JP2009224602A - Nitride semiconductor laser, method of manufacturing nitride semiconductor laser, and epitaxial wafer for nitride semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser which has cleavage surfaces of good quality. <P>SOLUTION: A semiconductor lamination 15 is provided on a support base 13. The tilt angle of a principal surface 13a of the support base 13 is 20 to 40° in a predetermined direction from a (c) plane of a hexagonal nitride semiconductor. An alternate long and short dash line 13c shows a representative (c) plane of the hexagonal nitride semiconductor of the support base 13. The semiconductor lamination 15 includes a plurality of semiconductor films for a semiconductor laser. An active layer 23 of the semiconductor lamination 15 has a gallium nitride-based semiconductor layer containing indium, and an indium composition of the gallium nitride-based semiconductor layer is ≥0.2. An upper surface 15a of the semiconductor lamination 15 has a plurality of projections 19a extending along an X axis, and the plurality of projections 19a are arrayed in a direction of, for example, a Y axis. The semiconductor lamination 15 has first and second cleavage surfaces 17a and 17b extending in a second direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor laser, a method of manufacturing a nitride semiconductor laser, and an epitaxial wafer for the nitride semiconductor laser.

  Patent Document 1 describes a semiconductor light emitting element. The semiconductor light-emitting element has a semiconductor layer that reduces the threshold current density necessary for laser oscillation and is less susceptible to cracking. In addition, in a surface-emitting semiconductor laser, the vibration surface of light is fixed and fluctuation of the vibration surface is suppressed.

  Patent Document 2 describes a semiconductor laser using a nitride III-V compound semiconductor. A nitride III-V compound semiconductor layer forming a laser structure is epitaxially grown on a GaN substrate. The GaN substrate is made of a nitride III-V group compound semiconductor having a wurtzite crystal structure, and its main surface is a plane substantially perpendicular to the {0001} plane, for example, {01-10} plane, {11-20 } The plane or these planes are off within -5 degrees to +5 degrees. The GaN substrate is cleaved along with the nitride-based III-V compound semiconductor layer thereon along the {0001} plane, which is an easy cleavage plane, to form a resonator end face.

  Patent Document 3 describes a light-emitting diode element, a semiconductor laser element, a light-receiving element, and a transistor manufactured from a group III nitride semiconductor. In these group III nitride semiconductors, an AlGaN layer having a large Al composition and a high carrier concentration is required. In the growth of the AlGaN layer, although the surface diffusion of Al atoms is small, the surface diffusion of Al atoms is promoted. An AlGaN layer having a large Al composition and a high carrier concentration can be grown on a substrate having a GaN inclined surface of 1 to 20 degrees without impairing the crystal quality.

  Non-Patent Document 1 describes an InGaN light emitting diode. This light emitting diode is fabricated on a semipolar (11-22) plane (off angle of 56 degrees in the a-axis direction from the c-plane) GaN substrate. The light emitting diode has a single quantum well structure composed of an InGaN well layer having a width of 3 nm. The following characteristics were obtained: blue (wavelength 430 nm), light output 1.76 mW, external quantum efficiency 3.0%. It was green (wavelength 530 nm), the light output was 1.91 mW, and the external quantum efficiency was 4.1%. The optical output was 0.54 mW at amber (wavelength 580 nm), and the external quantum efficiency was 1.3%. The emitted light was confirmed to be polarized in the [1-100] direction.

Non-Patent Document 2 and Non-Patent Document 3 describe InGaN-based light emitting diodes that generate green light.
Japanese Patent Laid-Open No. 10-135576 JP-A-10-335750 JP 2002-16000 A Japanese Journal of Applied Physics Vol.45, No. 26, 2006, pp. L659-L662 Jpn. J. Appl. Phys. 45 (2006) 9001 Jpn. J. Appl. Phys. 36 (1997) L382

  As shown in the above-mentioned patent documents and non-patent documents, a light emitting element is fabricated on a GaN substrate having not only the c-plane but also the m-plane and a-plane and further a semipolar plane.

  Patent Documents 1 and 2 describe semiconductor lasers using nonpolar surfaces. In Patent Document 3, a light emitting device is fabricated using an active layer having a small indium composition on a GaN surface inclined from the c-plane. However, in a semiconductor laser using a semipolar plane, an active layer having a large indium composition is used. Non-Patent Documents 1 to 3 describe light-emitting diodes and do not mention semiconductor lasers.

  A semiconductor laser using a semipolar plane has a smaller piezo electric field than a semiconductor laser using a c-plane, so that an active layer having a relatively large indium composition can increase luminous efficiency and is advantageous for longer wavelengths.

  In the production of a semiconductor laser, the crystal quality of the epitaxial layer is important, but the oscillation characteristics are greatly influenced not only by this crystal quality but also by the quality of the end face for the Fabry-Perot resonator. When fabricating a semiconductor laser on a semipolar plane, the end face for a Fabry-Perot resonator is fabricated by cleavage. Therefore, in the production of a semiconductor laser using a semipolar plane, it is necessary to consider the cleaved crystal plane.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a nitride semiconductor laser having a cleaved surface of good quality, and a method for manufacturing the nitride semiconductor laser. It is another object of the present invention to provide an epitaxial wafer for the nitride semiconductor laser.

  According to one aspect of the present invention, a nitride semiconductor laser comprises (a) a hexagonal nitride semiconductor, and has a main surface and a back surface that are inclined in a predetermined direction from the c-plane of the hexagonal nitride semiconductor. A support base; and (b) a first conductivity type nitride semiconductor layer, a second conductivity type nitride semiconductor layer, and an active layer, provided on the main surface of the support base, for a semiconductor laser. A semiconductor stack. The surface morphology of the semiconductor stack has a plurality of protrusions extending in a first direction, and the semiconductor stack includes first and second cleavage planes extending in a second direction intersecting the first direction. The inclination angle of the main surface of the support base is 20 degrees or more, the inclination angle is 40 degrees or less, and the active layer includes a gallium nitride based semiconductor layer containing indium. The gallium nitride based semiconductor layer has an indium composition of 0.2 or more, and the active layer is provided between the first conductivity type nitride semiconductor layer and the second conductivity type nitride semiconductor layer. .

  According to this nitride semiconductor laser, a semiconductor layer having a high indium composition of 0.2 or more is included in the active layer. The surface morphology of the semiconductor stack has a plurality of protrusions extending in the first direction. For this reason, the first and second cleavage planes of the semiconductor stack are formed so as to extend in the second direction intersecting the first direction, so that the quality of the cleavage plane is good and the cleavage plane is also good. The yield is good.

  In the nitride semiconductor laser of the present invention, the predetermined direction is preferably in an angle range of −0.1 degrees or less +0.1 degrees or more from the <11-20> direction. According to this nitride semiconductor laser, when the direction in which the c-axis of the support base is inclined is slightly shifted with respect to the a-axis of the support base, the semiconductor laminated layer including a semiconductor layer having a high indium composition of 0.2 or more In the surface morphology, the regularity of the arrangement of the protrusions becomes high.

  In the nitride semiconductor laser according to the aspect of the invention, it is preferable that the predetermined direction is an angle range of not less than −0.1 degrees and not more than +1 degree from the <11-20> direction. According to this nitride semiconductor laser, it is possible to avoid a decrease in gain due to the shaking in the extending direction of the laser cavity.

In the nitride semiconductor laser of the present invention, the support base has a gallium nitride based semiconductor region having a threading dislocation density of 1 × 10 ⁷ cm ⁻² or less, and the first conductivity type nitride semiconductor layer, the active layer In addition, the second conductivity type nitride semiconductor layer may be located on the gallium nitride based semiconductor region. According to this nitride semiconductor laser, since the first conductivity type nitride semiconductor layer, the active layer, and the second conductivity type nitride semiconductor layer are grown on the low dislocation region, the influence of dislocation on the surface morphology of the semiconductor stack is affected. Reduced to reveal features from semipolar planes and high indium compositions.

  In the nitride semiconductor laser of the present invention, the support base is made of GaN, and the support base is a first region having a threading dislocation density smaller than the first threading dislocation density, and larger than the first threading dislocation density. A first region having a threading dislocation density, and the first region may extend in a direction perpendicular to the predetermined direction and a c-axis direction of the hexagonal nitride semiconductor. According to this nitride semiconductor laser, a semiconductor laser can be fabricated in a low dislocation region of a large-diameter GaN wafer.

  In the nitride semiconductor laser of the present invention, the first and second cleavage planes are preferably m-planes. According to this nitride semiconductor laser, the m-plane is easy to cleave.

  The nitride semiconductor laser of the present invention can further include an electrode extending in the direction from the first cleavage plane to the second cleavage plane and provided on the surface of the semiconductor stack. According to this nitride semiconductor laser, the electrodes are provided along the laser cavity including the first cleaved surface and the second cleaved surface, and a semiconductor laser with good characteristics is provided.

  Another aspect of the present invention is a method for fabricating a nitride semiconductor laser. This method includes (a) preparing a wafer made of a hexagonal nitride semiconductor having a main surface and a back surface inclined in a predetermined direction from the c-plane of the hexagonal nitride semiconductor, and (b) A step of growing a one-conductivity-type nitride semiconductor layer on the wafer; and (c) a gallium nitride-based semiconductor layer for an active layer of the nitride semiconductor laser after the first-conductivity-type nitride semiconductor layer is grown And (d) after forming the active layer, growing a second conductivity type nitride semiconductor layer on the wafer to form an epitaxial wafer including a semiconductor stack; (E) forming an electrode after forming the epitaxial wafer to produce a substrate product; and (f) forming a cleavage plane by cleaving the substrate product after forming the electrode. Can be preparedThe surface morphology of the epitaxial wafer has a plurality of protrusions extending in a first direction intersecting the c-axis of the hexagonal nitride semiconductor, and the hexagonal nitride semiconductor of the wafer A cleaved crystal plane extending in a second direction intersecting the first direction, the cleavage plane of the epitaxial wafer extending in a second direction intersecting the first direction, and the wafer The tilt angle of the main surface is 20 degrees or more, the tilt angle is 40 degrees or less, the gallium nitride based semiconductor layer is made of a semiconductor containing indium, and the indium composition of the gallium nitride based semiconductor layer is 0 .2 or more.

  According to this method, a semiconductor layer having an indium composition of 0.2 or more is grown on the semipolar plane. For this reason, the surface morphology of the semiconductor stack has a plurality of protrusions extending in the first direction. Since the epitaxial wafer is cleaved in the second direction intersecting the first direction, the cleavage yield is good and the quality of the cleavage plane is also good.

  In the method of the present invention, the maximum value of the distance between two points on the edge of the wafer is preferably 45 mm or more. According to this method, a large-diameter wafer can be used.

  In the method of the present invention, the predetermined direction is preferably in an angle range of −1 to −0.1 degrees and +0.1 to +1 degrees from the <11-20> direction. According to this method, when the direction in which the c-axis of the wafer is tilted is slightly shifted with respect to the a-axis of the wafer, the protrusion in the surface morphology of the semiconductor stack including the semiconductor layer having a high indium composition of 0.2 or more The regularity of the arrangement of becomes high.

In the method of the present invention, the wafer preferably has a gallium nitride based semiconductor region having a threading dislocation density of 1 × 10 ⁷ cm ⁻² or less. According to this method, since the influence of dislocation is reduced on the surface morphology of the semiconductor stack grown on the low dislocation region, the characteristics derived from the semipolar plane and the high indium composition become clear.

  In the method of the present invention, the wafer includes a first region having a threading dislocation density smaller than a first threading dislocation density, and a second region having a threading dislocation density larger than the first threading dislocation density. The first region may extend in a direction orthogonal to the predetermined direction and a c-axis direction of the hexagonal nitride semiconductor. According to this method, a semiconductor laser can be manufactured in a low dislocation region of a large-diameter GaN wafer.

  In the method of the present invention, the cleavage plane is preferably an m-plane. According to this method, the m-plane is easy to cleave.

  Yet another aspect of the present invention is an epitaxial wafer for a nitride semiconductor laser. The epitaxial wafer includes (a) a hexagonal nitride semiconductor, a wafer having a main surface and a back surface inclined in a predetermined direction from the c-plane of the hexagonal nitride semiconductor, and (b) a first conductivity type. The semiconductor device includes a nitride semiconductor layer, a second conductivity type nitride semiconductor layer, and an active layer, and a semiconductor stack provided on the wafer. The surface morphology of the semiconductor stack has a plurality of protrusions extending in a first direction, and the hexagonal nitride semiconductor of the wafer is cleaved in a second direction intersecting the first direction. The main surface of the wafer has an inclination angle of 20 degrees or more, the inclination angle is 40 degrees or less, and the active layer is a gallium nitride based semiconductor layer containing indium. The gallium nitride based semiconductor layer has an indium composition of 0.2 or more, and the active layer is provided between the first conductivity type nitride semiconductor layer and the second conductivity type nitride semiconductor layer. It has been.

  According to this epitaxial wafer, a semiconductor layer having a high indium composition of 0.2 or more is included in the active layer. For this reason, the surface morphology of the semiconductor stack has a plurality of protrusions extending in the first direction. Since the crystallizable crystal plane of the epitaxial wafer extends in the second direction crossing the first direction, an epitaxial wafer having a good cleavage yield is provided.

  In the epitaxial wafer of the present invention, the maximum value of the distance between two points on the edge of the wafer is preferably 45 mm or more. According to this epitaxial wafer, a large-diameter epitaxial wafer using a large-diameter wafer can be produced.

  In the epitaxial wafer of the present invention, the predetermined direction is preferably in the angle range of −1 to −0.1 degrees and +0.1 to +1 degrees from the <11-20> direction. According to this epitaxial wafer, when the direction in which the c-axis of the wafer is inclined is slightly shifted with reference to the a-axis of the wafer, in the surface morphology of the semiconductor stack including a semiconductor layer having a high indium composition of 0.2 or more, The regularity of the arrangement of the protrusions becomes high.

In the epitaxial wafer of the present invention, it is preferable that the wafer has a gallium nitride based semiconductor region having a threading dislocation density of 1 × 10 ⁷ cm ⁻² or less. According to this epitaxial wafer, since the influence of dislocation is reduced on the surface morphology of the semiconductor stack grown on the low dislocation region, the characteristics derived from the semipolar plane and the high indium composition become clear.

  In the epitaxial wafer of the present invention, the wafer includes a plurality of first and second regions alternately arranged in a second direction intersecting the first direction, and the first region includes the first region The second region has a threading dislocation density greater than the first threading dislocation density, and the first region is formed on the wafer. It can extend in a third direction that intersects the second direction from one point on the edge to another point on the edge. According to this epitaxial wafer, a semiconductor laser can be fabricated in a low dislocation region of a large-diameter GaN wafer.

  In the epitaxial wafer of the present invention, it is preferable that the cleaved crystal plane is substantially orthogonal to the third direction.

  In the epitaxial wafer of the present invention, the first direction is preferably an m-axis direction. According to this epitaxial wafer, the m-plane is easy to cleave.

  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, according to the present invention, a nitride semiconductor laser having a cleavage plane of good quality is provided. The present invention also provides a method for producing this nitride semiconductor laser. Furthermore, according to the present invention, an epitaxial wafer for the nitride semiconductor laser is provided.

  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 nitride semiconductor laser, the method of manufacturing the nitride semiconductor laser, and the epitaxial wafer for the nitride semiconductor laser 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.

  FIG. 1 is a drawing schematically showing a structure of a semiconductor laser according to the present embodiment. The nitride semiconductor laser 11 includes a support base 13 and a semiconductor stack 15. In FIG. 1, an orthogonal coordinate system S is shown. The support base 13 is made of a hexagonal nitride semiconductor, for example, a gallium nitride semiconductor such as GaN, an aluminum nitride semiconductor, or the like. The support base 13 has a main surface 13a and a back surface 13b inclined in a predetermined direction from the c-plane of the hexagonal nitride semiconductor. The inclination angle of the main surface 13a of the support base 13 is 20 degrees or more, and the inclination angle is 40 degrees or less. The inclination angle of the c-axis of the hexagonal nitride semiconductor is indicated by the vector C shown in FIG. An alternate long and short dash line 13 c indicates a typical c-plane of the hexagonal nitride semiconductor in the support base 13. The semiconductor stack 15 is provided on the main surface 13 a of the support base 13. The semiconductor stack 15 includes a plurality of semiconductor films for a semiconductor laser, and includes, for example, a first conductivity type nitride semiconductor layer 21, an active layer 23, and a second conductivity type nitride semiconductor layer 25. The first conductivity type nitride semiconductor layer 21, the active layer 23, and the second conductivity type nitride semiconductor layer 25 are sequentially arranged in a direction intersecting the main surface 13 a of the support base 13 (Z-axis direction). The active layer 23 is provided between the first conductivity type nitride semiconductor layer 21 and the second conductivity type nitride semiconductor layer 25. The active layer 23 has a gallium nitride based semiconductor layer containing indium, and the gallium nitride based semiconductor layer has an indium composition of 0.2 or more. The surface 15a of the semiconductor stacked layer 15 has a plurality of protrusions 19a extending in a first direction (for example, the X-axis direction), and the plurality of protrusions 19a are in a second direction (for example, intersecting the first direction) In the Y-axis direction). The semiconductor stacked layer 15 has first and second cleaved surfaces 17a and 17b extending in the second direction.

  According to the nitride semiconductor laser 11, a semiconductor layer having a high indium composition of 0.2 or more is included in the active layer 23. For this reason, the surface 15a of the semiconductor stack 15 exhibits a morphology including a plurality of protrusions 19a extending in the first direction. The height of the protrusions 19a is, for example, about 0.5 to 2 nm, and the protrusion density per unit length is, for example, about 0.1 to 5 / nm. Since the first and second cleaved surfaces 17a and 17b of the semiconductor stack 15 are formed to extend in the second direction, the quality of the cleaved surface is improved and the yield of cleavage is also good.

  In the nitride semiconductor laser 11, the inclination angle of the main surface 13a of the support base 13 is preferably larger than 20 degrees. Since the off-angle from the c-plane is large, the characteristics of the semiconductor laser mainly show characteristics derived from the semipolar plane rather than characteristics derived from the c-plane.

  FIG. 2A is a drawing showing a sketch of the surface morphology observed in the semiconductor stack 15 grown on the wafer in which the X-axis direction of FIG. 1 coincides with the <10-10> direction. This observation was performed using an atomic force microscope. Since the stable surface in crystal growth is the m-plane, each protrusion 19b extends in the m-axis direction while meandering. As a whole, the protrusion 19a extends in the m-axis direction. Symbol Dc indicates the inclination direction of the c-axis. The direction Dc is substantially orthogonal to the m-axis.

  FIG. 2B is a drawing showing a sketch of a cross-section of the surface morphology of the semiconductor stack 15 shown in FIG. This cross section is taken along the line I-I shown in FIG. FIG. 2B shows a coordinate system CR indicating the main crystal axes of hexagonal nitride. The vector N indicates a normal vector of the main surface 13a of the support base 13, and the vector C indicates the c-axis direction of the semiconductor stack 15 epitaxially grown on the support base 13, that is, the c-axis direction of the support base 13. . The vector N forms an angle θ with the vector C. As shown in FIG. 2A, the protrusions 19b extend in the first direction (for example, <10-10> direction) and are arranged in the second direction (for example, <11-20> direction). ing. As shown in FIG. 2B, the typical structure of the protrusion 19b includes the surface Sc and the surface Sa as main constituent surfaces, and can further include higher-order crystal surfaces. The surface Sc is a c-plane, and the surface Sa is a-plane. According to the arrangement of the protrusions 19b, a suitable cleavage surface is formed.

  FIG. 3 shows the surface morphology observed in the semiconductor stack 15 grown on the wafer where the c-axis tilt direction of the support substrate 13 is off by a slight angle δ with respect to the a-axis (<11-20>) direction. It is drawing which shows the sketch of. When the direction in which the c-axis of the support base 13 is tilted is slightly shifted with reference to the a-axis of the support base 13, the regularity of the arrangement of the protrusions becomes high in the surface morphology of the semiconductor stack 15. According to the experiments by the inventors, the range of inclination of the c-axis that enhances the regularity is preferably such that the absolute value of the angle from the a-axis of the hexagonal nitride semiconductor is 0.1 degree or more. In order to obtain suitable laser cavity characteristics including the cleaved surfaces 17a and 17b of the semiconductor laser, the absolute value of the incident angle of light with respect to each of the cleaved surfaces 17a and 17b is preferably 1 degree or less. It is not directly related to the regularity of the protrusion arrangement. The inclination direction of the c-axis is preferably in an angle range of −1 degree to −0.1 degree and +0.1 degree to +1 degree from the <11-20> direction. In the nitride semiconductor laser 11, since the m-plane is easy to cleave, the first and second cleaved surfaces 17a and 17b are preferably m-planes.

  InGaN performs two-dimensional nuclear growth. The growth rate, indium composition, and the like affect the density of protrusions and the interval between protrusions on the surface 15a of the semiconductor stack 15. According to the experiments by the inventors, when the regularity of the protrusion interval increases, the microscopic uniformity is improved with respect to the film thickness and composition of the InGaN layer. As a result, the full width at half maximum in the emission spectrum of the semiconductor laser 11 is reduced. Further, the gain of the semiconductor laser 11 is improved and the oscillation threshold can be lowered.

  In a Fabry-Perot laser, the flatness of the cleaved surface is important when used in a laser cavity that utilizes a cleaved surface. Morphological irregularities on the surface of the epitaxial film grown on the wafer and on the back surface of the wafer affect the quality of the cleavage plane. When the regularity of the protrusions on the surface 15a of the semiconductor laminate 15 is increased, the morphological regularity is increased, the quality of the cleavage plane is improved, and the cleavage yield is also improved.

According to the inventors' experiments, this tendency is observed in InGaN with a high indium composition. For example, the In composition X of the In _X Ga _1-X N well layer of the active layer 23 is preferably 0.2 or more. Moreover, since defect density will become high when In composition is too high, it is preferable that In composition X is 0.5 or less.

In the nitride semiconductor laser 11, the support base 13 preferably has a low dislocation gallium nitride semiconductor region having a threading dislocation density of 1 × 10 ⁷ cm ⁻² or less. Since the first conductivity type nitride semiconductor layer 21, the active layer 23, and the second conductivity type nitride semiconductor layer 25 are grown on the low dislocation gallium nitride semiconductor region, the influence of dislocations on the surface morphology of the semiconductor stack 15. Is reduced, and the characteristics derived from the semipolar plane and the high indium composition become clear.

  Although described in detail later, the support base 13 can have the following structure. The support base 13 can include a first region having a threading dislocation density smaller than the first threading dislocation density, and a second region having a threading dislocation density larger than the first threading dislocation density. The first region can extend in a predetermined direction and a direction substantially orthogonal to the c-axis direction of the hexagonal nitride semiconductor. The semiconductor laser 11 including the support base 13 can be manufactured using a large-diameter GaN wafer having such a structure.

  With reference to FIG. 1 again, the nitride semiconductor laser 11 will be further described. The first conductivity type nitride semiconductor layer 21 includes, for example, an n-type cladding layer 31 and may include an n-type buffer layer 33 if necessary. The active layer 23 is included in the optical waveguide region 35. If necessary, the optical waveguide region 35 may include a first light guide layer 37a and a second light guide layer 37b. The active layer 23 is located between the first light guide layer 37a and the second light guide layer 37b. The second conductivity type nitride semiconductor layer 25 can include, for example, a p-type cladding layer 39 and a p-type contact layer 41.

  The surface 15 a of the semiconductor stack 15 is covered with an insulating film 43. An opening 43 a is provided in the insulating film 43. The p-type contact layer 41 and the insulating film 43 are provided with an electrode 45, and the electrode 45 (for example, an anode) is connected to the contact layer 41 through an opening 43a. Further, another electrode (for example, a cathode) 47 is provided on the back surface 13 b of the support base 13. In this embodiment, the electrode 47 is provided on the entire back surface 13b. The electrode 45 extends in a direction from one of the cleavage surfaces 17a and 17b to the other of the cleavage surfaces 17a and 17b. The electrode 45 has a stripe shape extending along the extending direction of the laser cavity. This provides a semiconductor laser with good characteristics.

  The active layer 23 can be, for example, a quantum well structure 49. The quantum well structure 49 can include a well layer 49a and a barrier layer 49b. The well layers 49a and the barrier layers 49b are alternately arranged. Preferably, the well layer 49a can be made of a gallium nitride based semiconductor containing indium, such as InGaN. The barrier layer 49b can be made of a gallium nitride based semiconductor having a larger band gap than the well layer 49a, and is made of, for example, InGaN or GaN.

  The emission wavelength of the semiconductor laser 11 can be 450 nm or more and 550 nm or less. In accordance with such a wavelength range, the range of In composition in the InGaN well layer is 0.2 or more and 0.4 or less. Further, the thickness range in the InGaN well layer is 1 nm or more and 10 nm or less. The emission wavelength of the semiconductor laser 11 can be, for example, a green wavelength range from a practical standpoint.

4 and 5 are drawings showing the main steps of the method of manufacturing the epitaxial wafer and the nitride semiconductor laser according to the present embodiment. The epitaxial film in the manufacturing process is produced, for example, by metal organic vapor phase epitaxy. Trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI), ammonia (NH ₃ ) are used as raw materials, and silane (SiH ₄ ) and biscyclopentadienyl magnesium (CP ₂ Mg) are used as dopants. Is used.

As shown in FIG. 4A, a wafer 51 made of a hexagonal nitride semiconductor is prepared. Wafer 51 has a main surface 51a and a back surface 51b inclined in a predetermined direction from the c-plane of a hexagonal nitride semiconductor. The main surface 51a and the back surface 51b are produced so as to be substantially parallel to each other. The off angle of the main surface 51a of the wafer 51 is 20 degrees or more. This is because the piezo generated in the light emitting layer containing In grown on this wafer (especially with a light emission wavelength of 500 nm or more) can be reduced and efficiency can be improved compared to the c-plane. The inclination angle is 40 degrees or less. This is because the morphology of the epitaxial film grown on the wafer deteriorates above this angle. The off-angle is defined by sqrt (θ _M ² + θ _A ² ) using the inclination angle θ _M in the m-axis direction and the inclination angle θ _A in the a-axis direction, and the symbol “sqrt” calculates the square root. Show. The shape of the wafer 51 can be substantially disk-shaped. It is preferable to use a wafer having a maximum distance between two points on the edge 51c of the wafer 51 of 45 mm or more (for example, 2 inches). The hexagonal nitride semiconductor is, for example, GaN. The GaN wafer is, for example, oxygen-doped, and the electron carrier concentration is, for example, 1 × 10 ⁷ cm ⁻³ to 1 × 10 ⁹ cm ⁻³ . The thickness of the GaN wafer is, for example, about 300 micrometers.

  As shown in FIG. 4B, the first conductivity type nitride semiconductor layer 53 is formed on the wafer 51. The first conductivity type nitride semiconductor layer 53 may include one or more gallium nitride based semiconductor films. The first conductivity type nitride semiconductor layer 53 can include, for example, an n-type GaN buffer layer and an n-type AlGaN cladding layer.

  As shown in FIG. 4C, after forming the first conductivity type nitride semiconductor layer 53, a light guide layer 55a is formed on the wafer 51 if necessary. The light guide layer 55a is made of a gallium nitride based semiconductor having a refractive index larger than that of the cladding layer, and is made of, for example, GaN or InGaN. Next, as shown in FIG. 5A, after forming the light guide layer 55 a, the active layer 57 is formed on the wafer 51. As described above, the active layer 53 can include one or a plurality of gallium nitride based semiconductor layers, and can have, for example, a multiple quantum well structure. Thereafter, when the light guide layer 55a is formed, after the active layer 53 is grown, the light guide layer 55b is formed on the wafer 51 as shown in FIG. The light guide layer 55b is made of a gallium nitride-based semiconductor having a refractive index larger than the refractive index in the cladding layer, and is made of, for example, GaN or InGaN. The light guide layers 55a and 55b are preferably made of a material having a band gap comparable to that of the barrier layer of the active layer 57.

  As shown in FIG. 5C, the second conductivity type nitride semiconductor layer 59 is formed on the wafer 51. The second conductivity type nitride semiconductor layer 59 may include one or more gallium nitride based semiconductor films. The second conductivity type nitride semiconductor layer 59 can include, for example, a p-type AlGaN cladding layer and a p-type GaN contact layer.

  Through these steps, the epitaxial wafer E1 is manufactured. The epitaxial wafer E1 has a semiconductor laminated structure suitable for a nitride semiconductor laser. As shown in FIG. 5C, the epitaxial wafer E <b> 1 includes a wafer 51 and a semiconductor stack 61. The wafer 51 and the semiconductor stack 61 are made of a hexagonal nitride semiconductor. The tilt angle of the c-axis of the hexagonal nitride semiconductor is tilted in the same manner as the vector C shown in FIG. Not only the surface 51a of the wafer 51 but also the surface 61a of the semiconductor stack 61 is inclined in a predetermined direction from the c-plane of the hexagonal nitride semiconductor. Depending on the inclination angle of the main surface 51a of the wafer 51, the inclination angle of the surface 61a of the semiconductor stack 61 is not less than 20 degrees and not more than 40 degrees. The semiconductor stack 61 includes a plurality of semiconductor films for a semiconductor laser, and is provided on the main surface 51 a of the wafer 51. The semiconductor stack 61 includes a first conductivity type nitride semiconductor layer 53, an active layer 57, and a second conductivity type nitride semiconductor layer 59. The first conductivity type nitride semiconductor layer 53, the active layer 57, and the second conductivity type nitride semiconductor layer 59 are sequentially arranged in a direction perpendicular to the main surface 51 a of the wafer 51. The active layer 57 is provided between the first conductivity type nitride semiconductor layer 21 and the second conductivity type nitride semiconductor layer 59. The active layer 57 has a gallium nitride based semiconductor layer containing indium, and the gallium nitride based semiconductor layer has an indium composition of 0.2 or more. As shown in FIG. 5C, the morphology of the surface 61a of the semiconductor stack 61 has a plurality of protrusions extending in the first direction, and the plurality of protrusions 19a intersects the first direction. Are arranged in two directions. The hexagonal nitride semiconductor of the wafer 51 has a cleaved crystal plane extending in the second direction.

  According to this epitaxial wafer E1, the crystal plane that can be cleaved extends in the second direction intersecting the first direction. For this reason, a semiconductor layer having a high indium composition of 0.2 or more is included in the active layer, and a plurality of protrusions extend in the first direction on the surface 61a of the semiconductor stack 61. Therefore, a nitride semiconductor laser is formed using an epitaxial wafer. When produced, the cleavage yield is good.

  6 and 7 are drawings showing the main steps of a method for fabricating a nitride semiconductor laser. As shown in FIG. 6A, the first conductivity type nitride semiconductor layer 53 includes, for example, an n-type GaN buffer layer 63a and an n-type AlGaN cladding layer 63b. The second conductivity type nitride semiconductor layer 59 includes, for example, a p-type AlGaN cladding layer 65a and a p-type GaN contact layer 65b. An insulating film 67 having an opening is formed on the semiconductor stack 61 of the epitaxial wafer E1. The insulating film 67 can be made of, for example, silicon oxide. After forming the insulating film 67, an electrode 69a is formed on the surface of the epitaxial wafer E1. Next, the wafer 51 d is formed by reducing the thickness of the wafer 51. This step can be performed, for example, by grinding the back surface 51b of the wafer 51. An electrode 69b is formed on the back surface 51e of the wafer 51d. The substrate product P1 was produced through these steps. The back surface 51e is substantially parallel to the main surface 51a.

  As shown in FIG. 6B, after the electrodes 68a and 69b are formed, the epitaxial wafer E1 is cleaved to form the cleaved surfaces 71a and 71b. By cleaving, laser bars 73a, 73b and the like are formed in order. Each of the laser bars 73a and 73b has cleaved surfaces 71a and 71b facing each other. Since the m-plane is easy to cleave, the cleaved surfaces 71a and 71b are preferably m-planes. .

  The wafer 51 and the epitaxial wafer E1 have a cleavable crystal plane CL indicated by a dashed line in FIG. The laser bars 73a and 73b are produced by cleaving on the cleaved crystal plane CL. As already described, a plurality of protrusions extending in the first direction are formed on the surface of the epitaxial wafer E1, as shown in FIG. 6B. The crystal plane CL extends in a second direction that intersects the first direction. For this reason, the flatness of the cleavage plane is improved. Further, since the substrate product P1 and the epitaxial wafer E1 are cleaved in the second direction crossing the first direction, the cleavage yield is good.

  When the direction of inclination of the c-axis is an angle range of −1 degree to −0.1 degree and +0.1 degree to +1 degree from the <11-20> direction, a semiconductor layer having a high indium composition of 0.2 or more is included. In the surface morphology of the semiconductor stack 61, the regularity of the arrangement of the protrusions becomes high. The improvement of regularity is effective for the yield of cleavage.

  When the inclination angle of the main surface 51a of the wafer 51 is greater than 20 degrees, the characteristics of the semiconductor laser mainly show characteristics derived from the semipolar plane rather than characteristics derived from the c plane.

When the wafer 51 has a gallium nitride based semiconductor region having a threading dislocation density of 1 × 10 ⁷ cm ⁻² or less, the influence of dislocation is reduced on the surface morphology of the semiconductor stack grown on the low dislocation region. The characteristics derived from the semipolar plane and the high indium composition become clear. Therefore, the yield of cleavage is good.

FIG. 7 is a drawing showing an example of a wafer that can be used in the method of manufacturing an epitaxial wafer and a nitride semiconductor laser according to the present embodiment. The wafer 81 includes a plurality of first regions 83 and a plurality of second regions 85. The first region 83 extends in a first direction (for example, in the m-axis direction) from one point on the edge of the wafer 81 to another point on the edge, and the first region 83 and the second region 83 The regions 85 are alternately arranged in a second direction (for example, the direction of the a axis) that intersects the first direction. The first region 83 has a threading dislocation density of, for example, 1 × 10 ⁷ cm ⁻² or less, and the second region 85 has a threading dislocation density higher than that of the first region 83. In the semiconductor laser manufactured using the wafer 81, the laser cavity is formed on the first region 83 and extends along the first region 83. In the wafer 81, a crystal plane that can be cleaved extends in the second direction (for example, the Y-axis direction). The wafer 81 can be a GaN wafer, for example. For this reason, a semiconductor laser can be fabricated in a low dislocation region of a large-diameter GaN wafer. The extending direction of the laser cavity can be the m-axis direction. The m-plane is easy to cleave.

  According to the epitaxial wafer manufactured using the wafer 81, the influence of the dislocation is reduced on the surface morphology of the semiconductor stack grown on the low dislocation region. Clarification with semiconductor stacking.

Example 1
An epitaxial structure for a semiconductor laser was fabricated on a GaN wafer. A GaN wafer having a principal surface inclined at an inclination angle α of 0.1 degree, 10 degrees, 21 degrees, 26 degrees, and 30 degrees in the [11-20] direction of the c-axis was prepared. In the GaN wafers having respective inclination angles, the inclination angles β in the [10-10] direction were 0.02 degrees, 0.1 degrees, and 1 degree. On these 12 types of GaN wafers. The epitaxial growth of the laser diode structure was performed. The laser diode structure has a plurality of gallium nitride based semiconductor films. Epitaxial growth was performed by metal organic vapor phase epitaxy. Prior to the epitaxial growth, the surface of the GaN wafer was heat-treated using ammonia and hydrogen.

When an InGaN layer serving as a well layer is grown under the same film forming conditions on a GaN wafer having different inclinations in the [11-20] direction, the In compositions of the InGaN layers are different from each other. Specifically, as the tilt angle increases, the In composition of the InGaN layer decreases. For this reason, the growth conditions of the InGaN layer were adjusted so that an InGaN layer having substantially the same In composition was grown on GaN wafers having different inclinations. The growth conditions of the epitaxial film were performed by adjusting the growth temperature, the amount of raw material supplied, and the like. The change of the growth temperature is in the range of 600 to 760 degrees Celsius. In order to adjust the raw materials, the supply amounts of TMG and TMI were changed.
Since it is necessary for InGaN to migrate the surface, the growth rate is preferably 0.5 μm / hr or less, and more preferably 0.2 μm / hr or less. If the growth is interrupted between the well layer and the barrier layer, the surface of the InGaN layer is altered and the morphology deteriorates. It is better not to interrupt more than 1 minute between the well layer and the barrier layer, and it is desirable to grow continuously. The growth temperature range of the electronic block is 900 to 1200 degrees Celsius (° C.). The growth temperature range of the p-type cladding is 900 to 1200 degrees Celsius (° C.). The growth temperature range of the p-type contact is 900 to 1200 degrees Celsius (° C.).

An epitaxial wafer for the semiconductor laser shown in FIG. 8 was produced.
Wafer 91a: 2-inch n-type GaN wafer n-type cladding 91b: Si-doped Al _0.04 Ga _0.96 N, 2300 nm
n-side light guide 91c: undoped In _0.06 Ga _0.94 N, 100 nm
Active layer 91d: Six well barrier layers 91e: Undoped In _0.02 Ga _0.98 N, 15 nm
Well layer 91f: undoped In _0.35 Ga _0.65 N, 1.8 nm
p-side light guide 91g: undoped In _0.06 Ga _0.94 N, 100 nm
p-type electron block 91h: Mg-doped Al _0.18 Ga ₀₈₂₆ N, 20 nm
p-type cladding 91i: Si-doped Al _0.06 Ga _0.94 N, 400 nm
p-type contact 91j: Si-doped GaN, 50 nm.

  The photoluminescence (PL) of these epitaxial wafers was measured. The wavelength of the excitation light laser was 375 nm. The peak wavelength of the PL spectrum was in the range of 510 nm to 530 nm. Although the full width at half maximum of the PL spectrum of the epitaxial wafer having the tilt angle β of 0.02 degrees was 40 nm to 50 nm, the full width at half maximum of the PL spectrum of the epitaxial wafer having the tilt angles β of 0.1 degree and 1 degree is 30 nm to 40 nm. This is because this wafer has a more uniform projection interval and a uniform In composition distribution.

  A ridge structure was formed on the epitaxial wafer using photolithography and reactive ion etching. The width of the ridge structure was 1.5 μm, for example. The depth of the ridge structure is 500 nm. The ridge structure included a p-type electron block, a p-type cladding 91i, and a p-type contact 91j. After forming the ridge structure, an insulating film 91k having an opening was deposited on the ridge structure and the wafer. Thereafter, a p-side electrode 91m was formed. The back surface of the GaN wafer was ground. The thickness of the ground GaN wafer was 150 μm. An n-side electrode 91n was fabricated on the back surface of the ground GaN wafer. After these electrodes were fabricated, alloying annealing was performed to produce a substrate product.

  Next, this substrate product was cleaved on the (10-10) plane so as to have a laser cavity length of 600 μm, thereby producing a laser bar. When the cleaved surface was observed using an optical microscope, 70% of the laser bars produced from the substrate product having an inclination in the [10-10] direction of 0.02 degrees had a streak pattern on the cleaved surface. Observed. In the laser bar produced from substrate products with inclinations in the [10-10] direction of 0.1 degrees and 1.0 degrees, a streaky pattern is not observed on the cleavage plane, and a good mirror surface is formed by cleavage. It had been. Laser bars having a mirror end face were selected from the manufactured laser bars. After forming a reflection film on the end face of the selected laser bar, the laser bar was separated to produce the semiconductor laser chip shown in FIG. A semiconductor laser device was fabricated by mounting a semiconductor laser chip on a package.

The semiconductor laser element was energized and the electrical characteristics were measured. In energization, a pulse current having a period of 5 μsec and a duty of 0.5% was applied up to 50 kAcm ⁻² .
(1) No laser oscillation was observed in a semiconductor laser device fabricated using GaN wafers inclined at 0.1 degrees and 10 degrees in the [11-20] direction of the c-axis. In these semiconductor lasers, it is considered that a large piezo electric field lowers the emission recombination probability.
(2) No laser oscillation was observed in a semiconductor laser device manufactured using a GaN wafer tilted by 0.01 degrees in the [10-10] direction of the c-axis. In these semiconductor lasers, since the full width at half maximum of the PL spectrum is large, it is considered that a gain necessary for laser oscillation is not obtained.
(3) Laser oscillation was observed in semiconductor laser devices fabricated using GaN wafers having other inclination angles. That is, a GaN wafer having a main surface inclined at an inclination angle α of 21 degrees, 26 degrees, and 30 degrees in the [11-20] direction of the c axis, and an inclination angle β in the [10-10] direction. Laser oscillation was observed in the laser diode structure fabricated on a GaN wafer with 0.1 ° and 1 °.

  A green light emitting semiconductor laser requires an epitaxial layer having a high indium composition. The off-angle dependency of the main surface of the wafer when a gallium nitride based semiconductor thin film is grown on a wafer having a semipolar surface has been shown in the present embodiment. It also shows that the surface morphology of the epitaxial film is related to InGaN with a high indium composition. Further, a growth mode peculiar to a semipolar wafer is shown in this embodiment. This growth mode is related to the cleaving property in the semiconductor laser structure.

  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.

  A light emitting device using a GaN wafer having a semipolar plane is expected as a green light source.

Light emitting elements are used as light sources for liquid crystal TVs and the like. In order to produce a white color that satisfies the white balance, it is necessary to set the light quantity ratio of the RGB light emitting elements to about 3: 6: 1. Therefore, it is necessary to increase the output of the green light emitting element. The external quantum efficiency of InGaN-based green light emitting diodes currently on the market is lower than that of red light emitting diodes and blue light emitting diodes. For example, although the external quantum efficiency reaches about 45% in the same InGaN-based blue light-emitting diode, the InGaN-based green light-emitting diode is about 20%. The reason why the external quantum efficiency of the InGaN-based green light emitting element is low is considered as follows.
(1) The lattice mismatch becomes large and the quality of the InGaN light emitting layer is lowered.
(2) Luminous efficiency decreases due to separation of electron / hole distribution due to the piezoelectric field.
In particular, the piezoelectric field generated by piezoelectric polarization caused by the distortion of the crystal structure of item (2) is a problem in physical properties and is essential for GaN-based materials. Available InGaN-based green light-emitting diodes are fabricated on a c-plane (0001) GaN substrate which is a polar plane of a GaN crystal. Since the c-axis direction is the growth axis, a piezoelectric field is generated in the light emitting element. The piezoelectric field causes separation of electrons and holes injected into the light emitting layer, and the recombination probability contributing to light emission is lowered. As a result, the external quantum efficiency of the light emitting element is lowered. The reason why a piezoelectric field is generated in the c-axis direction is that the crystal structure of the InGaN layer is distorted and piezoelectric polarization occurs. In addition to piezoelectric polarization, spontaneous polarization also occurs in the InGaN layer. However, since the piezoelectric polarization is large, the electric field due to spontaneous polarization is very small compared to the piezo electric field. In a blue InGaN-based light emitting diode, it is lower than the piezoelectric field generated in the InGaN layer of the green light emitting diode. Therefore, the luminous efficiency is high. In green light-emitting diodes, the In composition of InGaN is higher than that of blue light-emitting diodes, and the strain generated in the InGaN crystals in the green light-emitting diodes is larger than that of blue light-emitting diodes, thus increasing the piezo electric field and reducing luminous efficiency. I am letting.

  Some of the technical problems related to light emission are also related to a green light emitting semiconductor laser. On the other hand, according to the present embodiment, a semiconductor laser is provided. Since a semiconductor laser uses a semipolar plane and includes a light emitting layer having a high indium composition, it is suitable for green light emission.

FIG. 1 is a drawing schematically showing a structure of a semiconductor laser according to the present embodiment. FIG. 2A is a drawing showing a sketch of the surface morphology observed in the semiconductor stack 15 grown on the wafer in which the X-axis direction of FIG. 1 coincides with the <10-10> direction. FIG. 2B is a drawing showing a sketch of a cross-section of the surface morphology of the semiconductor stack shown in FIG. FIG. 3 shows a sketch of the surface morphology observed in a semiconductor stack grown on a wafer where the c-axis tilt direction of the support substrate is off by a slight angle δ relative to the a-axis (<11-20>) direction. It is drawing which shows. FIG. 4 is a drawing showing the main steps of a method for producing an epitaxial wafer and a nitride semiconductor laser according to the present embodiment. FIG. 5 is a drawing showing the main steps of a method for producing an epitaxial wafer and a nitride semiconductor laser according to the present embodiment. FIG. 6 is a drawing showing the main steps of the method for fabricating a nitride semiconductor laser according to the present embodiment. FIG. 7 is a drawing showing an example of a wafer that can be used in the method of manufacturing the nitride semiconductor laser according to the present embodiment. FIG. 8 shows the structure of the semiconductor laser chip.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Nitride semiconductor laser, 13 ... Support base | substrate, 13a ... Main surface of support base | substrate, 13b ... Back surface of support base | substrate, 15 ... Semiconductor laminated layer, 15a ... Surface of semiconductor laminated layer, 17a, 17b ... Cleaved surface, 19a, 19b ... Projection, 21 ... first conductivity type nitride semiconductor layer, 23 ... active layer, 25 ... second conductivity type nitride semiconductor layer, 31 ... n-type cladding layer, 33 ... n-type buffer layer, 35 ... optical waveguide region, 37a 37b ... light guide layer, 39 ... p-type cladding layer, 41 ... p-type contact layer, 43 ... insulating film, 45, 47 ... electrode, 49 ... quantum well structure, 49a ... well layer, 49b ... barrier layer, 51 ... Wafer, 51a ... main surface of wafer, 51b ... backside of wafer, 51d ... ground wafer, 51e ... ground backside, 53 ... first conductivity type nitride semiconductor layer, 55a ... light guide layer, 57 ... active layer 55b ... Light guy Layer 59 ... second conductivity type nitride semiconductor layer, E1 ... epitaxial wafer, 61 ... semiconductor stack, 61a ... surface of the semiconductor stack, 63a ... n-type GaN buffer layer, 63b ... n-type AlGaN cladding layer, 65a ... p-type AlGaN cladding layer, 65b ... p-type GaN contact layer, 67 ... insulating film, 69a, 69b ... electrode, 71a, 71b ... cleavage, 73a, 73b ... laser bar, 91a ... wafer, 91b ... n-type cladding, 91c ... n side Light guide, 91d ... active layer, 91e ... barrier layer, 91f ... well layer, 91g ... p-side light guide, 91h ... p-type electron block, 91i ... p-type cladding, 91j ... p-type contact

Claims (20)

A support base made of a hexagonal nitride semiconductor, having a main surface and a back surface inclined in a predetermined direction from the c-plane of the hexagonal nitride semiconductor;
A semiconductor stack including a first conductivity type nitride semiconductor layer, a second conductivity type nitride semiconductor layer, and an active layer, provided on the main surface of the support base, and having a structure for a semiconductor laser;
The surface morphology of the semiconductor stack has a plurality of protrusions extending in a first direction,
The semiconductor stack has first and second cleavage planes extending in a second direction intersecting the first direction;
The inclination angle of the main surface of the support base is 20 degrees or more, the inclination angle is 40 degrees or less,
The active layer has a gallium nitride based semiconductor layer containing indium,
The indium composition of the gallium nitride based semiconductor layer is 0.2 or more,
The nitride semiconductor laser, wherein the active layer is provided between the first conductivity type nitride semiconductor layer and the second conductivity type nitride semiconductor layer.   2. The nitride semiconductor laser according to claim 1, wherein the predetermined direction is an angle range of −0.1 degrees or less and +0.1 degrees or more from a <11-20> direction.   3. The nitride semiconductor laser according to claim 2, wherein the predetermined direction is an angle range of −1 degree or more and +1 degree or less from a <11-20> direction. The support base has a gallium nitride based semiconductor region having a threading dislocation density of 1 × 10 ⁷ cm ⁻² or less,
The first conductive nitride semiconductor layer, the active layer, and the second conductive nitride semiconductor layer are located on the gallium nitride based semiconductor region. A nitride semiconductor laser according to any one of the preceding claims. The support base is made of GaN,
The support substrate includes a first region having a threading dislocation density smaller than a first threading dislocation density, and a second region having a threading dislocation density larger than the first threading dislocation density.
The nitride according to any one of claims 1 to 4, wherein the first region extends in a direction from the first cleavage plane toward the second cleavage plane. Semiconductor laser.   6. The nitride semiconductor laser according to claim 1, wherein the first and second cleavage planes are m planes.   The electrode according to any one of claims 1 to 6, further comprising an electrode extending in a direction from the first cleavage plane to the second cleavage plane and provided on a surface of the semiconductor stack. A nitride semiconductor laser according to any one of the preceding claims. A method for fabricating a nitride semiconductor laser comprising:
Preparing a wafer made of the hexagonal nitride semiconductor having a main surface and a back surface inclined in a predetermined direction from the c-plane of the hexagonal nitride semiconductor;
Growing a first conductivity type nitride semiconductor layer on the wafer;
Growing a gallium nitride based semiconductor layer for the active layer of the nitride semiconductor laser on the wafer after growing the first conductivity type nitride semiconductor layer;
Forming a second conductivity type nitride semiconductor layer on the wafer after forming the active layer, and forming an epitaxial wafer including a semiconductor stack;
Forming an electrode and forming a substrate product after forming the epitaxial wafer;
Forming a cleaved surface by cleaving the substrate product after forming the electrode,
The surface of the epitaxial wafer has a plurality of protrusions extending in a first direction intersecting the c-axis of the hexagonal nitride semiconductor,
The hexagonal nitride semiconductor of the wafer has a cleaveable crystal plane extending in a second direction intersecting the first direction;
The cleaved surface extends in the second direction;
The inclination angle of the main surface of the wafer is 20 degrees or more, and the inclination angle is 40 degrees or less,
The gallium nitride based semiconductor layer is made of a semiconductor containing indium,
The indium composition of the gallium nitride based semiconductor layer is 0.2 or more.   9. The method according to claim 8, wherein a maximum value of a distance between two points on the edge of the wafer is 45 mm or more.   The said predetermined direction is an angle range of -1 degree to -0.1 degree and +0.1 degree to +1 degree from the <11-20> direction, The Claim 8 or Claim 9 characterized by the above-mentioned. Way. 11. The method according to claim 8, wherein the wafer has a gallium nitride-based semiconductor region having a threading dislocation density of 1 × 10 ⁷ cm ⁻² or less. The wafer includes a first region having a threading dislocation density smaller than a first threading dislocation density, and a second region having a threading dislocation density larger than the first threading dislocation density.
12. The first region according to claim 8, wherein the first region extends in a direction intersecting with the predetermined direction and a c-axis direction of the hexagonal nitride semiconductor. The method described in.   The method according to claim 8, wherein the cleavage plane is an m-plane. An epitaxial wafer for a nitride semiconductor laser comprising:
A wafer comprising a hexagonal nitride semiconductor and having a main surface and a back surface inclined in a predetermined direction from the c-plane of the hexagonal nitride semiconductor;
Including a first conductivity type nitride semiconductor layer, a second conductivity type nitride semiconductor layer and an active layer, and a semiconductor stack provided on the wafer,
The surface of the semiconductor stack has a plurality of protrusions extending in a first direction;
The hexagonal nitride semiconductor of the wafer has a cleaveable crystal plane extending in a second direction intersecting the first direction;
The inclination angle of the main surface of the wafer is 20 degrees or more, and the inclination angle is 40 degrees or less,
The active layer has a gallium nitride based semiconductor layer containing indium,
The indium composition of the gallium nitride based semiconductor layer is 0.2 or more,
An epitaxial wafer, wherein the active layer is provided between the first conductive nitride semiconductor layer and the second conductive nitride semiconductor layer.   The epitaxial wafer according to claim 14, wherein the maximum value of the distance between two points on the edge of the wafer is 45 mm or more.   The predetermined direction is an angle range of -1 degree to -0.1 degree and +0.1 degree to +1 degree from a <11-20> direction, according to claim 14 or claim 15. Epitaxial wafer. The epitaxial wafer according to any one of claims 14 to 16, wherein the wafer has a gallium nitride semiconductor region having a threading dislocation density of 1 x 10 ⁷ cm ^-2 or less.   The epitaxial wafer according to any one of claims 14 to 17, wherein the first direction is an m-axis direction.   The wafer includes a plurality of first and second regions alternately arranged in the second direction, and the first region has a threading dislocation density smaller than the first threading dislocation density. The second region has a threading dislocation density greater than the first threading dislocation density, and the first region extends from one point on the edge of the wafer to another point on the edge. The epitaxial wafer according to any one of claims 14 to 18, wherein the epitaxial wafer can extend in a third direction crossing the second direction. 20. The epitaxial wafer according to claim 19, wherein the cleaved crystal plane is substantially perpendicular to the third direction.

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