49, and the first electrode 51 is a stripe window of the insulating film 53 that covers the contact layer 49. Is connected to the contact layer 49. For example, Ni / Au is used as the first electrode 51. When the support 131 of the template 13 is conductive, the GaN-based semiconductor optical device 11b can include a second electrode 55 (for example, a cathode) provided on the back surface 13b of the template 13, and the second The electrode 55 is made of, for example, Ti / Al. When the support 131 of the template 13 does not have conductivity, the second electrode 55 is provided to make ohmic contact with the exposed surface of the semiconductor region 139 partially exposed by etching or the like.

  The active layer 17 generates light LB2 in response to an external voltage applied to both ends of the electrodes 51 and 55. In this embodiment, the GaN-based semiconductor optical device 11b includes an end surface light emitting device. In the active layer 17, the Z component of the piezoelectric field (component relating to the direction of the predetermined axis Ax) is a direction from the p-type GaN-based semiconductor layers 43 a, 45, 47, 49 to the n-type GaN-based semiconductor layers 41, 43 a. The reverse direction. According to the GaN-based semiconductor optical device 11b, since the Z component of the piezoelectric field is opposite to the direction of the electric field due to the external voltage applied to both ends of the electrodes 51 and 55, the shift of the emission wavelength is reduced.

In the GaN-based semiconductor optical devices 11a and 11b, the off angle A _OFF in the a-axis direction in the template 13 is preferably a finite value. The off angle A _{OFF in the} a-axis direction improves the surface morphology of the epitaxial region. The range of the off angle A _OFF can be, for example, a range of −3 degrees or more and +3 degrees or less. Specifically, the range of the off angle A _OFF is, for example, −3 degrees or more and −0.1 degrees or less and +0. It is preferably in the range of 1 degree or more and +3 degree or less. When the range of the off angle A _OFF is, for example, in a range of not less than −0.4 degrees and not more than −0.1 degrees and not less than +0.1 degrees and not more than +0.4 degrees, the surface morphology is further improved.

In the GaN-based semiconductor optical devices 11a and 11b, the active layer 17 is preferably provided so as to generate an emission wavelength of 480 nm or more. The active layer 17 is preferably provided so as to generate an emission wavelength of 600 nm or less. An inclination angle in a range of 63 degrees or more and less than 80 degrees is effective in a light emission wavelength range of 480 nm to 600 nm. When this wavelength is reached, the In composition of the well layer is considerably increased, and the emission intensity is greatly reduced on the surface of large In segregation such as the c-plane, m-plane and {10-11} plane. On the other hand, since the In segregation is small in this angular range, the decrease in emission intensity is small even in the long wavelength region of 480 nm or more. The range of the thickness of the well layer can be, for example, 0.5 nm to 10 nm. The range of the In composition X of the In _X Ga _1-X N well layer can be, for example, 0.01 to 0.50.

  Next, the production of the template will be described. FIG. 4 is a drawing showing a process flow including main processes in the production of a template. 5 and 6 are drawings schematically showing main steps in the production of a template. FIG. 7 is a drawing schematically showing the inclination angle of the main surface of the dissimilar substrate for obtaining a template having a desired inclination angle.

  In step S120, a heterogeneous substrate 141 is prepared. In the following description, the dissimilar substrate 141 is made of, for example, sapphire. As shown in FIG. 5A, the normal line N of the main surface 141a of the heterogeneous substrate 141 forms an angle γ with the c-axis. In the embodiment, the angle γ is selected within the range of the angle α.

  In step S121, a dielectric film for a mask is grown on the main surface 141a of the heterogeneous substrate 141. The film thickness of the dielectric film can be, for example, 10 nanometers or more, and can be 500 nanometers. Next, as shown in FIG. 5B, in step S122, a mask 143 is formed by processing the dielectric film using photolithography and etching. In this embodiment, the mask 143 includes a stripe 143a. In the preferred embodiment, the stripes 143a extend in a direction perpendicular to the c-axis of the gallium nitride based semiconductor grown on the template and are arranged in the inclined direction of the c-axis. In step S123, the heterogeneous substrate 141 is etched using the mask 143 to form the support 145. Etching can be dry etching. By this etching, a recess 147 is formed in the main surface 141a of the different substrate 141. On the support 145, stripes 143a and recesses 147 are alternately arranged. The stripe 143 a covers the main surface 145 a of the support 145. The recesses 147 extend in a direction perpendicular to the c-axis of the gallium nitride based semiconductor grown on the template, and are arranged in the inclination direction of the c-axis. The recess 147 includes first and second side surfaces 147a and 147b, the first side surface 147a has a predetermined surface orientation, and the second side surface 147b forms a predetermined surface orientation on the first side surface 147a. It is formed in such a plane orientation. The plane orientation of the first side surface 147a defines the inclination angle of the c-axis of a gallium nitride based semiconductor grown in a later step. When the heterogeneous substrate 141 is made of sapphire, the first side surface 147a is made of a {0001} surface, and the second side surface 147b is made of a facet surface. As shown in FIG. 5C, the first side surface 147a intersects with the c-axis Cx, and is substantially orthogonal to the c-axis Cx in this embodiment.

  In step S124, as shown in FIG. 6A, the insulating film 149 is formed on the second side surface 147b so as to cover the second side surface 147b, and the first side surface 147a is not covered. The side surface 147a is exposed. The selective formation of the insulating film 149 is performed by, for example, film deposition, photolithography, and etching. The film thickness of this insulating film can be, for example, 10 nanometers or more, and can be 500 nanometers or less.

  In step S125, an integrated gallium nitride based semiconductor is grown on the support 145 so as to cover the mask 143, thereby forming a single crystal semiconductor region. This semiconductor region is formed by epitaxial growth of the recess 147 on the first side surface 147a. In step S125-1, as shown in FIG. 6B, a gallium nitride based semiconductor is grown to fill the recess 147 at a relatively low temperature, for example, about 500 degrees Celsius. In this growth, since the gallium nitride semiconductor is epitaxially grown on the side surface 147a in each recess 147, the c-axis of the gallium nitride semiconductor is inclined at an angle γ with respect to the main surface of the support 145. Yes. Next, in step S125-2, as shown in FIG. 6C, the crystal axis of the gallium nitride semiconductor in which the recess 147 is filled is taken over at a relatively high temperature, for example, about 1100 degrees Celsius, and the same type of nitriding is performed. Growing gallium-based semiconductors. This growth is performed under conditions that promote the lateral growth of the gallium nitride-based semiconductor as compared to the growth in step S125-1. Through these steps, a single crystal semiconductor region 151 is formed over the support 145 so as to cover the mask 143 and the insulating film 149. In a preferred embodiment, the single crystal semiconductor region 151 can be made of GaN, and this template is called a GaN template.

The material of the heterogeneous substrate 141 is not limited to sapphire, and can be any of spinel, zinc oxide, silicon carbide, silicon, and gallium oxide. These materials can provide a template with a semiconductor region of a main surface inclined at an inclination angle in a range of 63 degrees or more and less than 80 degrees. FIG. 7 is a drawing showing the relationship between the main surface of a different substrate and the crystal axes of the material. Referring to FIG. 7A, in silicon, the crystal axis <111> forms an angle γ with the normal N of the main surface. The crystal axis <111> is inclined at an angle γ in the direction of the <−101> axis. In order to form the recess in the silicon, the etchant can be, for example, KOH. Referring to FIG. 7B, in 4H—SiC and 6H—SiC, the crystal axis <0001> forms an angle γ with the normal N of the main surface. The crystal axis <0001> is inclined at an angle γ in the direction of the <1-100> axis. Dry etching can be performed to form a recess in 4H—SiC or 6H—SiC. Referring to FIG. 7C, in 3C-SiC, the crystal axis <111> forms an angle γ with the normal line N of the main surface. The crystal axis <111> is inclined at an angle γ in the direction of the <−101> axis. Dry etching can be performed to form a recess in 3C-SiC. Referring to FIG. 7D, in ZnO, the crystal axis <0001> forms an angle γ with the normal N of the main surface. The crystal axis <0001> is inclined at an angle γ in the direction of the <1-100> axis. In order to form a recess in ZnO, the etchant can be, for example, nitric acid. Referring to FIG. 7E, in the spinel, the crystal axis <111> forms an angle γ with the normal N of the main surface. The crystal axis <111> is inclined at an angle γ in the direction of the <−101> axis. Dry etching can be performed to form recesses in the spinel. Referring to FIG. 7F, in β-Ga ₂ O ₃ , the c-axis forms an angle γ with the main surface. The c-axis forms an angle of 103.7 degrees with respect to the a-axis. In order to form the recess in β-Ga ₂ O ₃ , the etchant can be, for example, hydrofluoric acid.

  Using this template, an epitaxial substrate for a gallium nitride based semiconductor optical device is provided. An epitaxial substrate includes a template for the above-described gallium nitride based semiconductor optical device, a gallium nitride based semiconductor epitaxial region provided on the template, and a semiconductor for an active layer provided on the gallium nitride based semiconductor epitaxial region. An epitaxial layer. An epitaxial substrate for a gallium nitride-based semiconductor light-emitting element that is provided on a different substrate made of a material different from that of a gallium nitride-based semiconductor and that can suppress a decrease in light emission characteristics due to In segregation is provided.

Example 1
In Example 1, a GaN wafer was used in place of the GaN template as a preliminary experiment. According to the knowledge of the inventors, the experiment using the GaN wafer can provide the same result as the experiment using the GaN template. A GaN wafer S1 and a GaN wafer S2 were prepared. The main surface of the GaN wafer S1 is a c-plane in hexagonal GaN. The main surface of the GaN wafer S2 is inclined at an angle of 75 degrees from the c-plane in the m-axis direction in hexagonal GaN, and this inclined surface is shown as a (20-21) plane. All main surfaces are mirror-polished. On the main surface of the wafer S2, the off angles are distributed from the (20-21) plane at an angle in the range of −3 degrees to +3 degrees.

An Si-doped n-type GaN layer and an undoped InGaN layer were epitaxially grown on the GaN wafer S1 and the GaN wafer S2 by metal organic vapor phase epitaxy to produce epitaxial substrates E1 and E2 shown in FIG. Trimethyl gallium (TMG), trimethyl indium (TMI), ammonia (NH ₃ ), and silane (SiH ₄ ) were used as raw materials for epitaxial growth.

Wafers S1 and S2 were placed in the growth furnace. Epitaxial growth was performed on these wafers under the following conditions. A heat treatment was performed for 10 minutes while flowing NH ₃ and H ₂ at a temperature of 1050 degrees Celsius and an in-furnace pressure of 27 kPa. As this heat treatment temperature, for example, a temperature of 850 to 1150 degrees Celsius can be used. Further, a combination of NH ₃ and H ₂ can be used as the atmosphere for the heat treatment. By the surface modification by this heat treatment, a terrace structure defined by the off angle is formed on the surface of the wafer S2.

After this heat treatment, TMG, NH ₃ and SiH ₄ were supplied to the growth reactor to grow Si-doped GaN layers 61a and 61b at 1000 degrees Celsius. The thickness of the GaN layers 61a and 61b is, for example, 2 micrometers. Next, TMG, TMI, and NH ₃ were supplied to the growth reactor to grow undoped InGaN layers 63a and 63b at a substrate temperature of 750 degrees Celsius. The thickness of the InGaN layers 63a and 63b is 20 nm. Further, the molar ratio is V / III = 7322, and the growth furnace pressure is 100 kPa. After the film formation, the temperature of the growth furnace was lowered to room temperature to produce epitaxial substrates E1 and E2.

  X-ray diffraction measurement of the epitaxial substrates E1 and E2 was performed. The scan was performed using the ω-2θ method. Since the X-ray diffraction angle reflects the lattice constant of the crystal, for example, the molar fraction of each element of the InGaN ternary mixed crystal can be measured.

  In addition, in the epitaxial substrates E1 and E2, since the off angles of the main surfaces of the wafers are different from each other, when performing X-ray diffraction measurement, the X-ray incidence device, A sample stage and an X-ray detector were arranged.

  Specifically, the epitaxial substrate E1 was axially aligned in the [0001] direction. The In composition in InGaN is determined by fitting the diffraction result with theoretical calculation. In this plane orientation, the normal direction [0001] of the main surface of the wafer coincides with the measurement axis direction [0001], so the values obtained from the theoretical calculation can be used as they are as the actual composition.

  The epitaxial substrate E2 is axially aligned in the [10-10] direction. With this shafting, X-rays are incident with an inclination of 15 degrees with respect to the wafer main surface {20-21} plane, so the value from X-ray diffraction underestimates the In composition. For this reason, when fitting an experimental result with theoretical calculation, it is necessary to correct | amend a measured value according to the inclination from a [10-10] direction. By this correction, the In composition in InGaN is determined.

  FIG. 9 is a drawing showing the results of X-ray diffraction and theoretical calculations. Referring to FIG. 9A, an experimental result EX1 and a theoretical calculation result TH1 of the epitaxial substrate E1 are shown. Referring to FIG. 9B, an experimental result EX2 and a theoretical calculation result TH2 of the epitaxial substrate E2 are shown. The In composition of the epitaxial substrate E1 is 20.5 percent, while the In composition of the epitaxial substrate E2 is 19.6 percent. This experimental result indicates that the GaN (20-21) plane has the same In incorporation compared to the c-plane of GaN. This is suitable for a long-wavelength light-emitting element that requires a high In composition in the production of optical devices such as light-emitting diodes and semiconductor laser diodes. Further, if the In composition is the same, the growth temperature of InGaN can be increased, and the crystallinity of the light emitting layer can be improved.

(Example 2)
In accordance with the steps shown in FIG. 10, the epitaxial substrates of the light-emitting diode structures (LED1, LED2) shown in FIGS. 11 (a) and 11 (b) are formed on the GaN template S3 and the GaN template S4 by metal organic vapor phase epitaxy, respectively. Made above. Use as a raw material for epitaxial growth, trimethyl gallium (TMG), trimethyl indium (TMI), trimethyl aluminum (TMA), ammonia _(NH 3), silane _(SiH 4), biscyclopentadienyl magnesium _(Cp 2 Mg) It was.

  GaN templates S3 and S4 were prepared. In this embodiment, the conductive material of the support of the GaN templates S3 and S4 is made of, for example, silicon. In step S101, a GaN template S3 having a principal surface made of a c-plane in hexagonal GaN was prepared. In step S102, a GaN template S4 corresponding to an inclination angle within a range of an inclination angle of 63 degrees to less than 80 degrees was prepared. In this example, the GaN template S4 has a GaN main surface inclined at an angle of 75 degrees from the c-plane in the m-axis direction in hexagonal GaN, and this inclined surface is shown as a (20-21) plane. It is.

Epitaxial growth was performed on the templates S3 and S4 under the following conditions. First, in step S103, the templates S3 and S4 were installed in the growth furnace. In step S104, a GaN-based semiconductor region is grown. For example, at 1100 degrees Celsius, TMG, NH ₃ and SiH ₄ were supplied to the growth reactor to grow the Si-doped GaN layer 65b. The thickness of the GaN layer 65b is, for example, 5 micrometers. Next, TMG, TMI, NH ₃ and SiH ₄ were supplied to the growth reactor at a substrate temperature of 850 degrees Celsius to grow the Si-doped InGaN layer 67b. The thickness of the InGaN layer 67b is 100 nm. The In composition of the InGaN layer 67b is, for example, 0.02.

In step S105, an active layer is grown. In step S106, TMG and NH ₃ were supplied to the growth reactor at a substrate temperature of 870 degrees Celsius, and the undoped GaN barrier layer 69b was grown at the growth temperature T1. The thickness of the GaN layer 69b is 15 nm. In step S107, after the growth, the growth is interrupted, and the substrate temperature is changed from 870 degrees Celsius to 760 degrees Celsius. After the change, in step S108, TMG, TMI, and NH ₃ were supplied to the growth reactor at the growth temperature T2 to grow the undoped InGaN well layer 71b. The thickness of the InGaN well layer 71b is 3 nm. The In composition of the InGaN layer 71b is, for example, 0.25. In the well layer 71b, the In flow rate is changed according to the emission wavelength. After the growth of the InGaN well layer 71b, the supply of TMI was stopped. In step S109, the substrate temperature was changed from 760 degrees Celsius to 870 degrees Celsius while supplying TMG and NH ₃ to the growth reactor. During this change, a part of the undoped GaN barrier layer 73b is grown. After the change, the remainder of the undoped GaN barrier layer 73b was grown in step S110. The thickness of the GaN barrier layer 73b is 15 nm. In step S111, the growth of the barrier layer, the temperature change, and the growth of the well layer were repeated to form the InGaN well layers (75b, 79b) and the GaN barrier layers (77b, 81b).

In step S112, a GaN-based semiconductor region is grown. For example, after the growth of the GaN barrier layer 81b, the supply of TMG was stopped and the substrate temperature was raised to 1000 degrees Celsius. At this temperature, TMG, TMA, NH ₃ and Cp ₂ Mg were supplied to the growth reactor to grow the p-type AlGaN electron blocking layer 83b. The Al composition of the electron block layer 83b was, for example, 0.18, and the electron block layer 83b was, for example, 20 nm. Thereafter, the supply of TMA was stopped, and the p-type GaN contact layer 85b was grown. The p-type GaN contact layer 85b was 50 nm, for example. After the film formation, the temperature of the growth furnace was lowered to room temperature to produce an epitaxial substrate E4. The growth temperature of the p-type region in this example is about 100 degrees lower than the growth temperature optimum for the growth of the p-type region on the c-plane. The inventors have confirmed that the following: The active layer formed on the substrate within the off-angle range is sensitive to temperature rise during the growth of the p layer and easily deteriorates. At the optimum temperature for the growth of the mold region, the macro dark region spreads, particularly when a long wavelength active layer is grown. Here, the dark region means a non-light emitting region in the fluorescence microscope image. By reducing the p-layer growth temperature, it was possible to prevent the dark region from spreading due to the temperature rise during the p-layer growth.

  Next, for the template S3, using the same film forming conditions, a Si-doped GaN layer (thickness: 5 micrometers) 65a, a Si-doped InGaN layer (thickness: 100 nm) 67a, and a p-type AlGaN electron blocking layer (thickness: 20 nm) 83a and a p-type GaN contact layer (thickness: 50 nm) 85a. The active layer includes InGan well layers (thickness: 3 nm) 71a, 75a, 79a, and GaN barrier layers (thickness: 15 nm) 69a, 73a, 77a, 81a. After the growth of the contact layer, the temperature of the growth furnace was lowered to room temperature to produce an epitaxial substrate E3.

  In step S113, electrodes were formed on the epitaxial substrates E3 and E4. First, a mesa shape was formed by etching (for example, RIE). The size of the mesa shape is, for example, 400 μm square. Next, p transparent electrodes (Ni / Au) 87a and 87b were formed on the p-type GaN contact layers 85a and 85b. Thereafter, a p-pad electrode (Ti / Au) was formed. In the Si-doped GaN layers 65a and 65b of the templates S3 and S4, n electrodes (Ti / Al) 89a and 89b are formed on the exposed surfaces 65c and 65d formed by etching. The procedure was an electrode annealing (for example, 550 degrees Celsius for 1 minute). Through these steps, light-emitting diode structures LED1 and LED2 were obtained.

An electroluminescence spectrum was measured by applying current to the light emitting diode structures LED1 and LED2. The electrode size is 400 micrometers square and the applied current is 120 mA. FIG. 12 is a diagram showing electroluminescence spectra of the light emitting diode structures LED1 and LED2. The spectra EL _C and EL _M75 are shown. Peak wavelength of these spectra are comparable, the peak intensity of the spectrum EL _M75 is more than twice the peak intensity of the spectrum EL _C, and in less than half the full width at half maximum of the spectrum EL _M75 is the full width at half maximum of the spectrum EL _C is there. The light output of the light emitting diode structure LED2 is high, and the full width at half maximum is small. These exhibit excellent color purity and can enhance color rendering when mixed with light emission of other colors. The full width at half maximum of light emission in the LED mode is small, which is very effective for lowering the threshold value of the laser diode.

  FIG. 13 is a drawing showing cathodoluminescence (CL) images of the epitaxial substrates E3 and E4. Referring to FIG. 13A, a cathodoluminescence image of the epitaxial substrate E3 is shown. It can be seen that the light emission image of FIG. 13A is uneven and the dark region that does not contribute to light emission is wide. This non-uniform emission is considered to be due to In segregation in the active layer of the epitaxial substrate E3. In an epitaxial substrate using a c-plane substrate, the degree of non-uniformity of light emission becomes more prominent as the emission wavelength becomes longer. Therefore, in a light emitting element using a c-plane substrate, the longer the wavelength of light emission, the lower the light output and the full width at half maximum of the emission spectrum.

  Referring to FIG. 13B, a cathodoluminescence image of the epitaxial substrate E4 is shown. The light emission image in FIG. 13B is superior in light emission uniformity compared to the light emission image in FIG. Therefore, in the epitaxial substrate E4, In segregation of the InGaN layer is considered to be small. For this reason, the light emission intensity of the light emitting element is large and the light emission half width is also small. In addition, in the light emitting device manufactured on the template S4, the decrease in light output in the long wavelength light emission is small, and the increase in half width in the long wavelength emission spectrum is also small.

  FIG. 14 is a drawing showing the measurement of the relationship between the emission wavelength and the current injection amount in the light emitting diode structures LED1 and LED2. Referring to FIG. 14, in the light emitting diode structure LED1, the emission wavelength gradually shifts to a short wavelength as the current injection amount is increased. On the other hand, in the light emitting diode structure LED2, after the light emission wavelength is slightly shifted to a short wavelength when the current injection amount is small, the light emission wavelength hardly changes with an increase in the current amount. This indicates that there is almost no fluctuation in the emission wavelength when changing the light emission intensity of the light emitting diode by changing the amount of current applied to the light emitting diode. That is, in the light emitting diode structure LED2, the current dependency of the emission peak wavelength in the LED mode is reduced.

  In the light emission measurement by light excitation, the light emission wavelength of the light emitting diode structure LED1 (c-plane) was 550 nm, and the light emission wavelength of the light emitting diode structure (75 degrees off) LED2 was 505 nm. The internal state of the light-emitting diode structure that is photoexcited corresponds to the internal state of the light-emitting diode structure into which a very small current is injected.

  From the dependence of the emission wavelength on the current injection and the emission measurement result by photoexcitation, the following is meant: In the light emitting diode structure LED2, when the applied voltage is gradually increased, the emission is very small (practical) In terms of generality, the shift of the emission wavelength is substantially completed “before light emission”), and the emission wavelength hardly shifts after the emission of sufficient intensity occurs.

  The piezo electric field in the active layer on the c-plane is piezo electric in the active layer provided on the GaN-based semiconductor surface inclined at an inclination angle in the range of 63 degrees to less than 80 degrees from the c-plane in the m-axis direction of the GaN-based semiconductor. Larger than the electric field. From the characteristics shown in FIG. 14, the direction of the piezoelectric field in the light emitting diode structure LED2 is opposite to the direction of the piezoelectric field in the light emitting diode structure LED1. The direction of the electric field at the time of current injection is opposite to the direction of the piezoelectric field in the light emitting diode structure LED2. FIG. 15 is a diagram showing calculation results shown in Non-Patent Documents 1 and 2. The difference between positive and negative in the curves representing the piezoelectric field in FIGS. 15A and 15B is the problem of the definition of the direction of the electric field. The slopes and curvatures of the curves are different because the parameters used for the calculation are different.

(Example 3)
Light emitting diode structures LED3 and LED4 were fabricated on GaN templates S5 and S6 having main surfaces inclined at an angle of 75 degrees in the m-axis direction from the c-plane. The light emitting diode structures LED3 and LED4 have different emission wavelengths. The light emission wavelength in the light emitting diode structures LED3 and LED4 was changed by changing the In composition of the well layer. In order to change the In composition, the flow rate of the In raw material (for example, TMI) was changed during the growth of the well layer. Except for the change of the active layer, the light emitting diode structures LED3 and LED4 are manufactured in the same manner as the light emitting diode structure LED2.

FIG. 16 is a diagram showing electroluminescence of a well layer light emitting diode structure having different In compositions. The well layer of the light emitting diode structure LED3 is, for example, In _0.16 Ga _0.84 N, and the well layer of the light emitting diode structure LED4 is, for example, In _0.20 Ga _0.80 N. When the light emitting diode structure LED3 (peak wavelength: 460 nm) and the light emitting diode structure LED4 (peak wavelength: 482 nm) are compared, no difference in emission intensity or full width at half maximum is observed at these wavelengths. This is very suitable for producing a highly efficient long wavelength light emitting device.

  FIG. 17 is a diagram showing external quantum efficiency and human visibility curves in an InGaN well layer light emitting diode and an AlGaInP well layer light emitting diode. In order to obtain a light emitting diode structure that emits light having a long wavelength, a well layer having a large In composition is formed. According to the knowledge of the inventors, as shown in FIG. 17, in the light emitting diode structure on the c-plane GaN substrate, the crystallinity of InGaN decreases with the increase of the In composition of the InGaN well layer. This decrease in crystallinity reduces the emission intensity and increases the full width at half maximum of the spectrum. In particular, in a long wavelength region exceeding 500 nm, a light emitting element such as a light emitting diode with high external quantum efficiency cannot be produced.

  As already described, the light-emitting element includes a GaN-based semiconductor well layer containing an In element. It is grown on a GaN-based semiconductor surface that is inclined with respect to the c-plane at the corners. According to this light emitting element, no difference in light emission intensity or full width at half maximum is observed. This is very suitable for producing a highly efficient long wavelength light emitting device.

Example 4
An epitaxial substrate of the laser diode structure (LD1) shown in FIG. 18 was fabricated on the GaN template S5 having the same quality as the GaN template S4. Use as a raw material for epitaxial growth, trimethyl gallium (TMG), trimethyl indium (TMI), trimethyl aluminum (TMA), ammonia _(NH 3), silane _(SiH 4), biscyclopentadienyl magnesium _(Cp 2 Mg) It was.

  A GaN template S5 corresponding to an inclination angle within a range of an inclination angle of 63 degrees to less than 80 degrees was prepared. The GaN template S5 has a main surface inclined at an angle of 75 degrees from a plane orthogonal to the c-axis in the m-axis direction in hexagonal GaN, and this inclined surface is shown as a (20-21) plane. Epitaxial growth was performed on template S5 under the following conditions.

First, the template S5 was installed in the growth furnace. A GaN-based semiconductor region is grown on the template. For example, at 1150 degrees Celsius, TMG, TMA, NH ₃ , and SiH ₄ were supplied to the growth reactor to grow the n-type cladding layer 89. The n-type cladding layer 89 is, for example, a Si-doped AlGaN layer. The thickness of the AlGaN layer was, for example, 2 micrometers, and the Al composition thereof was, for example, 0.04.

Next, TMG, TMI, and NH ₃ were supplied to the growth reactor at a substrate temperature of 830 degrees Celsius to grow the optical guide layer 91a. The optical guide layer 91a is made of, for example, an undoped In _0.02 Ga _0.98 N layer, and has a thickness of 100 nm.

Next, the active layer 93 is grown. TMG and NH ₃ were supplied to the growth furnace at a substrate temperature of 870 degrees Celsius, and the GaN-based semiconductor barrier layer 93a was grown at the growth temperature T1. The barrier layer 93a is, for example, undoped GaN and has a thickness of 15 nm. After the growth of the barrier layer, the growth is interrupted and the substrate temperature is changed from 870 degrees Celsius to 830 degrees Celsius. At the growth temperature T2 after the change, TMG, TMI, and NH ₃ were supplied to the growth reactor to grow the undoped InGaN well layer 93b. Its thickness is 3 nm. After the well layer was grown, the substrate temperature was changed from 830 degrees Celsius to 870 degrees Celsius while TMI supply was stopped and TMG and NH ₃ were supplied to the growth reactor. Even during this change, a part of the undoped GaN barrier layer 93a is grown. After the temperature change was completed, the remainder of the undoped GaN barrier layer 93a was grown. The thickness of the GaN barrier layer 93a is 15 nm. Subsequently, the InGaN well layer 93b and the GaN barrier layer 93a were formed by repeating the growth of the barrier layer, the temperature change, and the growth of the well layer.

TMG, TMI, and NH ₃ were supplied to the growth reactor at a substrate temperature of 830 degrees Celsius to grow the light guide layer 91b on the active layer 93. The light guide layer 91b is made of, for example, an undoped InGaN layer. The thickness of the light guide layer 91b was 100 nm, and its In composition was 0.02.

A GaN-based semiconductor region is grown on the light guide layer 91b. After the growth of the light guide layer 91b, the supply of TMG and TMI was stopped, and the substrate temperature was raised to 1000 degrees Celsius. At this temperature, TMG, TMA, NH ₃ , and Cp ₂ Mg were supplied to the growth reactor to grow the electron block layer 95 and the p-type cladding layer 97. The electron block layer 95 is, for example, AlGaN. The thickness of the electron block layer 95 was 20 nm, for example, and the Al composition was 0.12. The p-type cladding layer 97 was, for example, Al _0.06 Ga _0.94 N. The thickness of the p-type cladding layer 97 was 400 nm, for example, and its Al composition was 0.06. Thereafter, the supply of TMA was stopped and the p-type contact layer 99 was grown. The p-type contact layer 99 is made of, for example, GaN and has a thickness of, for example, 50 nm. After the film formation, the temperature of the growth furnace was lowered to room temperature to produce an epitaxial substrate E5.

An electrode was formed on the epitaxial substrate E5. First, an insulating film 101 such as a silicon oxide film was deposited, and a contact window was formed on the insulating film by photolithography and etching. The contact window has a stripe shape, for example, and has a width of, for example, 10 micrometers. Next, a p-electrode (Ni / Au) 103 a was formed on the p-type GaN contact layer 99. Thereafter, a p-pad electrode (Ti / Au) was formed. An n-electrode (Ti / Al) 103b was formed on the back surface of the epitaxial substrate E5. A substrate product was produced by an electrode annealing procedure (for example, 550 degrees Celsius for 1 minute). After this process, the substrate product was cut at intervals of 800 micrometers to obtain a gain guide type laser diode LD5. The threshold current was 5 kAcm ⁻² . The oscillation wavelength at that time was 405 nm. In this semiconductor laser, the full width at half maximum of the emission spectrum in the LED mode is small. Further, the In segregation of the InGaN layer of this semiconductor laser is small. In addition, when the support body of template S5 does not have electroconductivity, n electrode 103b is provided so that an ohmic contact may be made with the exposed surface of template S5 partially exposed by etching or the like.

(Example 5)
In Example 5, as a preliminary experiment, a GaN wafer was used again instead of the GaN template. According to the knowledge of the inventors, the experiment using the GaN wafer can provide the same result as the experiment using the GaN template having the same plane orientation as that of the GaN wafer. InGaN was deposited on GaN wafers having various off angles, and the In composition of the InGaN was measured. FIG. 19 is a drawing showing the relationship between the In composition and the off angle of InGaN deposited on a GaN main surface having various inclination angles (off angles) taken from the c axis in the m-axis direction. Show off-angles in plots P1-P4:
Plot P1: 63 degree plot P2: 75 degree plot P3: 90 degree (m-plane)
Plot P4: 43 degrees Plot P5: 0 degrees (c-plane)
The In composition monotonously decreases with increasing off-angle from plot P5 (c-plane) to plot P4. On the other hand, plots P1 and P2 show In uptake equivalent to plot P5 (c-plane). Plot P3 (m-plane) also shows excellent In uptake, but there is a problem that In segregation increases at an off angle of 80 degrees or more, and the emission intensity decreases as the wavelength increases.

  With reference to FIG. 20A, the deposition of an In-containing GaN-based semiconductor on a GaN-based semiconductor surface having an off angle β in the range of 63 degrees to less than 80 degrees will be schematically described. On the semiconductor surface having an off-angle in the above-mentioned inclination angle range, for example, the surface near the {20-21} plane, a terrace T1 composed of {10-11} plane and a terrace T2 composed of m-plane appear. The semiconductor surface is composed of fine steps including these terraces T1 and T2. According to the experiments by the inventors, the In incorporation in the {10-11} plane as well as the m plane is equivalent to or superior to the In incorporation in the c plane. Further, in order to increase In incorporation, a sufficiently large terrace width that enables InN island-like growth is necessary.

  At an off angle in the range of 10 degrees to 50 degrees, a terrace T4 composed of {10-11} plane and a terrace T5 composed of c plane appear. The semiconductor surface is composed of fine steps composed of these terraces T4 and T5. In this angle range, the width of the terraces T4 and T5 decreases as the off-angle increases. Therefore, as shown in FIG. 19, the incorporation of In occurs at the off-angle semiconductor surface in the range of 10 to 50 degrees. small. This is because In is taken in on the terraces T4 and T5 when the step composed of the c-plane and the {10-11} plane is formed on the semiconductor surface. However, from the viewpoint of the bond of chemical bonds appearing at the terrace edge (step end) T6 composed of the terraces T4 and T5, In atoms are not taken in at the terrace edge T6.

  On the other hand, according to experiments by the inventors, the microstep structure composed of the terraces T1 and T2 has a good In uptake ability. This is because not only on the terraces T1 and T2, but also on the terrace edge (step end) T3 composed of the terraces T1 and T2, In is efficiently taken in. This is supported by the examination from the viewpoint of the bond of the chemical bond appearing on the terrace edge T3. The incorporated In is less likely to be detached from the semiconductor surface in a heat treatment (temperature increase between the growth of the well layer and the growth of the barrier layer) in an ammonia atmosphere. Therefore, for example, when the well layer made of InGaN is grown at the deposition temperature T1 and then raised to the growth temperature T2 of the barrier layer, the well layer is exposed from the surface of the well layer even if it is exposed to the furnace atmosphere. The amount of In released can be reduced.

  The semiconductor surface represented by the {20-21} plane in the example and having an off angle range of more than 50 degrees exhibits excellent In incorporation ability. Further, the light emission image from the active layer grown on the semiconductor surface has good uniformity. The half width of the emission spectrum is narrow, and the light output of the light emitting element is also high. In addition, even if a well layer having an increased In composition is formed to enable light emission at a long wavelength, a decrease in light emission efficiency is small. Therefore, the optical element and the manufacturing method thereof according to the present embodiment have very effective characteristics when realizing an optical element including an InGaN layer.

  As shown in FIG. 20A, a method for growing a GaN-based semiconductor film includes a step of preparing a GaN-based semiconductor region B having a surface having a plurality of microsteps, and a GaN-based semiconductor containing In as a constituent element. A film F is grown on the microstep surface. The microstep includes at least an m-plane and a {10-11} plane as main constituent surfaces. Alternatively, a method for growing a GaN-based semiconductor film includes a step of growing a semiconductor epitaxial region B made of a GaN-based semiconductor and having a main surface, and a GaN-based semiconductor film F containing In as a constituent element on the main surface of the semiconductor epitaxial region B. Grow up. The main surface of the semiconductor epitaxial region B has an inclination angle in a range of not less than 63 degrees and less than 80 degrees in the m-axis direction of the first GaN-based semiconductor from a plane orthogonal to the reference axis extending along the c-axis of the GaN-based semiconductor. It is inclined at.

An example of a microstep structure is shown. The height of the microstep structure is, for example, 0.3 nm or more, for example, 10 nm or less. The width is, for example, 0.3 nm or more, for example, 500 nm or less. The density is, for example, 2 × 10 ⁴ cm ⁻¹ or more, for example, 3.3 × 10 ⁷ cm ⁻¹ or less.

  The reason why small In segregation is realized at an off angle in the range of 63 degrees or more and less than 80 degrees can be explained as follows. In migration is possible on a large terrace composed of stable surfaces such as c-plane, m-plane (nonpolar plane), {11-22} plane, and {10-11} plane. Therefore, In atoms having a large atomic radius gather due to migration, and as a result, In segregation occurs. As shown in FIG. 13A, the cathodoluminescence image on the c-plane shows non-uniform light emission. On the other hand, in the crystal plane corresponding to the off angle within the range of 63 degrees or more and less than 80 degrees, for example, the {20-21} plane, the terraces T1 and T2 have a narrow terrace width, so In was taken in on the terraces T1 and T2. Sometimes sufficient In migration does not occur. Similarly, when In is taken in at the terrace edge T3, sufficient In migration does not occur. For this reason, it is taken into the crystal at the place where In is adsorbed during the deposition of atoms. In the deposition, In is adsorbed at random, as shown in FIG. 13B, the cathodoluminescence image on the {20-21} plane shows uniform light emission.

  The c-plane and m-plane show good In uptake as shown in FIG. However, large In segregation occurs, and particularly in a large In composition, In segregation increases, resulting in an increase in non-light-emitting regions due to non-uniform light emission images. By increasing the In composition of the active layer, the full width at half maximum of the emission spectrum becomes wider. On the other hand, at the off-angle between the c-plane and the {10-11} plane, In incorporation is reduced as compared with the c-plane, as shown in FIG. However, at the off angle between the {10-11} plane and the m plane, as shown in FIG. 19, In incorporation is better than the c plane, and In segregation is small.

  As described above, the range of the off angle of the crystal plane represented by the {20-21} plane shows good In uptake and small In segregation. Therefore, InGaN having very good crystallinity can be grown, and the In composition can be changed in a wider range than before depending on the emission wavelength. Therefore, a favorable optical element can be manufactured.

  Although the above description has been made with reference to the {20-21} plane, the same applies to the {20-2-1} plane. Further, the crystal planes and crystal orientations such as {20-21} plane, {10-11} plane, and m plane described in the above description are not only specified by the description itself but also crystallographically equivalent. The plane and orientation are also shown. For example, the {20-21} plane is a crystallographically equivalent plane of the (02-21) plane, the (0-221) plane, the (2-201) plane, the (−2021) plane, and the (−2201) plane. To represent.

(Example 6)
FIG. 21 is a drawing schematically showing a semiconductor laser in the present example. The semiconductor laser shown in FIG. 21 was produced as follows. First, a GaN template 110 having a (20-21) plane was prepared. The following semiconductor layers were epitaxially grown on the main surface (20-21) surface of the GaN semiconductor region of this GaN template.
n-type cladding layer 111: Si-doped InAlGaN, growth temperature 900 ° C., thickness 2 μm, Al composition 0.14, In composition 0.03;
Optical guide layer 112a: undoped GaN, growth temperature 840 degrees, thickness 250 nm;
Optical guide layer 112b: undoped InGaN, growth temperature 840 degrees, thickness 100 nm, In composition 0.03;
Active layer 113;
Barrier layer 113a: undoped GaN, growth temperature 870 degrees, thickness 15 nm;
Well layer 113b: undoped InGaN, growth temperature 730 degrees, thickness 3 nm, In composition 0.30;
Optical guide layer 114b: undoped InGaN, growth temperature 840 degrees, thickness 100 nm, In composition 0.03;
Electron blocking layer 115: Mg-doped AlGaN, growth temperature 1000 degrees, thickness 20 nm, Al composition 0.12;
Optical guide layer 114a: undoped GaN, growth temperature 840 degrees, thickness 250 nm;
p-type cladding layer 116: Mg-doped InAlGaN, growth temperature 900 degrees, thickness 400 nm, Al composition 0.14, In composition 0.03;
p-type contact layer 117: Mg-doped GaN, growth temperature 900 ° C., thickness 50 nm.

After depositing an insulating film 118 such as a silicon oxide film on the p-type contact layer 117, a stripe window having a width of 10 μm was formed using photolithography and wet etching. A p-electrode (Ni / Au) 119a contacting the p-type contact layer 117 through the stripe window was formed, and a pad electrode (Ti / Au) was deposited. On the back surface of the GaN template 110, an n-electrode (Ni / Al) 119b was formed and a pad electrode (Ti / Au) was deposited. The substrate product produced by these steps was formed with an end face for the resonator at intervals of 800 μm. A reflection film made of a SiO ₂ / TiO ₂ multilayer film was formed on the end face for the resonator to produce a gain guide type laser diode. The laser diode oscillated at 520 nm. The threshold current was 7 kA / cm ² . In addition, when the support body of template S5 does not have electroconductivity, n electrode 103b is provided so that an ohmic contact may be made with the exposed surface of template S5 partially exposed by etching or the like.

  As a preliminary experiment, a GaN wafer was used instead of the GaN template. According to the knowledge of the inventors, the experiment using the GaN wafer can provide the same result as the experiment using the GaN template having the same plane orientation as that of the GaN wafer. A GaN substrate having a {20-21} plane (m plane + 75 degree off GaN substrate) and a GaN substrate having a {20-2-1} plane (m plane—75 degree off GaN substrate) are arranged on the susceptor of the growth reactor. did. At the same time, a semiconductor stack for a light emitting device was grown on these GaN substrates. The active layer has a quantum well structure, the well layer is made of InGaN, and the barrier layer is made of GaN. The growth temperature of the active layer was 800 degrees.

FIG. 22 is a diagram showing a photoluminescence (PL) spectrum PL ₊₇₅ of a quantum well structure on an m-plane ₊ 75-degree off-GaN substrate and a PL spectrum PL- ₇₅ of a quantum well structure on an m-plane-75-degree off-GaN substrate. . The peak wavelength of the PL spectrum PL ₊₇₅ is 424 nm, and the peak wavelength of the PL spectrum PL ₋₇₅ is 455 nm. The peak wavelength difference is about 30 nm. This is because the In incorporation of the {20-2-1} plane inclined from the N plane is larger than the {20-21} plane inclined from the Ga plane. Is shown. With respect to the [000-1] axis selected as the direction of the reference axis Cx shown in FIG. 1, the normal line of the substrate main surface forms an inclination angle in the range of 63 degrees to less than 80 degrees in the m-axis direction. Sometimes, the main surface of the substrate exhibits a good In uptake ability.

Subsequently, the growth of the GaN-based semiconductor will be described.
1. Growth mechanism of GaN and InGaN (stable surface)
The growth mechanism of GaN and InGaN will be described. In the growth of a GaN-based semiconductor, there is a plane orientation such as a c-plane that forms a flat growth surface at the atomic level during crystal growth, for example, this plane orientation is called a “stable plane”. The growth mechanism of GaN on the stable surface is as follows. In GaN growth on a stable surface, the growth surface is formed from macro atomic layer steps having a large terrace width on the order of several 100 nm. The growth mechanism of GaN is classified into three types in terms of the growth temperature.

  FIG. 23 is a drawing schematically showing a growth mode when the growth temperature is high and a growth mode when the growth temperature is low. At the growth temperature exceeding 900 degrees Celsius in the growth furnace, the growth mode shown in FIG. At high growth temperature, the migration of GaN molecules on the growth surface is large, so it is rarely taken into the crystal on the terrace, and the crystal is not crystallized for the first time when the GaN molecule reaches the step edge with a large activation energy called kink. Captured inside. As a result, in the growth, the step end extends in a laminated form. This growth mode is called “step flow growth”. FIG. 24 is a drawing showing an AFM image of the growth surface of GaN. Referring to FIG. 24 (a), it can be clearly seen that atomic layer steps are formed in a certain direction.

  On the other hand, the growth mode shown in FIG. 23B occurs at a growth temperature of about 700 to 900 degrees Celsius in the growth furnace. At low growth temperatures, the migration of molecules at the growth surface is small, so that the molecules do not reach the step edge and are incorporated into the crystal on a large terrace. The part where the molecule is taken in becomes a nucleus and grows so that the step spreads. This growth mode is called “growth on the terrace”. FIG. 24B is a drawing showing an AFM image of the growth surface of GaN grown by growth on the terrace. In this growth morphology, a large number of nuclei are formed, and steps are spread from the large number of nuclei. Therefore, the steps do not extend in one direction but are formed in all directions.

  At a growth temperature of 700 degrees Celsius or lower, a growth mode different from the above growth mode occurs. At very low growth temperatures, there is almost no molecular migration, so GaN molecules are immediately incorporated into the crystal when they reach the growth surface. Therefore, crystal defects are very easily introduced, and it is difficult to grow a high-quality GaN film. This growth mode is called “island growth”.

  Next, growth on crystal planes with various plane orientations inclined in the m-axis direction from the c-plane will be described. GaN was grown at a growth temperature of 1100 degrees Celsius on crystal planes with various plane orientations inclined in the m-axis direction from the c-plane. When the surface was observed by AFM, it was found that the plane orientation in which the macro atomic layer step as shown in FIG. 23A was observed was only the step composed of the following three types of planes. That is, these surfaces are the c-plane, the m-plane, and the {10-11} plane inclined at about 62 degrees from the c-plane. That is, in the growth on the crystal plane in which the c-plane is inclined in the m-axis direction, only the above three planes can be regarded as stable planes. Surfaces other than the three types of stable surfaces are collectively referred to as “unstable surfaces”.

  Next, the growth mechanism of InGaN on the stable surface will be described. The growth mechanism of InGaN is considered to be basically the same as that of GaN. The difference is that in InGaN growth, the residence time of InN on the growth surface is shorter than that of GaN, and InN desorption occurs easily. Therefore, when it is desired to add In having a certain size of In to the crystal, it is necessary to lower the growth temperature, and the temperature is approximately 900 degrees Celsius or less. That is, the growth of InGaN on the stable surface becomes growth on the terrace.

2. Growth mechanism of GaN and InGaN (unstable surface)
The growth mechanism of GaN and InGaN on the non-stable surface will be described. According to AFM observation of the GaN surface grown on the surface of the non-stable surface at the growth temperature of 1100 degrees Celsius, in the growth on the plane orientation of the relatively small inclination angle (referred to as “sub-off angle”) from the stable surface. Fine steps formed from a stable surface close to the off angle were observed. The terrace width is smaller than the growth of the stable plane just to the plane orientation, and becomes smaller as the sub-off angle increases. When the tilt was about 2 degrees with respect to the stable surface, the atomic layer step was not observed in the AFM image. From these results, a stable surface is likely to appear during growth near the stable surface, and a step having a relatively large terrace width is formed. FIG. 25A is a drawing schematically showing a growth mechanism of step flow growth in high-temperature growth of GaN and InGaN on an unstable surface. In FIG. 25, the arrow indicates the growth direction.

  On the other hand, when it is greatly inclined from the stable surface, the terrace width is reduced, and it is considered that micro steps that cannot be observed in the AFM image are formed. In addition, since there are only three types of stable surfaces, this micro step is also formed by a micro terrace composed of stable surfaces, and the growth of the step extends in a certain direction on the surface of GaN grown at high temperature. it seems to do.

  The growth mechanism of GaN when the growth temperature is low will be described. In the vicinity of the stable surface, a wide terrace composed of the stable surface is likely to be formed, and the migration of molecules on the growth surface is small, so the growth on the terrace is dominant. FIG. 25B is a drawing schematically showing a growth mechanism of growth on a terrace in low-temperature growth of GaN and InGaN on an unstable surface.

  On the other hand, in the growth from a stable surface to a crystal plane having a large sub-off angle, the step density of the surface is increased, and the terrace width becomes as small as several nanometers. When the sub-off angle from the stable surface is large, the growth mechanism of growth on the terrace hardly occurs because of the narrow terrace width. Even at a growth temperature where the migration of molecules on the growth surface is small, atoms easily reach the step end where the activation energy is high. That is, when the sub-off angle from the stable surface becomes large, it can be considered that the step end grows to a lower temperature. This growth is referred to herein as “step edge growth” because the scale of the terrace width is nearly two orders of magnitude smaller than the step flow growth. FIG. 25C is a drawing schematically showing the growth mechanism of step edge growth in the low temperature growth of GaN and InGaN on the unstable surface.

  From the above description, it can be considered as follows. When the growth temperature is low, growth on the terrace is dominant in the stable surface and in the vicinity of the stable surface. As the sub-off angle from the stable surface increases, the growth on the terrace gradually weakens, and the step edge growth becomes dominant. This also coincides with the growth mechanism of InGaN having a low growth temperature.

3. Regarding In incorporation, In incorporation on each growth surface in InGaN growth will be described. In order to investigate the In composition, an experiment was conducted to grow InGaN under the same conditions at 760 degrees Celsius on a GaN substrate inclined at various inclination angles in the m-axis direction from the c-plane. FIG. 26 shows the experimental results, in which the horizontal axis indicates the inclination angle (off angle) from the c-axis to the m-axis direction, and the vertical axis indicates the In composition of the grown InGaN.
Angle In composition
0 21.6
10 11.2
16.6 9.36
25.9 7.54
35 4.33
43 4.34
62 22.7
68 29
75 19.6
78 18.5
90 23.1
The unit of the angle is “degree”.
Referring to FIG. 26, the In incorporation at the c-plane is good. As the off angle is increased from the c-plane, the incorporation of In decreases. As the off-angle is further increased, In incorporation begins to improve around the inclination angle exceeding 40 degrees. In incorporation of the {10-11} plane, which is a stable plane, is about the same as that of the c plane. As the off-angle is further increased, the In uptake is improved and shows a local maximum at around 68 degrees. When this angle is exceeded, In uptake decreases. In incorporation shows a local minimum around an off angle of 80 degrees. In incorporation is improved when approaching the m-plane beyond this angle. The m plane shows the same amount of In uptake as the c plane.

  The behavior of In incorporation will be described based on the growth mechanism of InGaN in items 1 and 2.

  First, as shown in FIG. 23B, when the growth on the terrace is dominant in the vicinity of the stable surface, In is well taken in as shown in FIG. The reason why In incorporation is good on a terrace composed of stable surfaces can be explained from the atomic arrangement on the crystal surface as follows. FIG. 27 shows a surface atomic arrangement of (10-11) plane as an example. Referring to FIG. 27, c-plane c0 and (10-11) plane are shown. As shown in FIG. 27, the In atom is bonded to two N atoms indicated by an arrow Y (In) with two bonds. Two N atoms are arranged in the X-axis direction in the orthogonal coordinate system T in FIG. These two N atoms can be displaced in the positive (front) direction and the negative (depth) direction of the X axis in the Cartesian coordinate system T in FIG. 27, and this arrangement is in a state where In atoms having a large atomic radius are likely to be taken in. . This atomic arrangement is considered to indicate the reason why In is easily taken in by growth on the terrace.

  In incorporation in the case of step edge growth based on the same concept will be described. FIG. 28 shows an atomic arrangement on the growth surface of a plane inclined by about 45 degrees in the m-axis direction as an example. Referring to FIG. 28, c-plane c0, a 45-degree inclined plane m45 and a (10-11) plane from the c-plane are shown. Focusing on the step end, the In atom is bonded to two N atoms indicated by the arrow B1 (In) with two bonds, and is different from one N atom indicated by the arrow R (In). Join with one bond. In this case, the N atom indicated by the arrow B1 (In) related to the bond with the In atom is perpendicular to the direction in which the N atom indicated by the arrow R (In) can be displaced, and In having a large atomic radius is taken in. In order to achieve this, it is necessary to displace three N atoms, and this atomic arrangement is in a state where it is difficult to incorporate In. Therefore, it is considered that In incorporation is poor in step edge growth. When these are considered together, a part of the result of FIG. 26 can be well explained. That is, in the plane orientation between the c-plane and the {10-11} plane, growth on the terrace is dominant in the vicinity of the stable plane, and In incorporation is good. On the other hand, as the sub-off angle from the stable surface increases, the growth on the terrace weakens and the step edge growth becomes dominant, so that the In incorporation becomes smaller.

  On the other hand, it is considered that the same idea holds between the {10-11} plane and the m plane.

  However, in the range where the off angle from the c-plane closer to the {10-11} plane between the {10-11} plane and the m-plane is 63 degrees or more and less than 80 degrees, the above explanation cannot be understood. It shows behavior. Therefore, when further examining the surface atomic arrangement in this angular range, it was found that In is well incorporated at the step end only in this angular range. FIG. 29 schematically shows, as an example, the state of the step on the surface of the c-plane inclined at an off angle of 75 degrees in the m-axis direction. In the above angle range, as shown in FIG. 29, the growth surface is composed of micro steps formed from the (10-11) plane and the m plane. The step end grows so that the step end extends in the m-axis direction. FIG. 30 shows an atomic arrangement on the growth surface of a plane inclined by about 75 degrees in the m-axis direction as an example. Referring to FIG. 30, an m-plane m0, a 75-degree inclined plane m75 and a (10-11) plane from the c-plane are shown. In this case, one N atom indicated by arrow R2 (In) is bonded by one bond, and one N atom indicated by arrow B2 (In) is bonded by one bond. In this arrangement, the direction in which two N atoms can be displaced is in opposition, and only two N atoms need to be displaced in order to incorporate In having a large atomic radius. It can be considered that In atoms are easily incorporated. In addition, the surface atom arrangement of step edges in other angle ranges was also examined. The inventors have found that the angle at which the growth at the step end showing good In incorporation is possible is only in the above range.

  Based on the above consideration, the off-angle dependence of In incorporation was estimated. FIG. 31 is a diagram showing the relationship between In incorporation and off-angle. The In incorporation estimates both the growth component on the terrace and the step edge growth component, and the total In incorporation is represented by the sum of these. On the vertical axis, the In uptake is normalized to In uptake on the c-plane. The solid line T indicates the amount of In taken in by growth on the terrace, the solid line S shows the amount of In taken in by step edge growth, and the solid line SUM shows the sum. As described above, in the growth on the terrace, the In incorporation is high in the vicinity of the stable surface where the growth on the terrace is dominant, and the growth on the terrace is not dominant and the In is not taken in as the distance from the stable surface increases.

  On the other hand, the step edge growth becomes dominant as the step density increases as the distance from the stable surface increases. However, there is almost no In incorporation due to step edge growth outside the angle range from the c-plane with an inclination angle of 63 ° to less than 80 °. A large In uptake occurs at the step end only in an angle range of an inclination angle of 63 degrees or more and less than 80 degrees, and therefore the behavior is such that the In uptake increases as the step end growth becomes active. As a result, the off-angle dependence as shown by the solid line SUM is obtained, and the estimation shown in FIG. 31 well explains the experimental result shown in FIG.

4). Based on the above results regarding In segregation, In segregation in the InGaN film will be described. In an optical element having an InGaN active layer on a c-plane substrate, In segregation in the InGaN crystal increases as the emission wavelength of the active layer becomes longer, that is, as the In composition in the InGaN crystal increases. As a result, the crystal quality of InGaN deteriorates, and a decrease in emission intensity and an increase in the half-value width of the emission wavelength are observed. On the other hand, according to the experiments by the inventors, in the range where the inclination angle of the c-axis in the m-axis direction is not less than 63 degrees and less than 80 degrees, the decrease in emission intensity of the InGaN layer that emits light in the long wavelength region It is smaller than the InGaN layer on the stable surface, and the increase in half width is small.

  The inventors examined this reason based on the growth mechanism and In incorporation. The reason why the InGaN film grown on the stable surface exhibits large In segregation is considered as follows. As shown in FIG. 23B, in the In incorporation in the growth on the terrace, the GaN and InN molecules migrate on the wide terrace after reaching the terrace and before being incorporated into the crystal. During the migration, InN spontaneously aggregates due to the immiscibility of GaN and InN. This aggregation is thought to cause In segregation in the InGaN crystal.

  On the other hand, as shown in FIG. 31, when the sub-off angle from the stable surface is large, In is taken in at the step end. The GaN and InN molecules that have reached the growth surface hardly migrate on the narrow terrace and are immediately taken into the crystal. Therefore, it is considered that the incorporated In is distributed almost randomly in the InGaN crystal and the In segregation is small. This tendency is considered to be more remarkable as the step density is larger. For this reason, a uniform InGaN film is obtained as the sub-off angle from the stable surface increases. However, as described above, in the step edge growth, the In incorporation is poor at an inclination angle excluding a specific angle range. Therefore, in order to obtain a desired In composition, it is necessary to lower the growth temperature. As the growth temperature decreases, the dominant growth mode changes from step edge growth to island growth. As a result, crystal defects and the like increase and the quality of the InGaN film significantly deteriorates.

  As described above, it is considered that In incorporation and In segregation are in a trade-off relationship. The inventors have found a range in which In incorporation and In segregation are compatible. This angle range is an inclination angle of 63 degrees or more and less than 80 degrees in the m-axis direction from the c-axis. In this angular range, In is efficiently taken in even by step edge growth, and In segregation in the InGaN film is small. In particular, in the angle range of 70 degrees or more and less than 80 degrees, the step density increases, so that an InGaN film with smaller In segregation and higher homogeneity can be grown. Further, when In incorporation is taken into consideration, the step edge growth and the growth on the terrace are well balanced particularly in an angle range of 71 degrees or more and 79 degrees or less. Among them, the balance between step edge growth and growth on the terrace is the best at an angle of 72 degrees to 78 degrees. Therefore, it is possible to raise the growth temperature of the InGaN film in order to obtain a desired composition, and it is possible to grow a uniform InGaN film with few crystal defects.

  32 and 33 are drawings showing the characteristics of each surface and angle range in terms of the above-described In uptake, In segregation, and piezoelectric field. In FIGS. 32 and 33, the double circle symbol shows particularly good characteristics, the single circle symbol shows good characteristics, the triangle symbol shows particularly normal characteristics, and the cross symbol shows inferior characteristics. . As characteristic angles, inclination angles from the c-axis to the m-axis are 63 degrees, 70 degrees, 71 degrees, 72 degrees, 78 degrees, 79 degrees, and 80 degrees. An angle range of 63 degrees or more and less than 80 degrees in the m direction, in particular, an angle range of 70 degrees or more and less than 80 degrees, further 71 degrees or more and 79 degrees or less, of which an angular range of 72 degrees or more and 78 degrees or less is a long wavelength In producing an optical element in a region, particularly a light-emitting diode element or a laser diode element, it is very advantageous because of its low luminous efficiency and low half-width of light emission.

  In the above description, for example, a notation such as a plane orientation (20-21) or (10-11) is used. When considering the description of this embodiment, those skilled in the art think that the effects of the invention described in this embodiment can be obtained in terms of crystallographic equivalents. Therefore, for example, the plane orientation “(20-21)” is equivalent to (2-201), (−2201), (20-21), (−2021), (02-21), (0-221). Can be considered to be included.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

  In recent years, long-wavelength light emission is desired in GaN-based light-emitting elements, and a semipolar plane with an inclination angle from the c-plane and nonpolar planes typified by the m-plane and a-plane are attracting attention. The reason is as follows. Since the In composition of the well layer increases in order to obtain long-wavelength light emission, the lattice constant difference between the well layer and the barrier layer increases, and a large distortion occurs in the light-emitting layer. At this time, on the polar surface such as the c-plane, the quantum efficiency of the light-emitting element decreases due to the action of the piezoelectric field. In order to avoid this, studies on various crystal planes such as non-polar planes (a-plane and m-plane) are underway. However, the current situation is that nothing exceeding the efficiency on the c-plane has been made. In order to form a microstep structure in which the principal surface of the substrate is a {10-11} plane inclined at an angle of about 62 degrees in the m-axis direction from the c plane and the m plane, Attention was paid to the surface inclined at an angle of 63 degrees or more and less than 80 degrees in the m-axis direction. In particular, the {20-21} plane, which is an inclined plane of 75 degrees in the m-axis direction from the c-plane, and an inclination angle of 63 degrees from the c-plane around the plane in the m-axis direction, or more than 70 degrees and less than 80 degrees. Focused on the area. In this region, the width of the terrace composed of {10-11} plane and the width of the terrace composed of m-plane are small on the main surface of the substrate, the step density is large, and In segregation is small.

11a, 11b: GaN-based semiconductor optical device, VN: normal vector, VC + ... [0001] axial vector, VC -... [000-1] axial vector, Sc ... plane, Cx ... reference axis, Ax ... Predetermined axis, 13 ... template, 13a ... main surface of template, 15 ... GaN-based semiconductor epitaxial region, 17 ... active layer, α ... main surface inclination angle, 19 ... semiconductor epitaxial layer, M1, M2, M3 ... surface morphology, 21 ... GaN-based semiconductor region, 23 ... n-type GaN semiconductor layer, 25 ... n-type InGaN semiconductor layer, 27 ... electron blocking layer, 29 ... contact layer, 31 ... quantum well structure, 33 ... well layer, 35 ... barrier layer, 37 ... first electrode, 39 ... second electrode, A _OFF ... off angle in the a-axis direction, 41 ... n-type cladding layer, 43a ... light guide layer, 43b ... light guide layer, 45 ... electricity Sub block layer, 47 ... cladding layer, 49 ... contact layer, 51 ... first electrode, 53 ... insulating film, 55 ... second electrode, 131 ... support, 131a ... support main surface, 133 ... mask, 133a ... Opening, 135a ... concave, 133b ... stripe, 135a, 135b ... side surface, 137 ... insulator, 139 ... semiconductor region, 139a ... main surface of semiconductor region, 141 ... foreign substrate, 141a ... main surface of different substrate, 143 ... Mask, 143a ... stripe, 143b ... opening, 145 ... support, 145a ... main surface of support, 147 ... recess, 147a, 147b ... side of recess, 149 ... insulating film, 151 ... semiconductor region

Claims (25)

A gallium nitride based semiconductor optical device,
A support having a main surface made of a material different from that of the gallium nitride semiconductor; a mask having an opening and covering the main surface; and first and second side surfaces provided on the support in the opening of the mask. A template including a recess, an insulator covering the second side surface, and a semiconductor region provided on the first and second side surfaces and embedding the mask;
A gallium nitride based semiconductor epitaxial region provided on the template;
A semiconductor epitaxial layer provided on the gallium nitride based semiconductor epitaxial region for an active layer ;
With
The semiconductor region is made of a first gallium nitride based semiconductor, and the c-axis direction of the first gallium nitride based semiconductor is defined by the plane orientation of the first side surface,
The main surface of the semiconductor region of the template is 63 degrees or more in the direction of the m-axis of the first gallium nitride semiconductor from the plane orthogonal to the reference axis extending along the c-axis of the first gallium nitride semiconductor. Inclined at an inclination angle of less than 80 degrees,
The first side surface is inclined relative to the main surface of the support, intersection angles between the main surface and the first side of the support is in the range of less than 80 degrees 63 degrees Yes,
The second side surface is inclined with respect to the main surface of the support;
The semiconductor epitaxial layer is made of a second gallium nitride based semiconductor containing indium as a constituent element,
The c-axis of the second gallium nitride semiconductor is inclined with respect to the normal axis of the main surface of the semiconductor region;
The direction of the reference axis is the direction of either the [0001] axis or the [000-1] axis of the first gallium nitride semiconductor.   2. The main surface of the semiconductor region is inclined at an angle of 70 degrees or more from a plane perpendicular to the reference axis in the m-axis direction of the first gallium nitride semiconductor. The gallium nitride based semiconductor optical device described in 1.   The main surface of the semiconductor region is inclined at an angle of 71 degrees or more and 79 degrees or less from a plane perpendicular to the reference axis in the m-axis direction of the first gallium nitride semiconductor. A gallium nitride based semiconductor optical device according to claim 1 or 2.   The off angle in the a-axis direction of the first gallium nitride semiconductor is a finite value and is in a range of not less than -3 degrees and not more than +3 degrees. 2. A gallium nitride based semiconductor optical device according to one item. A second conductivity type gallium nitride based semiconductor layer provided on the active layer;
The gallium nitride based semiconductor epitaxial region includes a first conductivity type gallium nitride based semiconductor layer,
The active layer includes well layers and barrier layers alternately arranged in a predetermined axis direction,
The well layer is made of the semiconductor epitaxial layer, the barrier layer is made of a gallium nitride based semiconductor, the semiconductor epitaxial layer is made of InGaN containing strain,
The first conductivity type gallium nitride based semiconductor layer, the active layer, and the second conductivity type gallium nitride based semiconductor layer are arranged in the direction of the predetermined axis, and the direction of the reference axis is the direction of the predetermined axis The gallium nitride based semiconductor optical device according to claim 1, wherein the gallium nitride based semiconductor optical device is different from a direction.   The gallium nitride based semiconductor light according to any one of claims 1 to 5, wherein the active layer is provided so as to generate light in a wavelength range of 370 nm or more and 650 nm or less. element.   The gallium nitride based semiconductor light according to any one of claims 1 to 6, wherein the active layer is provided so as to generate light having a wavelength range of 450 nm to 600 nm. element.   The main surface of the semiconductor region is inclined at an angle in a range of −3 degrees to +3 degrees from either the {20-21} plane or the {20-2-1} plane of the first gallium nitride semiconductor. The gallium nitride based semiconductor optical device according to claim 1, wherein the gallium nitride based semiconductor optical device is a semiconductor surface.   The gallium nitride based semiconductor optical device according to any one of claims 1 to 8, wherein the reference axis is oriented in the direction of the [0001] axis.   The gallium nitride based semiconductor optical device according to any one of claims 1 to 9, wherein the reference axis is oriented in the direction of the [000-1] axis.   The gallium nitride based semiconductor optical device according to any one of claims 1 to 10, wherein the semiconductor region is made of GaN. The surface morphology of the main surface of the semiconductor region has a plurality of microsteps,
12. The gallium nitride based semiconductor optical device according to claim 1, wherein main constituent surfaces of the microstep include at least an m-plane and a {10-11} plane. .   The gallium nitride based semiconductor according to any one of claims 1 to 12, wherein the support is made of any one of spinel, sapphire, zinc oxide, silicon carbide, silicon, and gallium oxide. Optical element.   14. The semiconductor region according to claim 1, wherein the semiconductor region includes a semiconductor epitaxially grown in the c-axis direction of the first gallium nitride based semiconductor on the first side surface of the recess. A gallium nitride based semiconductor optical device according to any one of the above. A method of fabricating a gallium nitride based semiconductor optical device,
A support having a main surface made of a material different from that of a gallium nitride semiconductor, a mask having an opening and covering the main surface, and first and second side surfaces provided on the main surface in the opening of the mask Preparing a template including a recess, an insulator covering the second side surface, and a semiconductor region provided on the first and second side surfaces and embedding the mask;
Growing a gallium nitride based semiconductor epitaxial region on the main surface of the template;
Forming a semiconductor epitaxial layer for an active layer on a main surface of the gallium nitride based semiconductor epitaxial region ;
With
The semiconductor region is made of a first gallium nitride based semiconductor,
The main surface of the semiconductor region of the template is 63 degrees or more in the direction of the m-axis of the first gallium nitride semiconductor from the plane orthogonal to the reference axis extending along the c-axis of the first gallium nitride semiconductor. Inclined at an inclination angle of less than 80 degrees,
The crossing angle between the main surface of the support and the first side surface is in a range of not less than 63 degrees and less than 80 degrees, and the first side surface is inclined with respect to the main surface of the support,
The second aspect, Ri Contact inclined with respect to the main surface of said support,
C-axis of the second gallium nitride semiconductor is inclined with respect to the normal axis of said main surface of said semiconductor region,
The semiconductor epitaxial layer is made of a second gallium nitride based semiconductor, and the second gallium nitride based semiconductor contains indium as a constituent element,
The c-axis of the second gallium nitride based semiconductor is inclined with respect to the reference axis;
The reference axis is directed to either the [0001] axis or the [000-1] axis of the first gallium nitride based semiconductor.   The main surface of the semiconductor region is inclined at an angle in a range of 70 degrees or more from a plane perpendicular to the reference axis in the m-axis direction of the first gallium nitride semiconductor. Item 16. The method according to Item 15.   The main surface of the semiconductor region is inclined at an angle of 71 degrees or more and 79 degrees or less from a plane perpendicular to the reference axis in the m-axis direction of the first gallium nitride semiconductor. 17. A method as claimed in claim 15 or claim 16. The active layer has a quantum well structure including well layers and barrier layers alternately arranged in a predetermined axis direction;
The well layer comprises the semiconductor epitaxial layer;
The barrier layer is made of a gallium nitride based semiconductor,
The method is
Forming the barrier layer on the semiconductor epitaxial layer;
On the active layer, and growing a second conductivity type gallium nitride based semiconductor layer,
With
The gallium nitride based semiconductor epitaxial region includes a first conductivity type gallium nitride based semiconductor layer,
The first conductivity type gallium nitride based semiconductor layer, the active layer, and the second conductivity type gallium nitride based semiconductor layer are arranged in a predetermined axis direction, and the direction of the reference axis is the direction of the predetermined axis The method according to any one of claims 15 to 17, characterized in that   The off angle in the a-axis direction of the first gallium nitride semiconductor is a finite value and is in a range of not less than -3 degrees and not more than +3 degrees. The method according to one item.   The inclination angle of the main surface of the semiconductor region is −3 degrees or more and +3 degrees from the crystal plane of the {20-21} plane or {20-2-1} plane of the first gallium nitride semiconductor. The method according to claim 15, wherein the method is distributed in the following range. The semiconductor region of _{In S Al T Ga 1-S} -T N (0 ≦ S ≦ 1,0 ≦ T ≦ 1,0 ≦ S + T <1) made of, claim 15 claim 20, characterized in that The method as described in any one.   The method according to any one of claims 15 to 21, wherein the semiconductor region is made of GaN. The surface morphology of the main surface of the semiconductor region has a plurality of microsteps,
The method according to any one of claims 15 to 22, wherein the main constituent surfaces of the microstep include at least an m-plane and a {10-11} plane.   The method according to any one of claims 15 to 23, wherein the support is made of any one of spinel, sapphire, zinc oxide, silicon carbide, silicon, and gallium oxide.   The semiconductor region includes a semiconductor epitaxially grown in the c-axis direction of the first gallium nitride based semiconductor selectively on the first side surface of the recess with respect to the second side surface. The method according to any one of claims 15 to 24.