JP2014086507A - Nitride semiconductor laser, nitride semiconductor laser manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser having a structure which can separately adjust current confinement and optical confinement.SOLUTION: A nitride semiconductor laser 11 comprises: an optical guide layer 25 including a second optical guide layer 25a having a first region 26a and a second region 26b which are arranged along a reference surface REF1 crossing a first axis Ax; and a ridge structure 35 lying on the first region 26a, in which the second region 26b of the second optical guide layer 25a has an n-type dopant doped at a first concentration. In the second optical guide layer 25a, the second region 26b provides potential barrier to the first region 26a. Although a carrier flowing from the ridge structure 35 to the first region 26a of the second optical guide layer 25a is guided by the second region 26b which forms potential barrier, light propagating a laser waveguide can be waveguided in the second region 26b of the semiconductor.

Description

  The present invention relates to a nitride semiconductor laser and a method for manufacturing a nitride semiconductor laser.

  In Patent Document 1 and Patent Document 2, an insulating film is formed on an exposed p-type semiconductor layer by etching the p-type semiconductor layer at the time of ridge formation in the fabrication of a nitride semiconductor laser device.

  In Patent Document 3, after a through hole is formed in a highly defective region of an n-type GaN substrate, boron, proton, and nitrogen ions are implanted into the p-type contact layer using a mask formed in accordance with the through hole. .

Japanese Patent No. 3431389 Japanese Patent No. 3776511 JP 2003-229623 A

  A nitride semiconductor laser uses a ridge structure for current confinement. Since the ridge structure defines the carrier path by the shape of the semiconductor region, the shape of the semiconductor region also defines the refractive index distribution. Therefore, the use of the ridge structure not only enhances current confinement but also enhances light confinement. However, according to the knowledge of the inventors, when the optical confinement exceeds a desired level, the characteristics of the nitride semiconductor laser deviate from the desired characteristic range. Conversely, when current confinement is insufficient, the effect appears in the characteristics of the nitride semiconductor laser such as an increase in threshold value. Thus, what is desired is to make current confinement and optical confinement separately adjustable.

  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 structure in which current confinement and optical confinement can be adjusted separately from each other. An object of the present invention is to provide a method for manufacturing a semiconductor laser.

  A nitride semiconductor laser according to the present invention includes (a) a p-side light guide region provided on a semiconductor surface made of a group III nitride semiconductor and including a first semiconductor layer made of a first group III nitride semiconductor; ) An n-side light guide region provided on the semiconductor surface and made of a Group III nitride semiconductor; and (c) an active layer provided between the n-side light guide region and the p-side light guide region. (D) a ridge structure including a p-type cladding layer. The n-side light guide region, the active layer, the p-side light guide region, and the ridge structure are sequentially arranged in the direction of the first axis to form a stacked structure, and the p-side light guide region is formed on the active layer. A first interface is formed in contact with the first semiconductor layer, and the first semiconductor layer has a first region and a second region, and the first region and the second region are along a reference plane intersecting the first axis. The ridge structure is provided on the first region of the first semiconductor layer, and the second region of the first semiconductor layer includes an n-type dopant doped at a first concentration, The second region of the first semiconductor layer provides a potential barrier to the first region of the first semiconductor layer.

  According to this nitride semiconductor laser, the first semiconductor layer in the p-side light guide region has the first region and the second region arranged along the reference plane intersecting the first axis. The first region of the first semiconductor layer has a ridge structure, and the second region of the first semiconductor layer contains an n-type dopant doped at a first concentration. In the first semiconductor layer, the second region provides a potential barrier to the first region. Although carriers flowing from the ridge structure to the first region of the first semiconductor layer are guided by the second region forming the potential barrier, light propagating through the laser waveguide can be guided through the second region of the semiconductor.

  In the nitride semiconductor laser according to the present invention, the first interface is inclined with respect to a first reference plane orthogonal to a first axis extending in the c-axis direction made of the group III nitride semiconductor, and the semiconductor surface Can be semipolar.

  According to this nitride semiconductor laser, the use of the semipolar plane enables long wavelength light emission. Separating optical confinement and current confinement allows adjustment of the far field image (FFP).

  The nitride semiconductor laser according to the present invention further includes an insulator that covers the surface of the second region of the first semiconductor layer and embeds the ridge structure in contact with a side surface of the ridge structure. The refractive index of the insulator may be lower than the refractive index of the p-side light guide region.

  According to this nitride semiconductor laser, although the insulating film covers the surface of the second region of the first semiconductor layer, carriers from the semiconductor ridge are not guided by the ridge and the insulating film, but are not guided by the first semiconductor layer. Guided by two potential barriers. On the other hand, light propagating through the laser waveguide is guided by the ridge and the insulating film.

  In the nitride semiconductor laser according to the present invention, a distance between the insulating film on the second region of the first semiconductor layer and the active layer may be 100 nm or more.

  According to this nitride semiconductor laser, when the interval is 100 nm or more, the insulating film on the second region of the first semiconductor layer can avoid kicking the light propagating through the laser waveguide.

  In the nitride semiconductor laser according to the present invention, a distance between the insulating film on the second region of the first semiconductor layer and the active layer may be 300 nm or less.

  According to the nitride semiconductor laser, the current confinement and the light confinement can be separated from the light propagating through the laser waveguide by the action of the second region of the first semiconductor layer.

In the nitride semiconductor laser according to the present invention, the p-type cladding layer is In _X1 Al _Y1 Ga _1-X1-Y1 N (0 ≦ X <0.05, 0 ≦ Y <0.20), and the In _{X1 Al Y1 Ga 1-X1-} Y1 N can may have a larger band gap than the band gap profile of the p-side optical guiding region.

  According to this nitride semiconductor laser, the p-type cladding layer can be made of GaN, AlGaN, AlInN or the like having a larger band gap than the band gap profile of the p-side light guide region.

In the nitride semiconductor laser according to the present invention, the first semiconductor layer is made of In _U1 Ga _1-U1 N, and the indium composition U1 of the first semiconductor layer is 0.02 or more and 0.05 or less. May be.

According to this nitride semiconductor laser, In _U1 Ga _1-U1 N (0.02 ≦ X ≦ 0.05) can provide an appropriate refractive index in the p-side light guide region.

  The nitride semiconductor laser according to the present invention can further include a substrate having a main surface made of a group III nitride semiconductor. The n-side light guide region, the active layer, the p-side light guide region, and the p-type cladding layer are sequentially arranged on the main surface of the substrate, and the main surface of the substrate is the III Within a range of 10 degrees or more and less than 80 degrees in the m-axis direction of the group III nitride semiconductor from the c-axis of the group III nitride semiconductor from the reference plane orthogonal to the axis extending in the c-axis direction of the group nitride semiconductor You may make it incline at the angle of. According to this nitride semiconductor laser, the first interface can be given an inclination for semipolarity.

  In the nitride semiconductor laser according to the present invention, the active layer has a single quantum well structure including a single quantum well layer or a multiple quantum well structure including a plurality of quantum well layers and a plurality of barrier layers. It may be. According to this nitride semiconductor laser, the active layer can have various structures such as a single quantum well structure and a multiple quantum well structure.

  In the nitride semiconductor laser according to the present invention, the oscillation wavelength of the active layer may be in the range of 480 nm to 550 nm. According to this nitride semiconductor laser, light having a longer wavelength than the blue band of about 450 nm can be generated.

  In the nitride semiconductor laser according to the present invention, the oscillation wavelength of the active layer may be in a range from 510 nm to 540 nm. According to this nitride semiconductor laser, long wavelength light in the green band can be generated.

  In the nitride semiconductor laser according to the present invention, the second region of the first semiconductor layer exhibits n-type conductivity, and in the first semiconductor layer, the first region has a pn junction with the second region. It may be made.

  According to this nitride semiconductor laser, when the first region forms a pn junction with the second region in the first semiconductor layer, the junction potential of the pn junction is a potential for confining carriers from the semiconductor ridge. Provides a barrier.

  In the nitride semiconductor laser according to the present invention, the n-type dopant is not activated, and in the first semiconductor layer, the first region may form a pi junction with the second region. .

  According to this nitride semiconductor laser, in the first semiconductor layer, when the first region forms a pi junction with the second region, the high specific resistance of the second region is a potential for confining carriers from the semiconductor ridge. Provides a barrier.

  In the nitride semiconductor laser according to the present invention, the n-type dopant in the second region of the first semiconductor layer may be introduced by ion implantation.

  According to this nitride semiconductor laser, the second region can be formed by introducing the n-type dopant in a self-aligned manner with respect to the ridge structure by using ion implantation.

  In the nitride semiconductor laser according to the present invention, the first region and the second region of the first semiconductor layer may include a p-type dopant.

  According to this nitride semiconductor laser, the first region and the second region of the first semiconductor layer include the p-type dopant, the n-type dopant is added to the second region, and the n-type dopant is added to the first region. Not.

  In the nitride semiconductor laser according to the present invention, the second region of the first semiconductor layer includes a second concentration of p-type dopant, and the first concentration of the second region of the first semiconductor layer is You may make it larger than a 2nd density | concentration.

  According to the nitride semiconductor laser, the second region includes a second concentration of p-type dopant, and the first concentration of the n-type dopant is the second concentration of the p-type dopant in the second region of the first semiconductor layer. Greater than.

  In the nitride semiconductor laser according to the present invention, the semiconductor surface is from a reference plane orthogonal to an axis extending in the c-axis direction of the group III nitride semiconductor, and from the c-axis of the group III nitride semiconductor to the group III The nitride semiconductor may be inclined at an angle in the range of not less than 63 degrees and not more than 80 degrees in the m-axis direction.

  According to this nitride semiconductor laser, the above angle range and plane orientation make it possible to grow InGaN having a high In composition and high composition uniformity.

  The nitride semiconductor laser according to the present invention may further include an electrode in contact with the upper surface of the ridge structure. According to this nitride semiconductor laser, carriers flowing through the ridge structure are supplied from the electrode through the upper surface of the ridge structure.

  In the nitride semiconductor laser according to the present invention, the indium composition U1 of the first semiconductor layer may be 0.04 or less.

In the nitride semiconductor laser according to the present invention, the p-side light guide region may include an undoped In _{U2Ga1 -U2N} layer. The In _{U2Ga1 -U2N} layer may be provided between the active layer and the first semiconductor layer.

According to this nitride semiconductor laser, the p-side light guide region can include an undoped In _{U2Ga1 -U2N} layer and a p-doped _{InU1Ga1 -U1N} layer.

  In the nitride semiconductor laser according to the present invention, the ridge structure includes a p-type GaN layer provided between the first region of the first semiconductor layer in the p-side light guide region and the p-type cladding layer. Further, the p-type cladding layer is in contact with the p-type GaN layer, the first semiconductor layer is in contact with the p-type GaN layer, and the active layer is in contact with the p-side light guide region. The p-side light guide region may include the p-type GaN layer.

  According to this nitride semiconductor laser, the above laminated structure can provide a refractive index profile for suitable optical confinement.

  The present invention relates to a method for fabricating a nitride semiconductor laser. The method includes (a) preparing an epitaxial substrate having an epitaxial structure including an n-side light guide region, an active layer, a p-side light guide region, and a p-doped semiconductor region; and (b) the p-doped semiconductor region. Forming a mask for the ridge structure; and (c) etching the p-doped semiconductor region and the p-side light guide region using the mask, and etching the p-side light guide region and Forming a ridge structure; and (d) performing an ion implantation of an n-type dopant into the etched p-side light guide region after forming the ridge structure. The n-side light guide region, the active layer, the p-side light guide region, and the ridge structure are sequentially arranged in the direction of the first axis to form a stacked structure, and the p-side light guide region includes a first group III nitride. A first semiconductor layer made of a physical semiconductor, wherein the first semiconductor layer has a first region and a second region, and the first region and the second region are along a reference plane intersecting the first axis. The ridge structure is provided on the first region of the first semiconductor layer, and the second region of the first semiconductor layer is introduced at a first concentration by the ion implantation. Including a dopant, the second region of the first semiconductor layer provides a potential barrier to the first region of the first semiconductor layer.

  According to the method for manufacturing the nitride semiconductor laser (hereinafter referred to as “manufacturing method”), the first semiconductor layer in the p-side light guide region is arranged along the reference plane intersecting the first axis. It has 1 area | region and 2nd area | region. The first region of the first semiconductor layer has a ridge structure, and the second region of the first semiconductor layer contains an n-type dopant doped at a first concentration. In the first semiconductor layer, the second region provides a potential barrier to the first region. Carriers flowing from the ridge structure to the first region of the first semiconductor layer are guided by the second region forming the potential barrier.

  In the manufacturing method according to the present invention, the p-side light guide region forms a first interface in contact with the active layer, and the first interface extends in a c-axis direction made of the group III nitride semiconductor. The semiconductor surface is inclined with respect to a first reference plane orthogonal to the first axis, and the semiconductor surface can exhibit semipolarity.

  According to this manufacturing method, the use of the semipolar plane enables long-wavelength light emission. Separating optical confinement and current confinement allows adjustment of the far field image (FFP).

  The manufacturing method according to the present invention may further include a step of growing an insulating film on the surface of the second region of the first semiconductor layer and on the ridge structure. The ion implantation may be performed through the insulating film. According to this manufacturing method, when an n-type dopant is introduced into the second region by ion implantation, the thin insulating film can suppress damage and contamination due to ion implantation.

  In the manufacturing method according to the present invention, the first region and the second region of the first semiconductor layer may include a p-type dopant. According to this manufacturing method, the p-type dopant in the first region and the second region of the first semiconductor layer is introduced during the epitaxial growth of the first semiconductor layer.

  In the manufacturing method according to the present invention, the oscillation wavelength of the active layer may be in the range of 480 nm to 550 nm. According to this manufacturing method, longer wave light can be generated than the blue band of about 450 nm.

  The manufacturing method according to the present invention may further include a step of performing an annealing process for activating the n-type dopant after performing the ion implantation. According to this manufacturing method, the n-type dopant introduced by ion implantation is activated by the annealing process.

  The manufacturing method according to the present invention includes a step of removing the insulating film after performing the annealing treatment, a step of forming an insulator for embedding the ridge structure after removing the insulating film, And forming an electrode in contact with the upper surface of the ridge structure after the formation.

  According to this manufacturing method, although the insulating film covers the surface of the second region of the first semiconductor layer, carriers from the semiconductor ridge are not guided by the ridge and the insulating film, but are annealed in the first semiconductor layer. Guided by the potential barrier of the second region. On the other hand, light propagating through the laser waveguide is guided by the ridge and the insulating film.

  Moreover, since the thickness of the insulating film is smaller than the height of the ridge structure, the thin insulating film substantially covers the second region and does not cover the side surface of the ridge structure. The insulating film exposed to the ion implantation is not used for protecting the ridge structure.

  In the manufacturing method according to the present invention, the second region of the first semiconductor layer exhibits n-type conductivity, and in the first semiconductor layer, the first region forms a pn junction with the second region. Can do.

  According to this manufacturing method, the second region of the first semiconductor layer is annealed and exhibits n conductivity. Carriers from the semiconductor ridge are not guided by the ridge and the insulating film, but are guided by the potential barrier of the pn junction related to the second region of the first semiconductor layer.

  The manufacturing method according to the present invention may further include a step of forming a metal film on the epitaxial substrate before the mask is formed after the epitaxial substrate is prepared. The mask may be formed on the metal film, and the metal film may be etched using the mask.

  According to this method for fabricating a nitride semiconductor laser, since the metal film is formed on the epitaxial substrate before the ridge is formed, the interface between the surface of the epitaxial substrate and the metal film can be formed while avoiding contamination of the surface of the epitaxial substrate. .

  In the manufacturing method according to the present invention, after the ion implantation, the step of removing the insulating film, the step of forming an insulator that embeds the ridge structure after removing the insulating film, and the insulator are formed. And a step of forming an ohmic electrode in contact with the upper surface of the ridge structure.

  According to this manufacturing method, the insulating film covers the surface of the second region of the first semiconductor layer during the ion implantation, but the insulating film is removed without performing annealing after the ion implantation. Carriers from the semiconductor ridge are not guided by the ridge and the insulating film, but are guided by the potential barrier in the second region of the first semiconductor layer that is not annealed. On the other hand, light propagating through the laser waveguide is guided by the ridge and the insulating film.

  Moreover, since the thickness of the insulating film is smaller than the height of the ridge structure, the thin insulating film substantially covers the second region and does not cover the side surface of the ridge structure. An insulating film exposed to ion implantation is not used as a protective insulating film having a ridge structure.

  In the manufacturing method according to the present invention, the n-type dopant is not activated, and in the first semiconductor layer, the first region can form a pi junction with the second region.

  According to this manufacturing method, since the second region of the first semiconductor layer is not annealed, the n-type dopant is not activated. Carriers from the semiconductor ridge are not guided by the ridge and the insulating film, but are guided by the potential barrier of the pi junction associated with the second region of the first semiconductor layer. The n-type dopant in the second region is not activated and the electrode is not thermally damaged.

  As described above, according to the present invention, there is provided a nitride semiconductor laser having a structure that allows current confinement and optical confinement to be adjusted separately from each other. Also. According to the present invention, a method for fabricating this nitride semiconductor laser is provided.

FIG. 1 is a drawing showing a structure related to a nitride semiconductor laser according to the present embodiment. FIG. 2 is a drawing showing a process flow in a method for producing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 3 is a drawing showing a process flow in the method for producing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 4 is a drawing schematically showing main steps in the method for producing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 5 is a drawing schematically showing main steps in the method for producing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 6 is a drawing schematically showing main steps in the method for producing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 7 is a drawing schematically showing main steps in the method for producing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 8 is a drawing schematically showing main steps in the method for producing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 9 is a drawing schematically showing main steps in the method for producing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 10 is a drawing showing a process flow in the method for producing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 11 is a drawing showing a process flow in the method for producing a group III nitride semiconductor light-emitting device according to the present embodiment. FIG. 12 is a drawing showing an example of a nitride semiconductor laser.

  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. Next, a nitride semiconductor laser and a method for manufacturing the nitride semiconductor laser according to the present embodiment 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 showing a structure related to a nitride semiconductor laser according to the present embodiment. FIG. 1 shows an orthogonal XYZ coordinate system S and a crystal coordinate system CR. Referring to FIG. 1, the nitride semiconductor laser 11 has a ridge structure. FIG. 1 shows an XYZ coordinate system S and a crystal coordinate system CR. The crystal coordinate system CR has a c-axis, a-axis, and m-axis. The orthogonal coordinate system S has an X axis, a Y axis, and a Z axis. The Z axis indicates the semiconductor stacking direction. Individual semiconductor layers and interfaces extend along a plane parallel to the XY plane.

  The group III nitride semiconductor laser 11 includes a first group III nitride semiconductor region 13, an active layer 15, and a second group III nitride semiconductor region 17. The first group III nitride semiconductor region 13 has a semiconductor surface 13a made of a hexagonal group III nitride semiconductor. The active layer 15 is provided on the semiconductor surface 13 a of the first group III nitride semiconductor region 13. The second group III nitride semiconductor region 17 is provided on the semiconductor surface 13 a of the first group III nitride semiconductor region 13.

  The light guide region 21 forms an interface in contact with the active layer 15, and this interface is inclined with respect to a first reference plane perpendicular to the first reference axis Cx extending in the c-axis direction made of a group III nitride semiconductor. In addition, the semiconductor surface 13a can exhibit semipolarity. Therefore, the semiconductor surface 13a can be a semipolar surface, and in the following description, the semiconductor surface 13a is referred to as a semipolar surface. The use of a semipolar surface allows long wavelength light emission. The c-axis made of a group III nitride semiconductor can be based on a semiconductor closer to the substrate than the active layer 15, for example, a nitride semiconductor in the first group III nitride semiconductor region or a nitride semiconductor of the substrate 39.

The active layer 15 is provided between the first group III nitride semiconductor region 13 and the second group III nitride semiconductor region 17. The oscillation wavelength of the active layer 15 can be in the range of 400 nm to 550 nm. In particular, the oscillation wavelength is preferably in the range of 480 nm to 550 nm, and more preferably, the oscillation wavelength of the active layer 15 is in the range of 510 nm to 540 nm. The active layer 15 can have a quantum well structure such as a single quantum well structure or a multiple quantum well structure. The first group III nitride semiconductor region 13, the active layer 15, and the second group III nitride semiconductor region 17 are sequentially arranged along the stacking axis Ax (the Z-axis direction of the coordinate system S). The electrode 19 is provided on the second group III nitride semiconductor region 17 and makes contact with the contact layer 29 of the second group III nitride semiconductor region 17. The semipolar surface 13a (same for the substrate main surface) is provided substantially parallel to a plane defined by the X axis and the Y axis of the coordinate system S.
The electrode 19 can make contact with the upper surface 35 a of the ridge structure 35. Carriers flowing through the ridge structure 35 are supplied from the electrode 19 through the upper surface 35 a of the ridge structure 35.

  The first group III nitride semiconductor region 13 includes a light guide layer 21 and a first cladding layer 23. The light guide layer 21 is provided on the n-type cladding layer 23. The active layer 15 is provided on the light guide layer 21. The first cladding layer 23 is made of a group III nitride semiconductor of a first conductivity type (for example, n-type). The light guide layer 21 is provided between the active layer 15 and the first cladding layer 23 and is in contact with the active layer 15. The light guide layer 21 includes a first light guide layer 21a, and includes a gallium nitride semiconductor including indium as a group III constituent element. When the first cladding layer 23 of the first group III nitride semiconductor region 13 exhibits n conductivity, the light guide layer 21 is referred to as an n-side light guide region. The second group III nitride semiconductor region 17 is provided on the active layer 15. The second group III nitride semiconductor region 17 includes another light guide layer 25 and a second cladding layer 27. The second cladding layer 27 is made of a second conductivity type (for example, p-type) group III nitride semiconductor, and is provided on the light guide layer 25. The light guide layer 25 is provided between the active layer 15 and the second cladding layer 27 and can be in contact with the active layer 15. The light guide layer 25 includes a first semiconductor layer 25a and includes a gallium nitride semiconductor including indium as a group III constituent element. In the following description, the first semiconductor layer 25a is referred to as the second light guide layer. When the second cladding layer 27 of the group III nitride semiconductor region 17 exhibits p conductivity, the light guide layer 25 is referred to as a p-side light guide region. The second group III nitride semiconductor region 17 has a ridge structure 35. If necessary, the light guide layer 25 can include a carrier blocking layer. The light guide layer (n-side light guide region) 25, the active layer 15, another light guide layer 25 (p-side light guide region), and the ridge structure 35 have a first axis Ax extending in a direction intersecting the semiconductor surface. Arranged sequentially in the direction to form a laminated structure. The active layer 15 is provided between the light guide layer (n-side light guide region) 21 and another light guide layer (p-side light guide region) 25. The light guide layer (n-side light guide region) 21, the active layer 15, and another light guide layer (p-side light guide region) 25 are arranged along the normal axis of the semiconductor surface 13a.

  The light guide layer 21 includes a third light guide layer 21b in addition to the first light guide layer 21a. The first light guide layer 21 a is located between the third light guide layer 21 b and the active layer 15 and is in contact with the active layer 15. The third light guide layer 21b is made of a semiconductor different from the semiconductor material of the first light guide layer 21a, and the band gap of the third light guide layer 21b is larger than the band gap of the first light guide layer 21a.

  The another light guide layer 25 may include a fourth light guide layer 25b and a fifth light guide layer 25c in addition to the second light guide layer 25a. The fourth light guide layer 25 b is located between the second light guide layer 25 a and the active layer 15 and is in contact with the active layer 15. The fifth light guide layer 25c is made of a semiconductor different from the semiconductor material of the second light guide layer 25a, and the band gap of the fifth light guide layer 25c is larger than the band gap of the second light guide layer 25a. The fifth light guide layer 25 c is provided between the second light guide layer 25 a and the second cladding layer 27. The thickness of the light guide layer 21 can be, for example, 150 to 600 nm, and the thickness of the light guide layer 25 can be, for example, 150 to 600 nm.

  The light guide layer 21, the active layer 15 and another light guide layer 25 constitute a core region 31, and the core region 31 is provided between the n-type cladding layer 23 and the p-type cladding layer 27. The n-type cladding layer 23, the core region 31 and the p-type cladding layer 27 constitute an optical waveguide structure. The ridge structure (semiconductor ridge) 35 can include a p-type contact layer 29, a p-type cladding layer 27, and a light guide layer 25c.

  In one embodiment, the light guide layer 25 may include a second light guide layer 25a, a fourth light guide layer 25b, and a fifth light guide layer 25c. Another light guide layer 25 is in contact with the active layer 15 to form the first interface HJ1. The second light guide layer 25a has a first region 26a and a second region 26b. The first region 26a and the second region 26b are arranged along a reference plane REF1 that intersects the axis Ax (normal axis). The ridge structure 35 is provided on the first region 26a of the second light guide layer 25a, and the second region 26b of the second light guide layer 25a includes an n-type dopant doped at a first concentration. The second region 26b of the second light guide layer 25a provides a potential barrier for the first region 26a.

  According to the nitride semiconductor laser 11, the second light guide layer 25a of the light guide layer 25 has the first region 26a and the second region 26b arranged along the reference plane REF1 intersecting the normal axis Ax. A ridge structure 35 is located on the first region 26a, and the second region 26b of the second light guide layer 25a contains an n-type dopant doped at a first concentration. In the second light guide layer 25a, the second region 26b provides a potential barrier to the first region 26a. Although carriers flowing from the ridge structure 35 to the first region 26a of the second light guide layer 25a are guided by the second region 26b forming the potential barrier, the light propagating through the laser waveguide passes through the second region 26b of the semiconductor. Can be guided. Separating optical confinement and current confinement allows adjustment of the far field image (FFP).

  The active layer 15 and the light guide layer 21 constitute a second interface HJ2. The n-type cladding layer 23 is made of a group III nitride semiconductor, and the second interface HJ2 is larger than zero with respect to a reference plane Sc extending along the c-plane of the group III nitride semiconductor of the n-type cladding layer 23. Inclined at an inclination angle ANGLE. In FIG. 1, the reference plane in the n-type cladding layer 23 (the same applies to other semiconductor layers) is substantially orthogonal to the axis (axis indicated by the vector VC) indicating the c-axis direction of the crystal coordinate system CR. The active layer 15 and the light guide layer 25 constitute a first junction HJ1. First junction HJ1 is inclined at an inclination angle ANGLE greater than zero with respect to reference plane Sc extending along the c-plane of the group III nitride semiconductor of n-type cladding layer 23.

  The nitride semiconductor laser 11 can further include an insulator 43. The insulator 43 covers the surface 26c of the second region 26b and is in contact with the side surface 35b of the ridge structure 35 to embed the ridge structure. The refractive index of the insulator 43 is lower than the refractive index of the p-side light guide region 25. Although the insulating film 43 covers the surface 26c of the second region 26b, carriers from the ridge structure 35 are not guided by the insulating film 43 that defines the shape of the ridge, but by the potential barrier of the second region 26b of the semiconductor. After reaching the active layer. On the other hand, light propagating through the laser waveguide is guided by the ridge structure 35 and the insulating film 43 without being affected by the second region 26b of the semiconductor.

  The thickness of the insulator 43 is substantially equal to the height of the ridge structure. This thick insulating film covers the surface of the second region and the side surface of the ridge structure. The cap insulating film at the time of ion implantation is not used for protecting the ridge structure.

  The ridge structure 35 includes a third junction HJ3 between the light guide layer 25 and the p-type cladding layer 27. The third junction HJ3 is inclined at an inclination angle ANGLE greater than zero with respect to the reference plane Sc extending along the c-plane of the group III nitride semiconductor of the n-type cladding layer 23. The third junction HJ3 terminates at the side surface 35b of the ridge structure 35. The ridge structure 35 has a top TOP and a bottom BOTTOM. The upper surface 35 a of the semiconductor ridge 35 forms a junction J 0 with the electrode 19. The distance D between the insulating film 43 on the second region 26b and the active layer 15 may be 100 nm or more. When this interval is 100 nm or more, the insulating film 43 on the second region 26b can avoid kicking light propagating through the laser waveguide. The distance D between the insulating film 43 on the second region 26b and the active layer 15 may be 300 nm or less. With the function of the second region 26b, current confinement and light confinement can be separated from light propagating through the laser waveguide. The width of the ridge structure (BOTTOM) is, for example, in the range of 1.0 μm to 5.0 μm.

  The active layer 15 includes at least one well layer 33a, and the well layer 33a is made of, for example, a gallium nitride based semiconductor. In one embodiment, the well layer 33a can include a ternary InGaN layer. The well layer 33a contains compressive strain. The well layer 33a can include, for example, an InGaN layer. The active layer 15 can include a plurality of well layers 33a and at least one barrier layer 33b, if necessary. A barrier layer 33b is provided between adjacent well layers 33a. The outermost layer of the active layer 15 can be a well layer. The barrier layer 33b can be made of, for example, GaN or InGaN.

  As already described, the group III nitride semiconductor region 17 has the semiconductor ridge 35. The ridge 35 structure includes a part of the light guide layer 25, a p-type cladding layer 27, and a p-type contact layer 29. The light guide layer 25 is provided in contact with the p-type cladding layer 27, and the p-type contact layer 29 is provided in contact with the p-type cladding layer 27. In this embodiment, the semiconductor ridge 35 has an mc plane defined by the c-axis and m-axis of the group III nitride semiconductor of the n-type cladding layer 23 (or ac defined by the c-axis and a-axis. Surface). Further, in this embodiment, the semiconductor ridge 35 has the mn plane defined by the normal axis of the main surface of the n-type cladding layer 23 (or the normal direction of the substrate main surface 39a) and the m axis (or the above-mentioned It extends along the normal axis and the a-n plane defined by the a-axis. The c-axis of the group III nitride semiconductor can be inclined along the mn plane (or the an plane). The group III nitride semiconductor laser 11 includes end faces 37a and 37b. In one embodiment, the end faces 37a and 37b can constitute an optical resonator. A dielectric multilayer film 47 can be provided on at least one of the end faces 37a and 37b. Further, when the ridge structure 35 extends along the mn plane, an optical transition capable of reducing the threshold current can be used for laser oscillation. This can contribute not only to the confinement capability related to the ridge structure 35 but also to the reduction of the threshold current.

  According to the group III nitride semiconductor laser 11, the second group III nitride semiconductor region 17 has the ridge structure 35, and the ridge structure 35 can confine a current to the active layer 15 according to the width thereof. At the same time, the optical confinement in the second group III nitride semiconductor region 17 is also affected. Although the second region 26b of the second light guide layer 25 in the group III nitride semiconductor laser 11 is made of a semiconductor, an electron barrier is formed against carriers. Therefore, the second region 26b of the second light guide layer 25 has a refractive index different from that of an insulator such as silicon oxide, but can prevent the spread of current as in the case of an insulator such as silicon oxide. Therefore, the shape and / or structure (thickness, depth, etc.) of the second region 26b of the second light guide layer 25 can be combined with the ridge structure 35 to enable separation control between light confinement and current confinement. To do.

In the nitride semiconductor laser 11, the p-type cladding layer 27 is In _X1 Al _Y1 Ga _1-X1-Y1 N (0 ≦ X1 <0.05, 0 ≦ Y1 <0.20), and this In _X1 Al _Y1 Ga _1-X1-Y1 N may have a larger band gap than the band gap profile of the p-side light guide region. The p-type cladding layer 27 can be made of GaN, AlGaN, AlInN or the like having a band gap larger than the band gap profile of the light guide layer 25.

The second light guide layer 25a of the light guide layer 25 may be made of _{InU1Ga1 -U1N} , and the composition U1 of indium in the second light guide layer 25a may be 0.02 or more and 0.05 or less. In _U1 Ga _1-U1 N (0.02 ≦ U1 ≦ 0.05) can provide an appropriate refractive index in the p-side light guide region. The indium composition U1 of the second light guide layer 25a may be 0.04 or less. At this time, when the indium composition U1 of the second light guide layer 25a is 0.04 or less, misfit dislocation due to the influence of lattice strain does not occur, and good crystallinity can be obtained.

In the nitride semiconductor laser 11, the n-type cladding layer 21 is In _X2 Al _Y2 Ga _1-X2-Y2 N (0 ≦ X2 <0.05, 0 ≦ Y2 <0.20), and this In _X2 Al _Y2 Ga _1-X2-Y2 N may have a larger band gap than the band gap profile of the n-side light guide region. The n-type cladding layer 21 can be made of GaN, AlGaN, AlInN, or the like having a larger band gap than the band gap profile of the light guide layer 21.

The first light guide layer 21a of the light guide layer 21 may be made of In _V1 Ga ₁ -V1N, and the indium composition V1 of the second light guide layer 25a may be 0.02 or more and 0.05 or less. In _V1 Ga _1-V1 N (0.02 ≦ V1 ≦ 0.05) can provide an appropriate refractive index in the p-side light guide region. The indium composition V1 of the first light guide layer 21a may be 0.04 or less. At this time, when the composition V1 of indium in the first light guide layer 21a is 0.04 or less, misfit dislocation due to the influence of lattice strain does not occur, and good crystallinity can be obtained.

The light guide layer 25 may include an undoped In _{U2Ga1 -U2N} layer (for example, the light guide layer 25b). The In _{U2Ga1 -U2N} layer may be provided between the active layer 15 and the light guide layer 25a. The light guide layer 25 may include an undoped In _{U2Ga1 -U2N} layer (for example, a light guide layer 25b) and a p-doped _{InU1Ga1 -U1N} layer (for example, a light guide layer 25a). The light guide layer 25b includes a first region and a second region. The light guide layer 25b is provided between the first region 26a of the light guide layer 25a and the active layer 15, and between the second region 26b of the light guide layer 25a and the active layer 15. And the second region.

  The ridge structure 35 can further include a p-type GaN layer (for example, the light guide layer 25 c) provided between the first region 26 a in the light guide layer 25 and the p-type cladding layer 27. The light guide layer 25c is in contact with the p-type cladding layer 27, and the light guide layer 25a is in contact with the light guide layer 25c. The active layer 15 may be in contact with the light guide layer 25, and the light guide layer 25 may include a p-type GaN layer in the ridge structure 35. The laminated structure of the light guide described above can provide a refractive index profile for suitable light confinement. The light guide layer 25 c is provided between the first region 26 a of the light guide layer 25 a and the p-type cladding layer 27.

  Since the first region 26a and the second region 26b of the light guide layer 25a are formed in the same process, the first region 26a and the second region 26b of the light guide layer 25a as formed are substantially the same. Made of material, having the same dopant species and the same dopant concentration. However, after the ridge structure 35 is formed, an n-type dopant is introduced into the second region 26b of the light guide layer 25a by ion implantation, and the ridge structure 35 serves as a mask in the first region 26a of the light guide layer 25a. No n-type dopant is introduced by ion implantation. Therefore, by utilizing ion implantation, the n-type dopant can be introduced in a self-aligned manner with respect to the ridge structure, and the second region 26b can be formed separately from the first region 26a. The first region 26a and the second region 26b may include a p-type dopant. After the epi growth, a p-type dopant activation process is performed by an appropriate method, and the first region 26a and the second region 26b contain the activated p-type dopant. The n-type dopant is added to the second region 26b and the n-type dopant is not added to the first region 26a. The first region of the light guide layer 25b is provided between the first region 26a of the light guide layer 25a and the active layer, and the second region 26b of the light guide layer 25b is separated from the second region 26a of the light guide layer 25a. It is provided between the active layers. The light guide layer 25 c is included in the ridge structure 35 and is provided between the first region 26 a of the light guide layer 25 a and the p-type cladding layer 27. The light guide layer 25c includes a third concentration of p-type dopant. The third concentration of the light guide layer 25c is higher than the p-type dopant of the light guide layer 25a.

Example 1
The second region of the light guide layer 25a may exhibit n-type conductivity, and in the light guide layer 25a, the first region 26a may form a pn junction with the second region 26b. In the optical guide layer 25a, when the first region 26a forms a pn junction with the second region 26b, the junction potential of the pn junction provides a potential barrier for confining carriers from the semiconductor ridge. The n-type dopant introduced into the second region 26b of the light guide layer 25a by ion implantation is activated to generate electron carriers. Second region 26b has a first concentration of n-type dopant and a second concentration of p-type dopant. The first concentration is greater than the second concentration.

(Example 2)
The n-type dopant is not activated, and the first region 26a may form a pi junction with the second region 26b in the light guide layer 25a. When the first region 26a forms a pi junction with the second region 26b in the light guide layer 25a, the high specific resistance of the second region 26b provides a potential barrier for confining carriers from the semiconductor ridge. Second region 26b has a first concentration of n-type dopant and a second concentration of p-type dopant. The first concentration may be greater than the second concentration.

(Example 3)
In this embodiment, current confinement is performed in a region where p-GaN (p-InGaN) is made n-type by Si implantation, for example. Since there is no refractive index difference between the n-type region in the p-side semiconductor region and the p-type region (laser waveguide) inside it, no optical confinement occurs in the horizontal direction. On the other hand, in order to implant silicon into a semiconductor layer having a magnesium concentration lower than that of the cladding layer, etching for ridge formation is performed until the semiconductor to be ion implanted is exposed. For example, a silicon oxide film (for example, 20 nm) is grown on the light guide layer having an Mg concentration of 1 × 10 ¹⁸ cm ⁻³ before ion implantation as a protective layer from ion implantation damage. Through this insulating film, silicon ions are implanted with an acceleration energy of 40 to 120 keV and a dose of 6E + 13 to 3E + 15 cm ⁻² . If necessary, the dose and / or acceleration energy can be changed to perform multiple implantations, but the number of ion implantations may be one. After the ion implantation, the covering silicon oxide film is removed. In addition to the covering silicon oxide film, a protective silicon insulating film (for example, 300 nm) is formed by vapor deposition. When current confinement is performed using an ion-implanted semiconductor region formed by Si ion implantation, the horizontal FFP divergence angle of the green semiconductor laser can be reduced to 12 degrees or less.

  The group III nitride semiconductor laser 11 according to the present embodiment will be described with reference to FIG. 1 again. The nitride semiconductor laser 11 can further include a substrate 39. The substrate 39 has a semipolar main surface 39a and a back surface 39b made of a hexagonal group III nitride semiconductor. This semipolar main surface 39a is with respect to a second reference surface (for example, surface Sc) orthogonal to a second reference axis (axis Cx indicated by vector VC) extending in the c-axis direction of the group III nitride semiconductor. The angle formed by the inclined semipolar main surface 39a and the reference surface Sc (substantially equal to the angle ANGLE) can be in the range of 10 degrees to less than 80 degrees or 100 degrees to 170 degrees. The first group III nitride semiconductor region 13, the active layer 15, and the second group III nitride semiconductor region 17 are arranged on the semipolar main surface 39a along the normal axis (vector NV), and more specifically, n The mold cladding layer 21, the light guide layer 21, the active layer 15, another light guide layer 25, the p-type cladding layer 27, and the p-type contact layer 29 are sequentially arranged on the main surface 39 a of the substrate 39. Another electrode 49 is provided on the back surface 39 b of the substrate 39.

  The surface of each semiconductor layer in the group III nitride semiconductor layer epitaxially grown on the substrate 39 inherits the plane orientation of the semipolar plane of the substrate 39 and has a semipolar property. Therefore, the surfaces of the first group III nitride semiconductor region 13, the active layer 15, and the second group III nitride semiconductor region 17 can have a plane orientation corresponding to the plane orientation of the semipolar plane of the substrate 39. An inclination for semipolarity can be imparted to the interfaces HJ1, HJ2, and HJ3.

  The group III nitride semiconductor laser 11 includes an electrode 49 that is in contact with the back surface 39 b of the substrate 39. The substrate 39 can include a hexagonal conductive group III nitride, for example, any one of GaN, InGaN, AlGaN, and InAlGaN. Any of GaN, InGaN, AlGaN, and InAlGaN can be applied to the group III nitride semiconductor laser 11. The substrate 39 can be made of GaN, for example. The InGaN layer coherently epitaxially grown on the GaN substrate contains compressive strain.

  In addition, the inclination angle ANGLE related to the c-axis can be in the range of not less than 63 degrees and not more than 80 degrees in the inclination along the mn plane. The semipolar surface 39a having the inclination angle ANGLE described above enables homogeneous In incorporation and growth of a gallium nitride based semiconductor having a high In composition. In addition, the angle formed by the semipolar main surface 39a of the substrate 39 and the reference surface Sc can be in the range of not less than 63 degrees and not more than 80 degrees. According to the group III nitride semiconductor laser 11, the substrate 39 having a c-axis inclination in the range of not less than 63 degrees and not more than 80 degrees provides a plane orientation suitable for the production of the active layer 15 suitable for long-wavelength laser oscillation. it can. In the long wavelength region, the refractive index difference in the group III nitride semiconductor becomes small, and it becomes difficult to achieve the desired optical confinement.

  In the group III nitride semiconductor laser 11, the normal Ax of the main surface 39 a of the substrate 39 is inclined with respect to the c-axis of the group III nitride of the substrate 39, and the inclination angle of this inclination is 10 degrees or more and 80 degrees. It can be in the following range. When the c-axis of the group III nitride has an inclination of less than 10 degrees, the main surface 39a exhibits a property close to a polar surface. When the inclination of the c-axis of the group III nitride semiconductor exceeds 80 degrees, the main surface 39a exhibits a property close to a nonpolar surface.

  The oscillation wavelength of the active layer 15 can be in the range of 480 nm to 550 nm. This group III nitride semiconductor laser 11 can provide a laser beam having a relatively long wavelength. The active layer 15 can be provided so as to generate an emission spectrum having a peak wavelength within a range of 500 nm to 550 nm. The active layer 15 that generates an emission spectrum having a peak wavelength in the range of 500 nm or more and 550 nm or less is manufactured using a semipolar plane. Furthermore, the oscillation wavelength of the active layer 15 is preferably in the range from 510 nm to 540 nm. According to the group III nitride semiconductor laser 11, a long wavelength laser beam can be provided. Because of the long wavelength, not only the refractive index difference based on the semiconductor material difference but also the optical confinement is effective by the ridge structure 35. In addition, since the ridge structure 35 contributes to both current confinement and light confinement, the thick light guide layer 21a of the first group III nitride semiconductor region 13 can be used in the group III nitride semiconductor laser 11 without greatly changing the current confinement. The optical confinement and the current confinement can be easily adjusted.

  The active layer 15 includes an InGaN well layer, the indium composition of the light guide layer 21a is smaller than the indium composition of the InGaN well layer, and the indium composition of the light guide layer 21a can be 2% or more. In this structure, the light guide layer 21 a having an indium composition of 2% or more can provide a refractive index difference with respect to the semiconductor layer provided between the light guide layer 21 a and the substrate 39. Further, the indium composition of the light guide layer 21a is 6% or less, which is preferably smaller than the indium composition of the ternary InGaN well layer. The light guide layer 21a having an indium composition of 5% or less provides a refractive index between the active layer 15 and the semiconductor layer provided between the light guide layer 21a and the substrate 39 for light propagating through the laser waveguide. Can do.

  The first group III nitride semiconductor region 13 may include a plurality of light guide layers. The light guide layer 21 includes, for example, light guide layers 21a and 21b, and the light guide layer 21b includes a material (for example, GaN) different from InGaN. The light guide layer 21b is provided between the light guide layer 21a and the first cladding layer 23, and the thickness of the light guide layer 21a can be larger than the thickness of the light guide layer 21b.

  The second group III nitride semiconductor region 17 may include a plurality of light guide layers. The light guide layer 25 includes, for example, light guide layers 25a, 25b, and 25c. The light guide layers 25a and 25b include InGaN, and the light guide layer 25c includes a material different from InGaN (for example, GaN). The light guide layer 25a can be 40 nm to 100 nm. The light guide layer 25b can be 20 nm to 100 nm. The light guide layer 25c can be 100 nm to 400 nm.

  The group III nitride semiconductor laser 11 can further include an ohmic electrode 19 provided on the upper surface 35 a of the ridge structure 35. The second group III nitride semiconductor region 17 further includes a contact layer 29 made of a second conductivity type group III nitride semiconductor, and the second cladding layer 27 is provided between the contact layer 29 and the light guide layer 25. The ohmic electrode 19 can make contact with the contact layer 29. Since the ohmic electrode 19 makes contact with the contact layer 29 on the upper surface 35 a of the ridge structure 35, carriers from the ohmic electrode 19 can be confined according to the width of the ridge structure 35. The ohmic electrode 19 preferably includes, for example, palladium (Pd). Palladium can provide good contact with the group III nitride semiconductor of the contact layer 29.

  The group III nitride semiconductor laser device 11 can further include a protective insulating film 43 and a pad electrode 45. The protective insulating film 43 has an opening 43 a aligned with the upper surface 35 a of the ridge structure 35 and covers the surface 17 a of the second group III nitride semiconductor region 17. The pad electrode 45 covers the upper surface of the ohmic electrode 19 and is provided on the protective film 43. The protective film 43 also covers the side surface 35 b of the ridge structure 35, and the refractive index of the protective film 43 is smaller than the refractive index of the second group III nitride semiconductor region 17. The ohmic electrode 19 is in contact with the upper surface 17a (43a) of the second group III nitride semiconductor region 17 through the opening 43a of the protective film 43. Since the refractive index of the protective film 43 is smaller than that of the second group III nitride semiconductor region 17, the protective film 43 covering the side surface 35b of the ridge structure 35 is related to light confinement.

In the group III nitride semiconductor laser element 11, the first cladding layer 23, in the n-conducting _{In X1 Al Y1 Ga 1-X1} -Y1 N (0 <X1 <0.05,0 <Y1 <0.20) Can be. The first cladding layer 23 can provide good light confinement with respect to the light guide layer 21. The second cladding layer 27 may be a p-conductive _{In X2 Al Y2 Ga 1-X2} -Y2 N (0 <X2 <0.05,0 <Y2 <0.20). The second cladding layer 27 can provide good light confinement with respect to the light guide layer.

  2 and 3 are drawings showing a process flow in the method for producing a group III nitride semiconductor light emitting device according to the present embodiment. 4 to 9 are drawings schematically showing main steps in the method of manufacturing the group III nitride semiconductor light emitting device according to the present embodiment. In the schematic diagrams of FIGS. 4 to 9, a rectangular substrate is drawn, but the shape of the substrate is not limited to this. In the following description, in order to facilitate understanding, a procedure for producing a nitride semiconductor light emitting element on a substrate having a size of one element will be described, and the reference numerals used in FIG. 1 will be used.

  In this method, in the first step S101, an epitaxial substrate including an epitaxial structure including an n-side light guide region, an active layer, a p-side light guide region, and a p-doped semiconductor region is prepared. A substrate for forming an epitaxial growth layer for a nitride semiconductor light emitting device is prepared. The substrate (reference numeral “39” in the part (a) of FIG. 4) has a main surface (reference numeral “39a” in the part (a) of FIG. 1) made of, for example, a hexagonal group III nitride. The substrate 39 can be made of, for example, a hexagonal group III nitride, the hexagonal group III nitride can be made of, for example, a gallium nitride semiconductor, and the gallium nitride semiconductor includes, for example, GaN, AlN, or the like. .

  As shown in part (a) of FIG. 4, in step S <b> 101, after the substrate 39 is placed in the growth furnace 10 a, the epitaxial multilayer film 12 for the nitride semiconductor light emitting device is formed on the substrate 39. Epitaxial multilayer film 12 is a group III nitride semiconductor region, and epitaxial multilayer film 12 includes a plurality of group III nitride layers.

  In step S102, a substrate 39 is prepared. The substrate 39 has a main surface 39a made of hexagonal group III nitride, and the main surface 39a is semipolar. Epitaxial multilayer film 12 is epitaxially grown on main surface 39a made of hexagonal group III nitride. The direction of the c-axis in each of the group III nitride layers of the epitaxial multilayer film 12 coincides with the direction of the c-axis of the hexagonal group III nitride. Referring to part (a) of FIG. 4, a c-axis vector CV indicating the c-axis Cx of the hexagonal group III nitride is drawn, and a crystal coordinate system CR indicating the crystal orientation is shown. The crystal coordinate system CR has axes indicating the c-axis, a-axis, and m-axis of hexagonal group III nitride. In this embodiment, the c-axis Cx of the substrate 39 is inclined at an angle ALPHA with respect to the normal axis Nx represented by the normal vector NV of the substrate main surface 39a. In the embodiment described subsequently, the ridge structure extends along the mc plane defined by the m-axis and the c-axis. An angle ALPHA formed by the c-axis Cx of the substrate 39 and the normal axis Nx of the substrate main surface 39a can be in an angle range of 45 degrees to 80 degrees or 100 degrees to 135 degrees.

  The angle formed between the c-axis Cx of the substrate 39 and the normal axis of the semipolar main surface 12a of the epitaxial multilayer 12 (same as the normal axis Nx in this embodiment) is 45 degrees or more and 80 degrees or less, or 100 degrees or more and 135 degrees or less. Can be in the angular range. The angle formed between the c-axis of the group III nitride semiconductor of the epitaxial multilayer film 12 and the normal axis of the semipolar main surface 13a of the epitaxial multilayer film 12 (upper surface of the ridge portion in a later step) is 45 degrees or more and 80 degrees or less, or 100 degrees It is in the angle range of 135 degrees or less.

  In the growth furnace 10a, a plurality of group III nitride layers of the epitaxial multilayer film 12 are grown by, for example, a metal organic chemical vapor deposition method and are sequentially arranged in the direction of the normal axis Nx. The epitaxial multilayer film 12 can include an n-type gallium nitride based semiconductor layer 15, an n-type gallium nitride based semiconductor cladding layer 17, and an active layer 21. In order to form this structure, an n-type gallium nitride based semiconductor region 13, an active layer 15, and an n-type gallium nitride based semiconductor region 27 are grown on a substrate 39. In step S103, an n-type cladding layer 23 is grown on the substrate 39. After the n-type cladding layer 23 is grown, the n-side light guide region 21 is grown on the substrate 39 in step S104. After growing the n-side light guide region 21, the active layer 15 is grown on the substrate 39 in step S105. After the active layer 15 is grown, the p-side light guide region 25 is grown on the substrate 39 in step S106. After the growth of the p-side light guide region 25, the p-type cladding layer 27 is grown on the substrate 39 in step S107. After the p-type cladding layer 27 is grown, a p-type contact layer 29 is grown on the substrate 39 in step S108. The active layer 15 includes well layers 33a and barrier layers 33b, and the well layers 33a and barrier layers 33b are alternately arranged in the direction of the normal axis Nx of the substrate main surface 39a.

An example of the epitaxial multilayer film 12.
A film is formed using a metal organic chemical vapor deposition method.
n-type gallium nitride based semiconductor clad layer 23: Si-doped n-type InAlGaN.
n-side light guide region 21: Si-doped n-type GaN, undoped InGaN.
Active layer 15: single or multiple quantum well structure.
Well layer 33a: undoped InGaN.
Barrier layer 33b: undoped InGaN or undoped GaN.
p-side light guide region 25: undoped InGaN, Mg-doped InGaN, Mg-doped GaN.
p-type gallium nitride based semiconductor clad layer 27: Mg-doped p-type InAlGaN.
p-type gallium nitride based semiconductor contact layer 29: Mg-doped p-type GaN.
In this method, at the final stage of epi growth, a gas for a p-type dopant and a source gas are supplied to a growth furnace, and a p-doped contact layer 29 made of a group III nitride semiconductor is formed by metal organic vapor phase epitaxy. grow up. In one embodiment, the contact layer provides a semipolar major surface that forms the electrode film.

  The peak wavelength of the emission spectrum of the active layer 15 can be in the wavelength range of 480 nm to 550 nm. By using a semipolar plane, a light emitting element having a peak wavelength of an emission spectrum in a blue to green wavelength region within a range of 500 nm to 540 nm can be provided. The peak wavelength of the emission spectrum of the active layer 15 is preferably in the wavelength range of 500 nm or more and 540 nm or less. By using a semipolar plane, a light emitting element having a peak wavelength of an emission spectrum in a green wavelength region within a range of 500 nm to 540 nm can be provided.

  After the growth of the epitaxial multilayer 12 is completed, the epitaxial substrate E is taken out from the growth furnace 10a. The nitride semiconductor region of the epitaxial substrate E takes over the surface orientation of the substrate main surface 39a and exhibits a semipolar main surface. The nitride semiconductor region of the epitaxial substrate E includes an active layer 15, and this active layer 15 also has a semipolar property. Taking advantage of the semipolar property, a light emitting element having a peak wavelength of an emission spectrum in a wavelength range of 500 nm to 540 nm can be provided.

  The epitaxial substrate E taken out from the growth furnace 10a is exposed to an atmosphere containing oxygen. Next, in step S109, a mask for ridge formation is formed on the epitaxial substrate E.

  First, in step S110, a metal film for an ohmic electrode is formed on the epitaxial substrate E in the growth furnace 10b. Prior to the growth of the metal layer for the electrode, a pretreatment for removing a natural oxide film and contamination on the surface 40a of the epitaxial substrate E is performed. A wet process is performed to remove the natural oxide film and contamination, and in a preferred example, the epitaxial substrate E is immersed in an acid solution. The acid solution preferably contains hydrochloric acid, for example.

  After the acid cleaning of the epitaxial substrate E, it is preferable to arrange the epitaxial substrate E in the film forming furnace 10b immediately (for example, within 30 minutes or less) as shown in FIG. In step S110, the metal film 20 is deposited on the acid-cleaned main surface 12a. The metal film 20 can include, for example, at least one of a gold layer, a palladium layer, a platinum layer, and a Ti layer. These metals can provide good contact resistance to the nitride semiconductor semipolar plane. Preferably, Pd is used as the metal film 20. Pd is non-alloyed and has good ohmic characteristics with respect to the p-type GaN layer. The metal film 20 can be formed by, for example, a vapor deposition method. The thickness of the metal film 20 is, for example, 10 nm or more, and can be, for example, 200 nm or less.

  On the p-doped semiconductor region of the epitaxial substrate E, a mask for the ridge structure is formed. In one embodiment, a sacrificial film 22 for lift-off is formed on the metal film 31 in step S111, as shown in part (a) of FIG. The sacrificial film 22 preferably exhibits insulating properties. When the sacrificial film 22 is made of resin, the sacrificial film 22 can reduce stress from the dielectric mask to the metal film. The resin of the sacrificial film 22 can include at least one of resist, polyimide, and benzocyclobutene, for example. These resins can be processed by anisotropic etching to form a lift-off layer, which can be used for lift-off. The resin film of the sacrificial film 22 is formed by application using a film forming apparatus such as a spinner. The sacrificial film 22 contacts and covers the metal film 20.

In step S112, a dielectric film 24 is grown on the metal film 20 as shown in FIG. 5B. In the step of growing the dielectric film 24, the sacrificial film 22 is provided between the dielectric film 24 and the metal film 20. The dielectric film 24 can include a silicon-based inorganic insulating layer, AlN, TiO ₂ , and the silicon-based inorganic insulating layer can be made of, for example, silicon oxide (specifically, SiO ₂ ), SiN, or the like. The dielectric film 35 is preferably grown by a film forming apparatus to which, for example, an electron beam evaporation method or a sputtering method can be applied. According to this method, the silicon-based inorganic insulating layer can be grown by electron beam evaporation so as to protect the resin film from the heat during film formation.

  In step S113, a mask 28 having a pattern for ridges is formed on the dielectric film 35, as shown in FIG. The mask 28 can be made of, for example, a photoresist. This resist mask is created as follows, for example. After applying a photoresist on the dielectric film 24 using an applicator, the photoresist is exposed to light through a photomask with an exposure device, and the exposed photoresist is developed with a developing device. In one embodiment, the mask 28 has a stripe shape, for example. The stripe width is 2 μm, for example.

In step S114, as shown in part (a) of FIG. 6, the dielectric film 24 is etched by an etching apparatus using the mask 28 to form a dielectric mask 24a. This etching is preferably performed, for example, by an inductive coupling plasma reactive ion etching method (ICP-RIE method). According to this etching method, anisotropic etching can be realized. When the dielectric film 24 is made of silicon oxide, CHF ₃ can be used as an etchant. As an etchant for etching the dielectric film 24, a fluorine-based gas such as CHF ₃ can be used. As an etchant, at least one of CHF ₃ , CF ₄ , and CF ₄ + Ar can be used.

In step S114, as shown in FIG. 6A, the sacrificial film 22 is etched using the dielectric mask 24a to form the lift-off layer 22a. When the sacrificial film 22 is made of resin, the lift-off layer 22a is also made of resin. The etchant in the etching of the sacrificial film 22 preferably contains a fluorine gas or oxygen. As the fluorine-based gas, at least one of CF ₄ , CHF ₃ , and CHF ₃ / Ar can be used. This etching is preferably performed by, for example, an ICP-RIE method. According to this etching method, anisotropy in etching can be realized. Therefore, the width of the lift-off layer 22a is substantially the same as the width of the dielectric mask 24a, and no substantial side etching occurs in the lift-off layer 22a. The lift-off layer 22 a is in contact with the surface of the electrode film 20.

  Next, in step S115, a ridge structure is formed using the mask 28. In step S116, as shown in FIG. 6A, the metal layer 20 is etched using the dielectric mask 24a to form the electrode 19. The electrode 19 can include at least one of a gold layer, a palladium layer, and a platinum layer. For example, argon (Ar) can be used for etching the metal layer 20.

  Next, the p-doped semiconductor region and the p-side light guide region are etched using a mask (for example, the dielectric mask 24a) to form an etched p-side light guide region and a ridge structure. In one example, after the etching of the metal layer 31 is completed in step S117, the nitride semiconductor region 39 is etched to form the etched nitride semiconductor region 40. This etching is preferably performed by the ICP-RIE method. According to this etching method, anisotropy in etching and a desired ridge height can be realized. The p-side light guide region 25d is exposed by etching. In this embodiment, the Mg-doped GaN in the p-side light guide region 25 is removed by etching, and the Mg-doped InGaN is exposed. Undoped InGaN is covered with Mg-doped InGaN. Thus, the ion implanted region can include a p-type dopant.

  After the above process, the process proceeds to a process group for ion implantation. After the ridge structure is formed, n-type dopant ions are implanted into the etched p-side light guide region. In one embodiment, in step S118, the insulating film 30 is grown on the substrate while leaving the mask 28 left. An insulating film 30a is formed on the exposed p-side light guide region 25d, and the insulating film 30b is also deposited on the mask 28. The insulating film 30 can be made of, for example, a silicon oxide film. As a film forming method, an EB vapor deposition method can be applied.

  In step S119, as shown in FIG. 7A, ion implantation 42 of n-type dopant is performed on the entire surface of the substrate. The ionic species can be, for example, silicon. Since there are many structures 28, 24a, and 22a on the top surface of the ridge, the ions implanted 42 do not reach the top surface of the ridge. The ions implanted 42 are implanted into the semiconductor surface 25d through the insulating film 30a to form a doped region 26c indicated by a broken line. The doped region 26c is formed in a self-aligned manner with a ridge structure.

  In step S120, the insulating film 30 is removed. When the insulating film 30 is made of a silicon oxide film, the insulating film 30 can be removed using hydrofluoric acid. When an n-type dopant is introduced into the exposed light guide layer (second region 26b) by ion implantation, the thin insulating film 30b can suppress damage and contamination due to ion implantation.

  A doped region formed by ion implantation will be described with reference to FIG. The light guide layer 25 (p-side light guide region) includes a second light guide layer 25a made of a first group III nitride semiconductor. A first region 26a and a second region 26b are formed in the light guide layer 25a by ion implantation. The first region 26a and the second region 26b are arranged along a reference plane that intersects the normal axis of the substrate main surface 39a. A ridge structure 35 is located on the first region 26a. The second region 26b includes an n-type dopant introduced at a first concentration by ion implantation. In the second region 26b having the ion implanted state, the n-type dopant is not activated and has a high specific resistance. Therefore, the second region 26b provides a potential barrier for the first region 26a.

  In step S121, as shown in part (b) of FIG. 7, the insulating film 44 is deposited while leaving the mask film 24a and the sacrificial film 22a in order to form an insulator so as to embed the ridge structure. . The insulating film 44a includes an insulator 44a that embeds a ridge structure, and a deposit 44b formed on the mask film 24a and the sacrificial film 22a.

  In step S122, the sacrificial film 22a in the mask is lifted off to expose the metal layer 19 on the top surface of the ridge, and the deposit 44b formed on the mask film 24a and the sacrificial film 22a is removed. To do. As a result of the lift-off, as shown in FIG. 8A, a substrate product SP having a ridge structure embedded with an insulator 44a is produced.

  In step S123, an electrode is formed. For example, in order to form the pad electrode 45 on the ohmic electrode 19, a lift-off mask 47 is formed as shown in FIG. 8B. After this mask 47 is formed, a metal film for electrodes is deposited. The metal film is lifted off using the mask 47 to form a pad electrode 49 as shown in FIG. 9A. The pad electrode 49 can be made of, for example, Au or Ti / Pt / Au. Further, if necessary, after the value surface of the substrate 39 is polished, a back electrode 49 is formed on the polished surface of the substrate as shown in FIG. 9B.

  According to this manufacturing method, although the insulating film 30 covers the surface of the second region 26b during ion implantation, the insulating film 30b is removed without performing annealing after ion implantation. Since the second region 26b is not annealed, its n-type dopant is not activated. Since the n-type dopant is not activated in the second region 26b, the first region 26b forms a pi junction with the second region 26a. Carriers from the semiconductor ridge are not guided by the ridge and the insulating film, but are guided by the potential barrier of the pi junction related to the second region 26b. Since the n-type dopant in the second region 26b is not activated, the metal-semiconductor junction related to the electrode 20a is not thermally damaged.

  According to the method of manufacturing this nitride semiconductor laser (hereinafter referred to as “manufacturing method”), the light guide layer 25a of the light guide layer 25 has a first region 26a along the reference plane intersecting the normal axis. And the 2nd field 26b is formed. The second region 26b of the light guide layer 25a is formed so as to include an n-type dopant doped at a first concentration, while the first region 26a is directly under the ridge structure, and the dopant introduced during the epi growth is removed. Including. Therefore, the second region 26b provides a potential barrier for the first region 26a. Carriers flowing from the ridge structure 35 to the first region 26a are guided by the second region 26b forming a potential barrier.

  When the substrate 39 has a semipolar surface, the active layer allows long wavelength light emission. Separating optical confinement and current confinement allows adjustment of the far field image (FFP).

  10 and 11 are drawings showing a process flow in the method for producing a group III nitride semiconductor light emitting device according to the present embodiment. In order to facilitate understanding, the reference numerals used in the embodiments described with reference to FIGS. 3 and 4 are also used in this embodiment, if possible.

  In step S201, an epitaxial substrate is prepared. This preparation can be performed according to the process flow shown in FIGS. 1 and 2, for example, but is not limited thereto. In the following description, the epitaxial substrate is referred to as E.

In step S202, a ridge-shaped mask is formed on the epitaxial substrate E. In this embodiment, in order to manufacture a mask, a mask for a ridge structure is formed on the p-doped semiconductor region of the epitaxial substrate E in step S203. In one embodiment, a sacrificial film 22 for lift-off is formed on the epitaxial substrate E. The sacrificial film 22 preferably exhibits insulating properties. When the sacrificial film 22 is made of SiO ₂ , it has heat resistance against annealing (heat treatment) for ion implantation. Such a sacrificial film 22 can be produced, for example, by EB vapor deposition. The sacrificial film 22 covers the epi surface. In FIG. 5B, the sacrificial film 22 is formed on the metal film 10. However, in this embodiment, the sacrificial film 22 is epitaxial because the metal film is not formed on the epitaxial substrate E. It is formed directly on the substrate E.

In step S <b> 204, the dielectric film 24 is grown on the sacrificial film 22. In the step of growing the dielectric film 24, the sacrificial film 22 is provided between the dielectric film 24 and the epitaxial substrate E, and the metal layer is not sandwiched between them. The dielectric film 24 can include a silicon-based inorganic insulating layer, AlN, TiO ₂ , and the silicon-based inorganic insulating layer can be made of, for example, silicon oxide (specifically, SiO ₂ ), SiN, or the like. The dielectric film 35 is preferably grown by a film forming apparatus to which, for example, an electron beam evaporation method or a sputtering method can be applied. According to this method, the silicon-based inorganic insulating layer can be grown by electron beam evaporation. In FIG. 5B, a sacrificial film 22 and a dielectric film 24 are formed on the metal film 10, but in this embodiment, no metal film is formed on the epitaxial substrate E. A sacrificial film 22 and a dielectric film 24 are formed on the epitaxial substrate E.

In step S205, a mask 28 having a pattern for a ridge is formed on the dielectric film 35. The mask 28 can be made of, for example, a photoresist. This resist mask is created as follows, for example. After applying a photoresist on the dielectric film 24 using an applicator, the photoresist is exposed to light through a photomask with an exposure device, and the exposed photoresist is developed with a developing device.
In FIG. 5B, a mask 28 is formed. However, in this embodiment, since no metal film is formed on the epitaxial substrate E, the sacrificial film 22, the dielectric film 24, and the mask 28 are formed. Is formed on the epitaxial substrate E. Similar to the embodiment shown in FIG. 5B, in this embodiment, the mask 28 has, for example, a stripe shape. The stripe width is 2 μm, for example.

In step S206, the dielectric film 24 is etched with an etching apparatus using the mask 28 to form a dielectric mask 24a. This etching is preferably performed, for example, by an inductive coupling plasma reactive ion etching method (ICP-RIE method). According to this etching method, anisotropic etching can be realized. When the dielectric film 24 is made of silicon oxide, CHF ₃ can be used as an etchant. As an etchant for etching the dielectric film 24, a fluorine-based gas such as CHF ₃ can be used. As an etchant, at least one of CHF ₃ , CF ₄ , and CF ₄ + Ar can be used. In step S206, the sacrificial film 22 is etched using the dielectric mask 24a to form the lift-off layer 22a. It is preferable to use CHF ₃ or the like as an etchant in the etching of the sacrificial film 22 that is not a resist. This etching is preferably performed by, for example, an ICP-RIE method. According to this etching method, anisotropy in etching can be realized. Therefore, the width of the lift-off layer 22a is substantially the same as the width of the dielectric mask 24a, and no substantial side etching occurs in the lift-off layer 22a. In FIG. 6A, a composite mask including a dielectric mask 24a and a lift-off layer 22a is drawn. In this embodiment, this composite mask is formed directly on the epitaxial substrate E.

  Next, in step S207, as shown in FIG. 6B, a ridge structure is formed using the mask. The p-doped semiconductor region and the p-side light guide region are etched using a mask (for example, the dielectric mask 24a) to form the etched p-side light guide region and the ridge structure. In one example, in the step S207, the nitride semiconductor region 39 is etched to form the etched nitride semiconductor region 40. This etching is preferably performed by the ICP-RIE method. According to this etching method, anisotropy in etching and a desired ridge height can be realized. The p-side light guide region 25d is exposed by etching. In this embodiment, the Mg-doped GaN in the p-side light guide region 25 is removed by etching, and the Mg-doped InGaN is exposed. Undoped InGaN covers Mg-doped InGaN. Thus, the ion implanted region can include a p-type dopant.

  After the above process, the process proceeds to a process group for ion implantation. After the ridge structure is formed, n-type dopant ions are implanted into the etched p-side light guide region. In one embodiment, in step S208, the insulating film 30 is grown on the substrate while leaving the mask 28. Since the thickness of the insulating film 30 is smaller than the height of the ridge structure, the thin insulating film covers a region exposed by etching (a region to be the second region 26b) and does not cover the side surface of the ridge structure. As shown in FIG. 7A, an insulating film 30a is formed on the exposed p-side light guide region 25d, and the insulating film 30b is also deposited on the mask. The insulating film 30 can be made of, for example, a silicon oxide film. The thickness of the insulating film 30 is, for example, 20 to 50 nm, and in this embodiment, it is, for example, 30 nm.

In step S209, as shown in FIG. 7A, ion implantation 42 of n-type dopant is performed on the entire surface of the substrate. The ionic species can be, for example, silicon. Since there are many structures 28, 24a, and 22a on the top surface of the ridge, the ions implanted 42 do not reach the top surface of the ridge. The ions implanted 42 are implanted into the semiconductor surface 25d through the insulating film 30a to form a doped region 26c indicated by a broken line. The doped region 26c is formed in a self-aligned manner with a ridge structure. The ion implantation acceleration energy is 40 to 120 keV, and the total dose is 6E + 13 to 3E + 15 cm ⁻² .

  In step S210, before the insulating film 30 is removed, thermal annealing is performed for recovery of damage formed in the nitride crystal by ion implantation and activation of the dopant. The temperature of the thermal annealing is preferably 500 degrees Celsius or higher, for example, because it is a temperature necessary for activation. Also, the temperature of the thermal annealing is preferably, for example, 1000 degrees Celsius or less, and crystal deterioration occurs. The atmosphere of the thermal annealing can be, for example, 100% nitrogen. The thermal annealing time can be, for example, 3 minutes to 10 minutes. Such thermal annealing is performed using, for example, a high-speed annealing furnace using radiation.

  In step S211, the insulating film 30 is removed after the annealing process. When the insulating film 30 is made of a silicon oxide film, the insulating film 30 can be removed using hydrofluoric acid. The thin insulating film 30b can suppress damage and contamination due to ion implantation when an n-type dopant is introduced into the exposed light guide layer (second region 26b) by ion implantation. The region 26c is modified into the second region 26b by the dopant activation process.

  The doped region 26c formed by ion implantation and annealing will be described with reference to FIG. In the light guide layer 25a of the light guide layer 25 (p-side light guide region), the first region 26a and the second region 26b are divided by ion implantation. The first region 26a and the second region 26b are arranged along a reference plane that intersects the normal axis of the substrate main surface 39a. A ridge structure 35 is located on the first region 26a. The second region 26b includes an n-type dopant introduced by ion implantation, and the dopant concentration is the first concentration. In the second region 26b having the ion-implanted state, the n-type dopant is activated, and when the activated n-type dopant concentration is higher than the activated p-type dopant concentration, the second region 26b is n-conductive. Have sex. Therefore, the second region 26b provides a potential barrier for the first region 26a.

  In step S212, after the insulating film 30 is removed, the insulating film 44 is deposited while leaving the mask film 24a and the sacrificial film 22a in order to form another insulator so as to embed the ridge structure. The insulating film 44a includes an insulator 44a that embeds a ridge structure, and a deposit 44b formed on the mask film 24a and the sacrificial film 22a. In FIG. 7B, although the insulator covers the side surface of the metal layer 19, in this embodiment, the insulator 44a embeds a ridge structure.

  In step S213, the insulating film 44 is lifted off using the sacrificial film 22a in the mask, the deposit 44b formed on the mask film 24a and the sacrificial film 22a is removed, and the ridge upper surface of the ridge structure is exposed. As a result of this lift-off, a substrate product SP having a ridge structure embedded with an insulator 44a is produced.

  After the annealing step, in step S214, an ohmic electrode is formed. For example, an ohmic electrode is formed to cover the ridge upper surface of the ridge structure and the upper surface of the insulator 44a. In the formation of the ohmic electrode, the metal film can be etched using photolithography after the metal film is deposited so as to cover the upper surface of the ridge and the upper surface of the insulator 44a. This etching can be performed under the conditions described above, but is not limited to this.

  In step S215, a pad electrode 45 is formed on the upper surface of the ohmic electrode and insulator 44a. In order to form the pad electrode 45, for example, a lift-off method can be used as in step S123. The pad electrode 45 can be made of, for example, Au or Ti / Pt / Au. If necessary, after the back surface 39b of the substrate 39 is polished, the back electrode 49 is formed on the polishing surface of the substrate.

  According to the method for manufacturing this nitride semiconductor laser (hereinafter referred to as “manufacturing method”), the light guide layer 25a of the light guide layer 25 is along the reference plane that intersects the normal axis of the main surface of the substrate. A first region 26a and a second region 26b are formed. The second region of the light guide layer 25a is formed to have n conductivity including an activated n-type dopant doped at a first concentration, while the first region 26a is directly under the ridge structure, Includes p-type dopants introduced during epi growth and no n-type dopants from ion implantation. Therefore, the second region 26b provides a potential barrier for the first region 26a. Carriers flowing from the ridge structure to the first region 26a are guided by the second region 26b forming a potential barrier by a pn junction. When the substrate 39 has a semipolar surface, the active layer allows long wavelength light emission. Separating optical confinement and current confinement allows adjustment of the far field image (FFP).

(Example 4)
FIG. 12 is a drawing showing an example of a nitride semiconductor laser. In the preparation step, a semipolar GaN substrate 10a is prepared. The main surface of this semipolar GaN substrate has a {20-21} plane. In the {20-21} plane, the GaN c-axis of the substrate is inclined at an angle of 75 degrees in the direction of the GaN m-axis. Crystal growth is performed by metal organic vapor phase epitaxy. In the cleaning process, thermal cleaning of the GaN substrate is performed in a growth furnace. The thermal cleaning is performed in an atmosphere containing ammonia (NH ₃ ) and hydrogen (H ₂ ), and the heat treatment temperature is 1050 degrees Celsius. After this pretreatment, in the buffer growth step, an n-type GaN layer (Si doped: 3 × 10 ¹⁸ cm ⁻³ ) having a thickness of 1000 nm is grown on the semipolar main surface of the GaN substrate. The growth temperature is 1050 degrees Celsius. In the n-type cladding process, after the substrate temperature is lowered to 840 degrees Celsius, an n-type cladding layer is grown on the n-type GaN layer. In this example, an n-type InAlGaN cladding layer (Si-doped: 3 × 10 ¹⁸ cm ⁻³ ) having a thickness of 1000 nm is grown as an n-type cladding layer. The n-type InAlGaN cladding layer has an In composition of 0.03 and an Al composition of 0.14. In the n-side light guide growth step, an n-type GaN light guide layer (Si doping: 3 × 10 ¹⁸ cm ⁻³ ) having a thickness of 200 nm is grown on the n-type InAlGaN cladding layer at a substrate temperature of 840 degrees Celsius. Next, an n-type InGaN optical guide layer (Si doped: 1 × 10 ¹⁸ cm ⁻³ ) having a thickness of 160 nm is grown so as to form a heterojunction with the n-type GaN optical guide layer. The In composition of this InGaN layer is 0.03. After forming the n-side semiconductor layer composed of these light guide layers, in the active layer growth step, an active layer is grown on the n-side light guide region. In this embodiment, an InGaN well layer is grown as the active layer at a substrate temperature of 790 degrees Celsius. The In composition of this InGaN layer is 0.255, and the thickness of the InGaN layer is 3 nm. This growth completes the production of the active layer. In the p-side light guide growth step, for example, after raising the substrate temperature to 840 degrees Celsius, an undoped InGaN light guide layer having a thickness of 30 nm is grown on the active layer. The In composition of this InGaN layer is 0.03. A p-type InGaN optical guide layer (Mg doped: 1 × 10 ¹⁸ cm ⁻³ ) having a thickness of 130 nm is grown on the undoped InGaN optical guide layer. The In composition of this InGaN layer is 0.03. A p-type GaN optical guide layer (Mg doped: 2 × 10 ¹⁸ cm ⁻³ ) having a thickness of 150 nm is grown on the p-type InGaN optical guide layer. After forming the p-side semiconductor layer composed of these light guide layers, in the p-type cladding step, a p-type AlGaN cladding layer (Mg doped: 1 × 10 ¹⁹ cm ⁻³⁾ having a thickness of 400 nm is formed on the p-side light guide region. ) Grow. The p-type AlGaN cladding layer has an Al composition of 0.05. After raising the substrate temperature to 1000 degrees Celsius, in the p-type contact process, a p-type GaN contact layer (Mg doped: 1 × 10 ²⁰ cm ⁻³ ) having a thickness of 50 nm is grown on the p-type AlGaN cladding layer. An epitaxial substrate can be manufactured by these steps.

A substrate product is then produced from the epitaxial substrate. In the ridge process, photolithography, dry etching and vapor deposition are applied to the epitaxial substrate to form a semiconductor ridge having a width of 2 μm using a mask. In this fabrication, the Group III nitride semiconductor region is etched to form a semiconductor ridge. The semiconductor ridge is processed by dry etching. In the subsequent ion implantation step, Si is implanted using this mask. This ion implantation is performed to add donors on both sides of the bottom of the semiconductor ridge. The thickness of the semiconductor modified by ion implantation is, for example, 10 to 100 nm, which is smaller than the thickness of the p-type InGaN optical guide layer. The implanted donor concentration is larger than the acceptor density of the p-type InGaN optical guide layer (for example, Mg-doped: 1 × 10 ¹⁸ cm ⁻³ ), for example, about 1E + 18 to 5E + 18 cm ⁻³ . The side and bottom surfaces of the semiconductor modified by ion implantation are surrounded by a p-type semiconductor layer and are separated from the undoped InGaN light guide layer. The energy and dose of ion implantation are determined so as to realize the above thickness and concentration.

In the protective insulating film forming step, an insulating film, for example, a silicon oxide film (specifically, SiO ₂ ) is formed. This insulating film covers the side surface of the semiconductor ridge and the surface of the light guide layer (surface formed by etching) and has an opening on the upper surface of the semiconductor ridge (contact surface showing semipolarity). An ohmic electrode (eg, Ni / Au, Pd) and a pad electrode (eg, Ti / Au) are formed on the semiconductor ridge and the insulating film. The back surface of the GaN substrate is polished to form a polished substrate having a substrate thickness of 80 μm. A cathode electrode (for example, Ti / Al) and a pad electrode (for example, Ti / Au) are formed over the entire polished surface of the GaN substrate. By these steps, a substrate product is produced.

After forming the electrodes, in the resonator forming step, the substrate product is cleaved to form a laser bar having an end surface (an end surface different from the cleaved surface) for the optical resonator. A dielectric multilayer film is formed on the end face of the laser bar. In the dielectric multilayer film process, the dielectric multilayer film is made of SiO ₂ / TiO ₂ . In the separation step, a semiconductor laser is manufactured by separating the laser bar. By these steps, a semiconductor laser is fabricated on the semipolar GaN substrate {20-21} plane inclined at an angle of 75 degrees in the m-axis direction. This semiconductor laser can emit light in the 520 nm wavelength band.

  A green semiconductor laser having a ridge structure has strong optical confinement in the horizontal direction, and is likely to be kinked (bent) in the current-output characteristics. The light confinement in the horizontal direction can be weakened by reducing the depth of the ridge. However, when the depth of the ridge is reduced, the current confinement due to the ridge is also weakened, and the threshold for laser oscillation is increased. The ridge structure has the following roles. One is to confine light in the horizontal direction. Another one constricts the current in the horizontal direction. According to the knowledge of the inventors, in a semiconductor laser that emits light having a long wavelength such as a green wavelength band, it is necessary to perform current confinement in order to reduce the threshold current, but light confinement is rather performed. Better not. When the ridge structure is embedded with an inorganic insulating film such as silicon oxide, if silicon oxide is formed on the side surface of the ridge structure, a region having a lower refractive index than the semiconductor approaches the light guide region, so that light confinement becomes strong. In order to avoid this, it is preferable to bury the ridge structure using a material (for example, aluminum nitride) different from the inorganic insulating film such as silicon oxide.

  The present invention is not limited to the specific configuration disclosed in the present embodiment.

  According to the present embodiment, a nitride semiconductor laser having a structure in which current confinement and optical confinement can be adjusted separately from each other can be provided. Further, according to the present embodiment, a method for manufacturing this nitride semiconductor laser can be provided.

DESCRIPTION OF SYMBOLS 11 ... Nitride semiconductor light emitting element, 13 ... 1st group III nitride semiconductor region, 15 ... Active layer, 17 ... 2nd group III nitride semiconductor region, 19 ... Center semiconductor region, 21 ... 1st light guide area | region 23 ... n-type cladding layer, 25 ... second light guide region, 27 ... p-type cladding layer, 29 ... p-type contact layer, Ax ... lamination axis, 31 ... core region, HJ1, HJ2, HJ3 ... semiconductor junction, 33a ... well layer, 33b ... barrier layer, 39 ... substrate, 39a ... semipolar main surface, Angle ... tilt angle, Sc ... reference plane, 26a ... p-doped region of n-type ion implantation, 26b ... p-doped region.

Claims (35)

A nitride semiconductor laser comprising:
A p-side light guide region provided on a semiconductor surface made of a group III nitride semiconductor and including a first semiconductor layer made of a first group III nitride semiconductor;
An n-side light guide region provided on the semiconductor surface and made of a Group III nitride semiconductor;
An active layer provided between the n-side light guide region and the p-side light guide region;
a ridge structure including a p-type cladding layer;
With
The n-side light guide region, the active layer, the p-side light guide region, and the ridge structure are sequentially arranged in a direction of a first axis extending in a direction intersecting the semiconductor surface to form a stacked structure,
The p-side light guide region forms a first interface in contact with the active layer,
The first semiconductor layer has a first region and a second region, and the first region and the second region are arranged along a reference plane intersecting the first axis,
The ridge structure is provided on the first region of the first semiconductor layer;
The second region of the first semiconductor layer includes an n-type dopant doped at a first concentration;
The nitride semiconductor laser, wherein the second region of the first semiconductor layer provides a potential barrier to the first region of the first semiconductor layer. The first interface is inclined with respect to a first reference plane perpendicular to a first reference axis extending in the c-axis direction made of the group III nitride semiconductor,
The nitride semiconductor laser according to claim 1, wherein the semiconductor surface exhibits semipolarity. An insulator that covers the surface of the second region of the first semiconductor layer and embeds the ridge structure in contact with a side surface of the ridge structure;
The nitride semiconductor laser according to claim 1, wherein a refractive index of the insulator is lower than a refractive index of the p-side light guide region.   The nitride semiconductor laser according to claim 3, wherein a distance between the insulator on the second region of the first semiconductor layer and the active layer is 100 nm or more.   5. The nitride semiconductor laser according to claim 3, wherein a distance between the insulator on the second region of the first semiconductor layer and the active layer is 300 nm or less. The first semiconductor layer is made of In _U1 Ga _1-U1 N,
6. The nitride semiconductor laser according to claim 1, wherein an indium composition U <b> 1 of the first semiconductor layer is 0.02 or more and 0.05 or less.   The nitride semiconductor laser according to claim 6, wherein a composition U1 of indium in the first semiconductor layer is 0.04 or less. Further comprising a substrate having a main surface made of a hexagonal group III nitride semiconductor,
The n-side light guide region, the active layer, the p-side light guide region, and the p-type cladding layer are sequentially arranged on the main surface of the substrate,
The principal surface of the substrate is c-axis of the hexagonal group III nitride semiconductor from a second reference plane orthogonal to a second reference axis extending in the c-axis direction of the hexagonal group III nitride semiconductor. The nitride according to any one of claims 1 to 6, wherein the nitride is tilted at an angle in the range of 10 degrees to less than 80 degrees in the m-axis direction of the hexagonal group III nitride semiconductor. Semiconductor laser.   The nitride semiconductor laser according to any one of claims 1 to 8, wherein the active layer has a single quantum well structure or a multiple quantum well structure.   10. The nitride semiconductor laser according to claim 1, wherein an oscillation wavelength of the active layer is in a range of 480 nm or more and 550 nm or less.   11. The nitride semiconductor laser according to claim 1, wherein an oscillation wavelength of the active layer is in a range from 510 nm to 540 nm. The second region of the first semiconductor layer exhibits n-type conductivity;
11. The nitride semiconductor laser according to claim 1, wherein in the first semiconductor layer, the first region forms a pn junction with the second region.   11. The n-type dopant is not activated, and in the first semiconductor layer, the first region forms a pi junction with the second region. 11. Nitride semiconductor laser.   The nitride semiconductor laser according to claim 12 or 13, wherein the n-type dopant in the second region of the first semiconductor layer is introduced by ion implantation.   The nitride semiconductor laser according to claim 1, wherein the first region and the second region of the first semiconductor layer include a p-type dopant. The second region of the first semiconductor layer includes a second concentration of p-type dopant;
The nitride semiconductor laser according to claim 1, wherein the first concentration is higher than the second concentration in the second region of the first semiconductor layer.   The semiconductor surface extends from the c-axis of the group III nitride semiconductor to the first reference plane perpendicular to the first reference axis extending in the c-axis direction made of the group III nitride semiconductor. The nitride semiconductor laser according to claim 1, wherein the nitride semiconductor laser is inclined at an angle in a range of not less than 63 degrees and not more than 80 degrees in the axial direction.   The nitride semiconductor laser according to claim 1, further comprising an electrode in contact with an upper surface of the ridge structure. The p-type cladding layer _{is In X1 Al Y1 Ga 1-X1} -Y1 N (0 ≦ X1 <0.05,0 ≦ Y1 <0.20),
The _{In X1 Al Y1 Ga 1-X1} -Y1 N has a larger band gap than the band gap profile of the p-side optical guiding region, the nitride according to any one of claims 1 to 16 semiconductor laser. The p-side light guide region includes an undoped In _{U2Ga1 -U2N} layer,
The nitride semiconductor laser according to any one of claims 1 to 19, wherein the In _{U2Ga1 -U2N} layer is provided between the active layer and the first semiconductor layer. The ridge structure further includes a p-type GaN layer provided between the first region of the first semiconductor layer of the p-side light guide region and the p-type cladding layer,
The p-type cladding layer is in contact with the p-type GaN layer;
The first semiconductor layer is in contact with the p-type GaN layer;
The active layer is in contact with the p-side light guide region;
The nitride semiconductor laser according to any one of claims 1 to 20, wherein the p-side light guide region includes the p-type GaN layer. A method for fabricating a nitride semiconductor laser comprising:
preparing an epitaxial substrate including an epitaxial structure including an n-side light guide region, an active layer, and a p-side light guide region, and a p-doped semiconductor region;
Forming a mask for a ridge structure on the p-doped semiconductor region of the epitaxial substrate;
Etching the p-doped semiconductor region and the p-side light guide region using the mask to form an etched p-side light guide region and a ridge structure;
Performing ion implantation of an n-type dopant into the etched p-side light guide region after forming the ridge structure;
With
The n-side light guide region, the active layer, the p-side light guide region, and the ridge structure are sequentially arranged in the direction of the first axis on the semiconductor surface made of a group III nitride semiconductor to form a stacked structure,
The p-side light guide region includes a first semiconductor layer, and the first semiconductor layer has a first region and a second region, and the first region and the second region intersect with the first axis. Arranged along the plane,
The ridge structure is provided on the first region of the first semiconductor layer;
The second region of the first semiconductor layer includes an n-type dopant introduced at a first concentration by the ion implantation;
A method of fabricating a nitride semiconductor laser, wherein the second region of the first semiconductor layer provides a potential barrier to the first region of the first semiconductor layer. The p-side light guide region forms a first interface in contact with the active layer,
The first interface is inclined with respect to a first reference plane orthogonal to a first axis extending in the c-axis direction made of the group III nitride semiconductor,
23. The method of fabricating a nitride semiconductor laser according to claim 22, wherein the semiconductor surface exhibits semipolarity. A step of growing an insulating film on the surface of the second region of the first semiconductor layer and on the ridge structure;
The method for producing a nitride semiconductor laser according to claim 22 or 23, wherein the ion implantation is performed through the insulating film.   The method for producing a nitride semiconductor laser according to any one of claims 22 to 24, wherein the first region and the second region of the first semiconductor layer include a p-type dopant.   The method for producing a nitride semiconductor laser according to any one of claims 22 to 25, wherein an oscillation wavelength of the active layer is in a range of 480 nm to 550 nm.   27. The method for producing a nitride semiconductor laser according to any one of claims 22 to 26, wherein an oscillation wavelength of the active layer is in a range from 510 nm to 540 nm.   The method for producing a nitride semiconductor laser according to any one of claims 22 to 27, further comprising a step of performing an annealing process for activating the n-type dopant after performing the ion implantation. . Forming an insulator for embedding the ridge structure after the annealing treatment;
Forming an electrode in contact with the top surface of the ridge structure after forming the insulator;
The method for producing a nitride semiconductor laser according to claim 28, further comprising: The second region of the first semiconductor layer exhibits n-type conductivity;
30. The method for producing a nitride semiconductor laser according to claim 22, wherein, in the first semiconductor layer, the first region forms a pn junction with the second region. Forming an insulator filling the ridge structure after the ion implantation;
Forming an ohmic electrode in contact with the top surface of the ridge structure after forming the insulator;
The method for producing a nitride semiconductor laser according to any one of claims 22 to 30, further comprising: Before preparing the mask after preparing the epitaxial substrate, further comprising forming a metal film on the epitaxial substrate,
The mask is formed on the metal film;
28. The method for producing a nitride semiconductor laser according to claim 22, wherein the metal film is etched using the mask.   The n-type dopant is not activated, and in the first semiconductor layer, the first region forms a pi junction with the second region, according to any one of claims 22 to 27, and 32. A method for producing the nitride semiconductor laser according to claim 1.   The method for producing a nitride semiconductor laser according to claim 22, wherein the first region and the second region of the first semiconductor layer contain a p-type dopant. The second region of the first semiconductor layer includes a second concentration of p-type dopant;
35. The method for producing a nitride semiconductor laser according to claim 22, wherein the first concentration is higher than the second concentration in the second region of the first semiconductor layer.

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