JP5626279B2 - Group III nitride semiconductor laser device and method for manufacturing group III nitride semiconductor laser device - Google Patents

Description

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

  Patent Document 1 describes a nitride semiconductor laser device, and this nitride semiconductor laser device generates light having a wavelength of 430 nm or more. The nitride semiconductor laser device can improve characteristics such as a reduction in operating voltage, an increase in external quantum efficiency, and a reduction in oscillation threshold current density.

JP 2010-129676 A

  The nitride semiconductor laser element of Patent Document 1 includes an n-type AlGaN cladding layer, a GaN layer, a first InGaN light guide layer, a light emitting layer, a second InGaN light guide layer, a nitride semiconductor intermediate layer, a p-type AlGaN layer, And a p-type AlGaN cladding layer, which are provided on the nitride semiconductor substrate in this order. The n-type AlGaN cladding layer has an Al composition ratio of 3% to 5% and a thickness of 1.8 μm to 2.5 μm, and the first and second InGaN light guide layers are 3% to 6%. In composition ratio. The thickness of the first light guide layer is 120 nm or more and 160 nm or less. The p-type AlGaN layer is in contact with the p-type AlGaN cladding layer, and its Al composition ratio is higher than that of the p-type cladding layer and is 10% or more and 35% or less.

  In a nitride semiconductor laser element having a ridge structure, the width of the optical waveguide can be reduced by reducing the width of the ridge structure in order to reduce the threshold current. Reducing the width of the optical waveguide is effective for increasing the current confinement capability. However, when the optical waveguide width is narrowed, not only current confinement but also light confinement becomes strong. Excessive light confinement may cause the laser mode to become unstable or increase the spread angle (FFP) of the emitted laser light. Therefore, in the fabrication of a nitride semiconductor laser device, changing the optical waveguide width affects some characteristics of the semiconductor laser device, and is not a device structure that can be changed independently for current confinement. Similarly, in the nitride semiconductor laser device, by increasing the width of the ridge structure and / or making the bottom of the ridge structure shallow (decreasing the etching digging amount in the ridge formation), The spread angle of FFP can be controlled. However, as can be understood from the above description, the current confinement capability of the semiconductor laser device changes regardless of the method of increasing the width of the ridge structure or shallowing the bottom of the ridge structure.

  An object of the present invention is to provide a group III nitride semiconductor laser device having a structure that makes it possible to bring the characteristics of the semiconductor laser device close to desired current confinement properties and desired optical confinement properties. It is an object of the present invention to provide a method for manufacturing a nitride semiconductor laser device.

  A group III nitride semiconductor laser device according to the present invention includes (a) a first group III nitride semiconductor region having a semipolar plane made of a hexagonal group III nitride semiconductor, and (b) the first group III nitride. An active layer provided on the semipolar surface of the semiconductor region; and (c) a second group III nitride semiconductor region provided on the semipolar surface of the first group III nitride semiconductor region. The active layer is provided between the first group III nitride semiconductor region and the second group III nitride semiconductor region, and an oscillation wavelength of the active layer is in a range of not less than 400 nm and not more than 550 nm, and the first group III nitride The semiconductor region includes a first cladding layer made of a group III nitride semiconductor of a first conductivity type and a first light guide layer, and the first light guide layer is made of a gallium nitride semiconductor containing indium as a group III constituent element. The second group III nitride semiconductor region includes a second cladding layer made of a second conductivity type group III nitride semiconductor and a second light guide layer, and the thickness of the second light guide layer is The first light guide layer is thinner than the first light guide layer, the thickness of the first light guide layer is 370 nm or more, and the second group III nitride semiconductor region has a ridge structure.

  According to this group III nitride semiconductor laser device, the second group III nitride semiconductor region has a ridge structure, and the ridge structure can confine a current to the active layer according to the width of the group III nitride semiconductor region. It also affects optical confinement in the group nitride semiconductor region. The thickness of the second light guide layer in the group III nitride semiconductor laser device is smaller than the thickness of the first light guide layer, and the thickness of the first light guide layer in the group III nitride semiconductor region is 370 nm or more. Have. Therefore, the influence caused by the width of the ridge structure can be reduced with respect to the optical confinement characteristics in the group III nitride semiconductor laser device. The current confinement of the group III nitride semiconductor laser device is achieved mainly depending on the width of the ridge structure. Moreover, the light confinement depends on the thick first light guide layer in addition to the ridge structure.

  In the group III nitride semiconductor laser device according to the present invention, the first light guide layer preferably has a thickness of 550 nm or less.

  According to this group III nitride semiconductor laser device, the first light guide layer having a thickness of more than 550 nm may increase the threshold current.

  In the group III nitride semiconductor laser device according to the present invention, the normal line of the semipolar plane of the first group III nitride semiconductor region is in the c-axis of the group III nitride semiconductor of the first group III nitride semiconductor region. An inclination is formed with respect to the inclination, and an inclination angle of the inclination may be in a range of 10 degrees to 80 degrees.

  According to this group III nitride semiconductor laser device, when the inclination of the c-axis of the group III nitride semiconductor is less than 10 degrees, the group III nitride semiconductor exhibits a property close to a polar plane. When the inclination of the c-axis of the group III nitride semiconductor exceeds 80 degrees, the group III nitride semiconductor exhibits a property close to a nonpolar plane.

  In the group III nitride semiconductor laser device according to the present invention, it is preferable that a bottom of the ridge structure is located in the second light guide layer in the second group III nitride semiconductor region.

  According to the group III nitride semiconductor laser device, when the bottom of the ridge structure is located in the second light guide layer in the second group III nitride semiconductor region, the current in the second group III nitride semiconductor region is You can guide near and control the spread of current.

  In the group III nitride semiconductor laser device according to the present invention, the distance between the bottom of the ridge structure and the active layer is preferably 150 nm or less.

  According to this group III nitride semiconductor laser device, when the distance between the bottom of the ridge structure and the active layer is 150 nm or less, the width of the ridge structure contributes not only to current confinement but also to light confinement.

  In the group III nitride semiconductor laser device 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 group III nitride semiconductor laser device, a laser beam having a relatively long wavelength can be provided.

  In the group III nitride semiconductor laser device according to the present invention, the oscillation wavelength of the active layer is preferably in the range of 510 nm or more and 540 nm or less.

  According to this group III nitride semiconductor laser device, a long wavelength laser beam can be provided. Due to 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. Further, since the ridge structure contributes to both current confinement and optical confinement, the thick first light guide layer in the group III nitride semiconductor region can be used in the group III nitride semiconductor laser device without greatly changing the current confinement. Light confinement can be easily adjusted.

  In the group III nitride semiconductor laser device according to the present invention, the ridge structure includes a normal line of the semipolar plane of the first group III nitride semiconductor region and the group III nitride of the first group III nitride semiconductor region. It can extend along the mn plane defined by the m-axis of the semiconductor.

  According to this group III nitride semiconductor laser device, when the ridge structure 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 ridge structure but also to the reduction of the threshold current.

  In the group III nitride semiconductor laser device according to the present invention, the first light guide layer may be made of ternary InGaN, and the active layer may include a ternary InGaN layer.

  According to this group III nitride semiconductor laser device, the first light guide layer made of ternary InGaN is suitable for an active layer including a ternary InGaN layer.

  In the group III nitride semiconductor laser device according to the present invention, the active layer includes an InGaN well layer, and the indium composition of the first light guide layer is smaller than the indium composition of the InGaN well layer, and the first light guide layer The indium composition may be 2% or more.

  According to this group III nitride semiconductor laser device, the first light guide layer having an indium composition of 2% or more can provide a refractive index difference with respect to the semiconductor layer provided between the first light guide layer and the substrate.

  In the group III nitride semiconductor laser device according to the present invention, the active layer includes an InGaN well layer, the indium composition of the first light guide layer is 6% or less, and is smaller than the indium composition of the InGaN well layer. That is good.

  According to this group III nitride semiconductor laser device, the first light guide layer having an indium composition of 6% or less is a semiconductor provided between the first light guide layer and the substrate with respect to the light propagating through the laser waveguide. A refractive index between the layer and the active layer can be provided.

  In the group III nitride semiconductor laser device according to the present invention, the first group III nitride semiconductor region further includes a third light guide layer, and the third light guide layer includes a material different from InGaN, and The guide layer may be provided between the first light guide layer and the first cladding layer, and the thickness of the first light guide layer may be greater than the thickness of the third light guide layer.

  According to this group III nitride semiconductor laser device, the first group III nitride semiconductor region can include a plurality of light guide layers.

  The group III nitride semiconductor laser device according to the present invention may further include an ohmic electrode provided on the upper surface of the ridge structure. The second group III nitride semiconductor region further includes a contact layer made of a second conductivity type group III nitride semiconductor, and the second cladding layer is provided between the contact layer and the second light guide layer. The ohmic electrode may be in contact with the contact layer.

  According to this group III nitride semiconductor laser device, the ohmic electrode makes contact with the contact layer on the upper surface of the ridge structure, so that carriers from the ohmic electrode can be confined according to the width of the ridge structure.

  In the group III nitride semiconductor laser device according to the present invention, the ohmic electrode preferably includes palladium.

  According to this group III nitride semiconductor laser device, palladium can provide good contact with the group III nitride semiconductor of the contact layer.

  The group III nitride semiconductor laser device according to the present invention has an opening that matches the upper surface of the ridge structure, covers a surface of the first group III nitride semiconductor region, covers an upper surface of the ohmic electrode, and And a pad electrode provided on the protective film. The protective film covers a side surface of the ridge structure, and the refractive index of the protective film is smaller than the refractive index of the second group III nitride semiconductor region, and the ohmic electrode passes through the opening of the protective film. Contact is made with the Group III nitride semiconductor region.

  According to this group III nitride semiconductor laser device, since the refractive index of the protective film is smaller than the refractive index of the second group III nitride semiconductor region, the protective film covering the side surface of the ridge structure is related to light confinement.

  The group III nitride semiconductor laser device according to the present invention may further include a substrate having a semipolar main surface made of a hexagonal group III nitride. The first group III nitride semiconductor region, the active layer, and the second group III nitride semiconductor region are disposed in a normal direction of the semipolar main surface of the substrate.

  In the group III nitride semiconductor laser device according to the present invention, the normal line of the semipolar main surface of the substrate forms an inclination with respect to the c-axis of the group III nitride semiconductor of the substrate, and the inclination of the inclination The angle is preferably in the range of 63 degrees to 80 degrees.

  According to this group III nitride semiconductor laser device, a substrate having a c-axis tilt in the range of not less than 63 degrees and not more than 80 degrees can provide a plane orientation suitable for producing an active layer suitable for long-wavelength laser oscillation. 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 device according to the present invention, the substrate may include a hexagonal conductive group III nitride which is any one of GaN, InGaN, AlGaN, and InAlGaN.

  According to this group III nitride semiconductor laser device, a substrate made of any one of GaN, InGaN, AlGaN, and InAlGaN can be used.

In group III nitride semiconductor laser device according to the present invention, the first cladding layer is of n conductivity _{In X1 Al Y1 Ga 1-X1} -Y1 N (0 <X1 <0.05,0 <Y1 <0. 20).

  According to this group III nitride semiconductor laser device, the first cladding layer can provide good optical confinement with respect to the light guide layer.

In group III nitride semiconductor laser device according to the present invention, the second cladding layer is of p conductivity _{In X2 Al Y2 Ga 1-X2} -Y2 N (0 <X2 <0.05,0 <Y2 <0. 20).

  According to this group III nitride semiconductor laser device, the second cladding layer can provide good optical confinement with respect to the light guide layer.

  The method of manufacturing a group III nitride semiconductor laser device according to the present invention includes: (a) a step of growing a first cladding layer made of a hexagonal group III nitride semiconductor and having a semipolar plane; A step of growing a first light guide layer on the semipolar surface of the first cladding layer, and (c) a step of forming an active layer of a gallium nitride based semiconductor after the growth of the first light guide layer; d) forming a second group III nitride semiconductor region having a ridge structure after the growth of the active layer. The oscillation wavelength of the active layer is 400 nm or more and 550 nm or less, which is thinner than the thickness of the first light guide layer, and the thickness of the first light guide layer is 370 nm or more.

  In the manufacturing method according to the present invention, the film thickness of the first light guide layer is preferably 550 nm or less. According to this manufacturing method, the first light guide layer having a film thickness exceeding 550 nm may lead to an increase in threshold current.

  In the manufacturing method according to the present invention, the normal line of the semipolar plane of the first group III nitride semiconductor region is inclined with respect to the c-axis of the group III nitride semiconductor of the first group III nitride semiconductor region. The inclination angle of the inclination may be in the range of 10 degrees to 80 degrees. According to this manufacturing method, when the inclination of the c-axis of the group III nitride semiconductor is less than 10 degrees, the group III nitride semiconductor exhibits a property close to a polar plane. When the inclination of the c-axis of the group III nitride semiconductor exceeds 80 degrees, the group III nitride semiconductor exhibits a property close to a nonpolar plane.

  In the manufacturing method according to the present invention, it is preferable that a bottom of the ridge structure is located in the second light guide layer in the second group III nitride semiconductor region. According to this manufacturing method, when the bottom of the ridge structure is located in the second optical guide layer in the second group III nitride semiconductor region, the current in the second group III nitride semiconductor region is guided to the vicinity of the active layer. , Current spreading can be controlled.

  In the manufacturing method according to the present invention, the distance between the bottom of the ridge structure and the active layer is preferably 150 nm or less. According to this manufacturing method, when the distance between the bottom of the ridge structure and the active layer is 150 nm or less, the width of the ridge structure contributes not only to current confinement but also to light confinement.

  A method of manufacturing a group III nitride semiconductor laser device according to the present invention includes: (a) preparing a plurality of substrates having a principal surface made of hexagonal group III nitride; and (b) a first cladding layer. And a first group III nitride semiconductor region having a first light guide layer, an active layer made of a gallium nitride-based semiconductor, and a second layer III nitride semiconductor region having a second cladding layer and a second light guide layer A plurality of trial epitaxial substrates having different thicknesses of the first light guide layer, and (c) a ridge structure on the plurality of trial epitaxial substrates. Forming a plurality of trial substrate products, and (d) evaluating a far-field image of the plurality of trial substrate products, the far-field image and the first light. The relationship with the thickness of the guide layer (E) determining the thickness of the first light guide layer for the gallium nitride based semiconductor laser device using the result of the evaluation; and (f) the first light guide layer is And a step of producing an epitaxial substrate for the gallium nitride based semiconductor laser device so as to have the determined thickness.

  According to this method of manufacturing a gallium nitride based semiconductor laser device, a group III nitride semiconductor laser device having a structure that makes it possible to bring the characteristics of the semiconductor laser device close to a desired optical confinement property can be provided.

  In the manufacturing method according to the present invention, the normal line of the semipolar plane of the first group III nitride semiconductor region is inclined with respect to the c-axis of the group III nitride semiconductor of the first group III nitride semiconductor region. The inclination angle of the inclination may be in the range of 10 degrees to 80 degrees. According to this manufacturing method, when the inclination of the c-axis of the group III nitride semiconductor is less than 10 degrees, the group III nitride semiconductor exhibits a property close to a polar plane. When the inclination of the c-axis of the group III nitride semiconductor exceeds 80 degrees, the group III nitride semiconductor exhibits a property close to a nonpolar plane.

  In the manufacturing method according to the present invention, it is preferable that a bottom of the ridge structure is located in the second light guide layer in the second group III nitride semiconductor region. According to this manufacturing method, when the bottom of the ridge structure is located in the second optical guide layer in the second group III nitride semiconductor region, the current in the second group III nitride semiconductor region is guided to the vicinity of the active layer. , Current spreading can be controlled.

  In the manufacturing method according to the present invention, the distance between the bottom of the ridge structure and the active layer is preferably 150 nm or less. According to this manufacturing method, when the distance between the bottom of the ridge structure and the active layer is 150 nm or less, the width of the ridge structure contributes not only to current confinement but also to light confinement.

  In the manufacturing method according to the present invention, the threshold current for laser oscillation of the plurality of trial substrate products is evaluated, and the relationship between the threshold current and the thickness of the first light guide layer is determined. The process of obtaining can be further provided. In the step of determining the thickness of the first light guide layer, the thickness of the first light guide layer is determined using the evaluation result of the far-field image and the evaluation result of the threshold current. be able to.

  According to this method of manufacturing a gallium nitride based semiconductor laser device, a group III nitride semiconductor laser device having a structure that makes it possible to bring the characteristics of the semiconductor laser device close to desired current confinement properties and desired optical confinement properties. Can be provided.

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

  As described above, according to the present invention, it is possible to provide a group III nitride semiconductor laser device having a structure that makes it possible to bring the characteristics of the semiconductor laser device closer to desired current confinement properties and desired optical confinement properties, In addition, a method for producing this group III nitride semiconductor laser device can be provided.

FIG. 1 is a view showing a structure according to a nitride semiconductor light emitting device according to the present embodiment. FIG. 2 is a drawing for explaining the relationship between the ridge structure and the optical confinement layer. FIG. 3 is a drawing showing a group III nitride semiconductor laser device fabricated in the example. FIG. 4 is a drawing schematically showing main steps in the method of manufacturing the nitride semiconductor laser device according to the present embodiment. FIG. 5 is a drawing schematically showing main steps in the method of manufacturing the nitride semiconductor laser element according to the present embodiment. FIG. 6 is a drawing schematically showing main steps in the method of manufacturing the nitride semiconductor laser element according to the present embodiment. FIG. 7 is a drawing showing a laser structure according to this embodiment. FIG. 8 shows the FFP divergence angle and the threshold current density in the laser structure according to this example. FIG. 9 is a diagram showing simulation results. FIG. 10 is a drawing showing a main process flow in the method of manufacturing the group III nitride semiconductor laser device according to the present embodiment. FIG. 11 is a drawing showing a main process flow in the method for manufacturing the nitride semiconductor light emitting device according to the present embodiment.

  DESCRIPTION OF EMBODIMENTS Embodiments of the present invention relating to a group III nitride semiconductor laser device and a method for manufacturing a group III nitride semiconductor laser device 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 view showing a structure according to a nitride semiconductor light emitting device according to the present embodiment. 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 group III nitride semiconductor laser device 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 semipolar surface 13a made of a hexagonal group III nitride semiconductor. The active layer 15 is provided on the semipolar surface 13 a of the first group III nitride semiconductor region 13. The second group III nitride semiconductor region 17 is provided on the semipolar surface 13 a of the first group III nitride semiconductor region 13. 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. 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 method 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 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. 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 27 includes a second light guide layer 25a, and includes a gallium nitride semiconductor including indium as a group III constituent element. 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 25c.

  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.

  Another light guide layer 25 includes a fourth light guide layer 25b in addition to the second light guide layer 25a. The second light guide layer 25 a is located between the fourth light guide layer 25 b and the active layer 15 and is in contact with the active layer 15. The fourth light guide layer 25b is made of a semiconductor different from the semiconductor material of the second light guide layer 25a, and the band gap of the fourth light guide layer 25b is larger than the band gap of the second light guide layer 25a.

  In one embodiment, the thickness of the light guide layer 21 is greater than the thickness of the light guide layer 25. The thickness of the second light guide layer 25a is thinner than the thickness of the first light guide layer 21a. The thickness of the first light guide layer 21a is preferably 370 nm or more.

  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 active layer 15 and the light guide layer 21 constitute a first junction HJ1. The n-type cladding layer 23 is made of a group III nitride semiconductor, and the first junction HJ1 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. It inclines at the inclination angle Angle. In FIG. 1, the reference plane in the n-type cladding layer 23 is substantially orthogonal to an axis (axis indicated by the vector VC) indicating the direction of the c-axis of the crystal coordinate system CR. The active layer 15 and the light guide layer 25 constitute a second junction HJ2. The second junction HJ2 is inclined at an inclination angle Angle greater 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.

  The semiconductor ridge 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 semiconductor ridge 35. The semiconductor ridge 35 has an upper end TOP and a bottom BOTTOM. The upper surface 35 a of the semiconductor ridge 35 forms a junction J 0 with the electrode 19. A distance D between the bottom BOTTOM of the semiconductor ridge 35 and the upper surface 15a of the active layer 15 may be 150 nm or less. This is because if it is larger than this, the current confining ability by the ridge becomes insufficient. The distance D can be 20 nm or more. If it is smaller than this, the active layer is damaged and deteriorated by the RIE process at the time of ridge formation.

  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 semiconductor ridge 35 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 semiconductor light emitting device 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 this group III nitride semiconductor laser device 11, the second group III nitride semiconductor region 17 has the ridge structure 35, and the ridge structure 35 can confine current to the active layer 15 according to its width. In addition, the optical confinement in the group III nitride semiconductor region 17 is affected. The thickness of the first light guide layer 21a in the group III nitride semiconductor laser device 11 is larger than the thickness of the second light guide layer 25a, and the first light guide layer 21a in the group III nitride semiconductor region 13 is 370 nm. It has the above thickness. Therefore, the influence caused by the width of the ridge structure 35 can be reduced with respect to the optical confinement characteristics in the group III nitride semiconductor laser device 11. The current confinement of the group III nitride semiconductor laser device 11 is achieved mainly according to the width WR of the ridge structure 35. The light confinement depends on the thick first light guide layer 21 a in addition to the ridge structure 35.

  FIG. 2 is a drawing for explaining the relationship between the ridge structure and the optical confinement layer. In order to reduce the threshold current of the group III nitride semiconductor laser device, the width of the laser waveguide extending between the cavity end faces is reduced to the width of the ridge structure as shown in FIG. It is effective to narrow the current confinement capability. However, waveguide widths that are too narrow also increase light confinement. Then, for example, the following practical problems may occur: the laser oscillation mode becomes unstable; the divergence angle of the emitted laser, that is, the far field pattern (FFP) increases. This is because the width of the waveguide is widened by adjusting the width of the ridge structure and / or the amount of ridge digging is reduced by adjusting the depth of the ridge structure, and the FFP spread in the lateral direction. It means that the corner can be controlled. For example, as shown in part (a) of FIG. 2, the spread of the propagation light of the laser waveguide is shown in part (b) of FIG. 2 by reducing the digging amount by adjusting the depth of the ridge structure. Changed from the spread in the ridge structure. However, this method deteriorates the current confinement capability, which worsens the threshold current.

  On the other hand, in the group III nitride semiconductor laser device according to the present embodiment, lateral light confinement can be adjusted independently of the current confinement capability. While maintaining the digging amount in the ridge structure, the light distribution is shifted to the n side as a whole. The amount of digging is defined as the thickness of the semiconductor layer in the digging portion that defines the ridge structure on the active layer, for example (symbol D in FIG. 1). The ridge structure of this semiconductor laser is formed in the p-side semiconductor region. Therefore, no structure for confining light in the lateral direction is provided on the n-side. The width (BOTTOM) of the ridge structure is, for example, in the range from 1.2 μm to 10 μm.

  Therefore, as shown in FIG. 2C, the thickness of the n-side light guide layer is adjusted so that the spread of the propagation light in the laser waveguide is shifted from the p-side to the n-side. In order to prevent the spread of the propagation light of the laser waveguide from deviating from the active layer, light is drawn out to the n-side semiconductor region to weaken the lateral confinement of the light.

  In order to shift the light intensity amplitude profile in the laser waveguide (profile in the vertical axis direction) to the n-side semiconductor, the thickness of the ternary InGaN light guide layer provided between the active layer and the substrate is increased. According to the inventor's knowledge, the thickness of the InGaN light guide layer is much greater than the initial prediction.

  In the group III nitride semiconductor laser device 11, the bottom BOTTOM of the ridge structure 35 is preferably located in the light guide layer 25 in the second group III nitride semiconductor region 17. When the bottom BOTTOM of the ridge structure 35 is located in the light guide layer 25 in the second group III nitride semiconductor region 17, the current in the second group III nitride semiconductor region 17 is guided to the vicinity of the active layer 15 to You can control the spread.

  The distance D between the bottom BOTTOM of the ridge structure 35 and the active layer 15 is preferably 150 nm or less. In the range of this value, the width of the ridge structure 35 has a relatively large influence on not only current confinement but also light confinement.

  When the distance D between the bottom BOTTOM of the ridge structure 35 and the active layer 15 is 20 nm or more, the current in the group III nitride semiconductor region 17 can be guided to the vicinity of the active layer 15 and the group III nitride semiconductor region The remaining film having a thickness D of 17 can protect the active layer 15.

  With reference to FIG. 1 again, the group III nitride semiconductor laser device 11 according to the present embodiment will be described. The nitride semiconductor light emitting device 11 can further include a substrate 39. The substrate 39 has a semipolar main surface 39a and a back surface 39b made of a group III nitride semiconductor. This semipolar main surface 39a is inclined with respect to a reference plane Sc orthogonal to an axis (axis Cx indicated by vector VC) extending in the c-axis direction of the group III nitride semiconductor. An angle formed by the semipolar main surface 39a and the reference surface Sc (an angle substantially equal to the angle ANGLE) can be in the range of 10 degrees to 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. In the group III nitride semiconductor layer epitaxially grown on the substrate 39, the surface of each semiconductor layer 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.

  The group III nitride semiconductor laser device 11 includes an electrode 41 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 device 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 makes it possible to grow homogeneous In incorporation and high In composition gallium nitride semiconductors. 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 device 11, the substrate 39 having the c-axis inclination in the range of not less than 63 degrees and not more than 80 degrees has a plane orientation suitable for the production of the active layer 15 suitable for long-wavelength laser oscillation. Can be provided. 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 device 11, the thickness of the first light guide layer 21a is preferably 370 nm or more and 550 nm or less. The light guide layer 21a having a thickness of more than 550 nm may increase the threshold current.

  In the group III nitride semiconductor laser device 11, the normal line 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 inclination of the c-axis of the group III nitride is 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. According to this group III nitride semiconductor laser device 11, a laser beam having a relatively long wavelength can be provided. 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 this group III nitride semiconductor laser device 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. Further, since the ridge structure 35 contributes to both current confinement and optical confinement, the thick light guide layer 21a of the first group III nitride semiconductor region 13 can be used for the group III nitride semiconductor laser device without greatly changing the current confinement. 11 can easily adjust light confinement and current confinement.

  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 6% 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 group III nitride semiconductor laser device 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 film 43 and a pad electrode 45. The protective 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.

Example 1
In this embodiment, the group III nitride semiconductor laser device 11a shown in FIG. 3 is produced. First, as shown in FIG. 4A, an epitaxial substrate E is prepared. A semipolar GaN substrate (for example, a wafer-like substrate) is prepared. The main surface of the semipolar GaN substrate has, for example, 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 with respect to the normal of the substrate main surface. Perform thermal cleaning of the GaN substrate. 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, first, a first group III nitride semiconductor region is grown. An n-type GaN layer is grown on the semipolar main surface of the GaN substrate. The thickness of the n-type GaN layer is, for example, 1100 nm. The growth temperature is 1050 degrees Celsius. After lowering the substrate temperature 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 having a thickness of 1200 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. A GaN light guide layer is grown on the n-type InAlGaN cladding layer at a substrate temperature of 840 degrees Celsius. The GaN light guide layer is n-type and has a thickness of 200 nm. An InGaN light guide layer is grown on the GaN light guide layer. The InGaN light guide layer is n-type or undoped, and its thickness is 400 nm. The In composition of this InGaN layer is, for example, 0.025. After forming the n-side inner semiconductor layer made of these light guide layers, an active layer is grown on the inner semiconductor layer. In this embodiment, an InGaN 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, for example, and the thickness of the InGaN layer is 3 nm. A Group III nitride semiconductor region is grown on the active layer. For example, after raising the substrate temperature to 840 degrees Celsius, an undoped light guide layer is grown on the active layer. The undoped light guide layer can be made of GaN and / or InGaN. The In composition of the InGaN optical guide layer is, for example, 0.025. A p-type GaN light guide layer is grown on the undoped light guide layer. After forming the p-side inner semiconductor layer made of these light guide layers, a p-type AlGaN cladding layer having a thickness of 400 nm is grown on the inner semiconductor layer. The Al composition of this p-type AlGaN cladding layer is 0.04. After raising the substrate temperature to 1000 degrees Celsius, a p-type GaN contact layer having a thickness of 50 nm is grown on the p-type AlGaN cladding layer. The epitaxial substrate E can be manufactured through these steps. In the epitaxial substrate E, the thickness TN of the n-side light guide layer is larger than the thickness TP of the p-side light guide layer.

  Photolithography, dry etching, and vacuum deposition are applied to the epitaxial substrate to fabricate a ridge-type gallium nitride semiconductor laser having a semiconductor ridge with a width of 2 μm and an optical resonator with a length of 600 μm.

In this production, a metal layer stack is formed on the epitaxial substrate E as shown in FIG. In the formation of the stacked layers, an Al film is deposited on the epitaxial substrate E, and a Ti film is deposited on the Al film. The film thickness of the Al film is, for example, 100 nm, and the film thickness of the Ti film is, for example, 10 nm. Next, as shown in FIG. 4C, after forming a stack of metal layers, an insulating film OX (for example, a silicon oxide film having a thickness of 200 nm) is grown on the epitaxial substrate E by the CVD method. As shown in FIG. 4D, for example, a mask M1 having a pattern defining a ridge shape is formed on the inorganic insulating film. In this embodiment, the mask M1 is made of a resist. Using this resist mask M1, as shown in FIG. 4E, the insulating film OX and the metal multilayer MTL are etched to form a multilayer body having a ridge pattern. As the etching, ICP dry etching can be performed, and an etchant of CHF gas is used for the silicon oxide, and an etchant of Cl ₂ gas is used for the metal stack. The stacked body manufactured by etching includes an insulating layer OX having a ridge pattern and a metal stacked layer MTL. As shown in part (f) of FIG. 4, the resist mask is removed to expose the insulating layer, thereby completing the composite mask. The composite mask includes an insulating layer OX having a ridge pattern and a metal multilayer MTL. The uppermost layer of the composite mask is made of the insulating layer OX.

  As shown in FIG. 5A, the epitaxial substrate E is etched using the composite mask. As the etching, ICP dry etching can be performed, and an etchant of Cl 2 gas is used for the nitride. The bottom of the ridge structure reaches the light guide layer on the p side. After the nitride etching, as shown in FIG. 5B, side etching is performed on the Al layer in the metal multilayer MTL. As this etching, ICP dry etching can be performed, and an etchant of Cl 2 gas is used for aluminum. As shown in FIG. 5C, after the side etching, a silicon-based inorganic insulating film SIO (for example, a silicon oxide film having a thickness of 300 nm) for a protective film is deposited prior to lift-off. As shown in FIG. 5D, after the silicon-based inorganic insulating film SIO is manufactured, lift-off is performed to expose the upper surface of the ridge structure. After removing the lift-off mask, as shown in FIG. 5E, an electrode lift-off mask M2 having an opening aligned with the upper surface of the ridge structure is formed. The lift-off mask M2 is made of a resist, for example. As shown in part (f) of FIG. 5, after forming the electrode lift-off mask M2, a metal film OH for the ohmic electrode is deposited. The metal film OH can be made of, for example, Pd or Ni / Au.

  As shown in FIG. 6A, the lift-off mask is removed to form a metal stripe that covers the upper surface of the ridge structure. As shown in part (b) of FIG. 6, the back surface of the epitaxial substrate E included in the substrate product is polished to produce a substrate product having a desired thickness. After polishing, as shown in part (c) of FIG. 6, the polished back surface is etched to remove the polishing damage layer. As this etching, ICP dry etching can be performed, and etchant of Cl2 gas is used for polishing damage. As shown in FIG. 6D, an n-side electrode CT (for example, Ti / Al / Au) is formed on the back surface of the etched substrate. If necessary, as shown in FIG. 6 (e), the substrate product is heat-treated for electrode annealing. As shown in part (f) of FIG. 6, a pad electrode AN (for example, Ti / Au) that contacts the metal stripe is formed.

  A semiconductor ridge is formed by etching the Group III nitride semiconductor region. The semiconductor ridge is processed by dry etching. A plurality of semiconductor lasers having different semiconductor ridge heights are manufactured by changing the etching amount by dry etching. In the processing of the semiconductor ridge, the distance from the interface between the active layer and the light guide layer to the bottom of the semiconductor ridge is referred to as a value “D”.

After forming the electrode, the substrate product is cleaved to form an end face for the optical resonator (an end face different from the cleaved face). A dielectric multilayer film is formed on these end faces. The dielectric multilayer film is made of SiO ₂ / TiO ₂ . 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.

Using the same or similar manufacturing conditions as in this example, the laser structure shown in FIGS. 7A, 7B, and 7C is examined. The structure of the epitaxial substrate includes the following.
n-type cladding layer: n-type InAlGaN, In composition 0.02 to 0.04, Al composition 0.09 to 0.21, and film thickness 1000 to 1500 nm.
n-type light guide layer: n-type GaN, film thickness of 150 to 350 nm.
n-side light guide layer: n-type / undoped InGaN, film thickness changed.
p-side light guide layer: undoped InGaN, In composition 0.015 to 0.035, film thickness 0 to 100 nm.
p-type light guide layer: p-type InGaN, In composition 0.015 to 0.035, film thickness 0 to 100 nm.
p-type light guide layer: p-type GaN, film thickness of 150 to 350 nm.
p-type cladding layer: p-type AlGaN, Al composition 0.03-0.06, film thickness 200-600 nm.
p-type contact layer: p + -type GaN, film thickness 10 to 100 nm.
Ridge structure width (TOP): 1.0 μm to 2.5 μm.
Material of the insulating film (protective film): SiO _2, thickness 150 to 500 nm.

When an n-type dopant is added to the n-side InGaN light guide layer, the concentration of the n-type dopant (for example, Si) can be in the range of 3 × 10 ^{17 to} 3 × 10 ¹⁸ cm ⁻³ . The concentration of the p-type dopant (for example, Mg) in the p-type InGaN light guide layer may be in the range of 1 × 10 ¹⁸ to 1 × 10 ¹⁹ cm ⁻³ .

  When an n-type InGaN light guide layer is used, its In composition is preferably in the range of 0.02 to 0.06. When an undoped InGaN light guide layer is provided in the n-side semiconductor region, the In composition is preferably in the range of 0.015 to 0.035. When a p-type InGaN optical guide layer is used, its In composition is preferably in the range of 0.015 to 0.035.

  In this experiment, the width of the ridge structure is 2 μm, and the digging amount D of the ridge structure is 100 nm, for example. FIG. 8 is a drawing showing the FFP divergence angle and the threshold current density in one of the above structures (part (a) of FIG. 7). Referring to FIG. 8A, the relationship between the In composition and the FFP divergence angle in the InGaN optical guide layer is shown. In this graph, “FFP_H” indicates the spread angle in the horizontal direction, and “FFP_V” indicates the spread angle in the vertical direction. Referring to FIG. 8B, the relationship between the thickness of the InGaN optical guide layer and the FFP divergence angle is shown. In this graph, “FFP_H” indicates the spread angle in the horizontal direction, and “FFP_V” indicates the spread angle in the vertical direction. For the n-side InGaN layer, the FFP divergence angle depends more on the film thickness than on the In composition.

List of part (a) of FIG.
In composition, FFP_H (degree), FFP_V (degree).
2.5, 13.66, 23.8.
4.5, 13.52, 24.9.
5.5, 13.44, 25.6.
6.5, 13.36, 26.2.

FIG. 9B is a list of part (b).
Layer thickness, FFP_H (degrees), FFP_V (degrees).
144, 13.66, 23.8.
201, 13.29, 23.7.
259, 12.88, 23.5.
288, 12.66, 23.4.
360, 12.12, 23.0.
450, 11.39, 22.4.
600, 10.12, 21.4.

  Referring to FIG. 8C, the relationship between the thickness of the InGaN optical guide layer and the threshold current density is shown. As the InGaN film thickness increases, the threshold current first decreases. By increasing the thickness of the n-side InGaN light guide layer, when the thickness of the n-side light guide layer relative to the p-side light guide layer is relatively large, the light propagating through the laser waveguide is The ratio absorbed by the p-type dopant in the p-type cladding layer can be lowered. This helps to lower the threshold current as a result. On the other hand, the n-type dopant hardly absorbs light propagating through the laser waveguide. Therefore, the reduction of the threshold current in this range is preferable in the characteristics of the semiconductor laser.

The list of part (c) of FIG.
Layer thickness, threshold current density (A / cm ² ).
144, 5.00.
201, 4.66.
259, 4.47.
288, 4.40.
360, 4.33.
450, 4.36.
600, 4.61.

  The n-type dopant concentration of the n-type InGaN layer in the n-side semiconductor region is lower than the p-type dopant concentration of the p-type InGaN layer in the p-side semiconductor region. Therefore, the amount of light absorption due to the n-type InGaN layer is low. Increasing the film thickness of the n-side InGaN light guide layer increases the proportion of light present in the n-side InGaN guide layer that exhibits a small light absorption, so that the light absorption of the entire waveguide decreases and the threshold is reduced. The value current decreases. However, when the film thickness of the n-side InGaN optical guide layer is further increased, the threshold current increases.

  FIG. 9 shows the results of a simulation conducted as a preliminary experiment. The (a) part, (b) part, and (c) part of FIG. 9 show the spread of propagating light in the n-side InGaN layer (In composition 0.045) having a thickness of 144 nm, 216 nm, and 288 nm, respectively. As the InGaN layer becomes thicker, the spread of light into the ridge structure decreases. This makes it possible to reduce the amount of light absorbed by the p-type semiconductor region. The light amplitude in the well layer is also changed.

  On the other hand, after the threshold current takes the minimum value in the graph of FIG. 8C, the threshold current increases as the InGaN film thickness increases. In the state where most of the propagating light in the laser waveguide is guided away from the active layer, the ratio of the light existing in the well layer is reduced, so that optical amplification is less likely to occur and the threshold current is increased. .

  When based on the criterion that the horizontal FFP divergence angle is, for example, 12 degrees or less, the thickness of the n-side InGaN layer is preferably 370 nm or more from several experiments by the inventors. A thick InGaN layer can cause lattice relaxation. In order to avoid this, the thickness of the n-side InGaN layer is preferably 550 nm or less.

  In addition to the FFP divergence angle, the InGaN layer has a thickness range in which the threshold current density is suitable, which is 100 nm or more and preferably 800 nm or less.

  FIG. 10 is a drawing showing a main process flow 100 in the method of manufacturing the nitride semiconductor light emitting device according to this embodiment. The process flow 100 includes an epitaxial substrate manufacturing process 200 and an electrode and ridge structure manufacturing process 300. In the following description, reference numerals attached to the semiconductor laser shown in FIG. 1 are used for easy understanding. For crystal growth, for example, metal organic vapor phase epitaxy can be used. The epitaxial substrate manufacturing process 200 includes the following processes. In step S100, a group III nitride semiconductor wafer having a semipolar main surface is prepared. In step S101, a first group III nitride semiconductor region 13 is grown on the main surface of the wafer. For example, in step S102, the first cladding layer 23 is grown. The first cladding layer 23 is made of a hexagonal group III nitride semiconductor and has a semipolar surface 13a. In step S <b> 103, the light guide layer 21 is grown on the semipolar surface 23 a of the first cladding layer 23. In step S <b> 104, the light guide layer 21 b is grown on the semipolar surface 23 a of the first cladding layer 23. In step S105, the light guide layer 21a is grown on the semipolar surface of the light guide layer 21b. The light guide layer 21a includes a gallium nitride semiconductor containing indium as a group III constituent element. The thickness of the first light guide layer 21a is 370 nm or more. The material of the light guide layer 21a is different from the material of the light guide layer 21b.

  Next, in step S106, after the growth of the first light guide layer 21a, the gallium nitride based active layer 15 is formed. The oscillation wavelength of the active layer 15 is not less than 400 nm and not more than 550 nm.

  Next, in step S107, after the active layer 15 is grown, the second group III nitride semiconductor region 17 is formed. The second group III nitride semiconductor region 17 includes a light guide layer 25 a, a second cladding layer 27 made of a second conductivity type group III nitride semiconductor, and a p-type contact layer 29. In step S108, the light guide layer 25 (for example, the light guide layer 25a) is grown on the semipolar surface of the active layer 15. The light guide layer 25a is thinner than the light guide layer 21a. The light guide layer 25 includes a light guide layer 25a and a light guide layer 25b. In step S109, the light guide layer 25b is grown on the light guide layer 25a. In step S <b> 110, the second cladding layer 27 is grown on the light guide layer 25. In step S <b> 111, the contact layer 29 is grown on the semipolar surface of the second cladding layer 27. By these steps, an epitaxial substrate is produced.

  In the electrode and ridge structure manufacturing step 300, a substrate line product is manufactured so that the second group III nitride semiconductor region 17 has a ridge structure and an electrode on the ridge structure.

  According to this manufacturing method, it is possible to manufacture a group III nitride semiconductor laser device having a structure capable of bringing the characteristics of the semiconductor laser device close to desired current confinement properties and desired light confinement properties. These steps can be performed according to the steps shown in FIGS. 4 to 6, for example.

  FIG. 11 is a drawing showing a main process flow 400 in the method of manufacturing the nitride semiconductor light emitting device according to this embodiment.

  First, in step S201, a plurality of substrates having a main surface made of hexagonal group III nitride are prepared. These substrates can be, for example, the GaN wafers already described, and their main surfaces can have {20-21} planes, for example. In step S202, a plurality of trial epitaxial substrates are produced from each of the main surfaces of the prepared substrate. In this production, a first group III nitride semiconductor region having a first cladding layer and a first light guide layer is grown on the main surface of the substrate, and then an active layer made of a gallium nitride based semiconductor is grown. Later, a second group III nitride semiconductor region having a second cladding layer and a second light guide layer is grown. With these growths, semiconductor stacks are formed on the major surfaces of the individual substrates. In these semiconductor stacks, the thickness and / or the In composition of the first light guide layer are different from each other. In step S203, a ridge structure and electrodes are formed on the trial epitaxial substrate to produce a plurality of trial substrate products. The formation of the ridge structure and the electrode is not limited. For example, the steps described in the above embodiments can be applied. In step S204, a far-field image of a plurality of trial substrate products is evaluated to obtain a relationship between the far-field image and the thickness (and / or In composition) of the first light guide layer. In addition, or independently, the threshold current for laser oscillation of the trial substrate product is evaluated to determine the threshold current and the thickness of the first light guide layer (and / or (In composition) can be obtained. In step S205, the evaluation result is used to determine the thickness of the first light guide layer for the gallium nitride based semiconductor laser device. In this step, the thickness of the first light guide layer can be determined using the far field image evaluation result and the threshold current evaluation result. In step S206, an epitaxial substrate and a substrate product for the gallium nitride based semiconductor laser device are prepared so that the first light guide layer has the determined thickness. The production of the epitaxial substrate and the substrate product is not limited, but for example, the steps described in the above embodiments can be applied.

  According to this method of manufacturing a gallium nitride based semiconductor laser device, a group III nitride semiconductor laser device having a structure that makes it possible to bring the characteristics of the semiconductor laser device close to a desired optical confinement property can be provided. Further, according to the method of manufacturing the gallium nitride based semiconductor laser device, a group III nitride semiconductor laser having a structure that makes it possible to bring the characteristics of the semiconductor laser device close to desired current confinement properties and desired optical confinement properties An element can be provided.

  In the preparation of the substrate, the normal of the main surface of the substrate is inclined with respect to the c-axis of the group III nitride of the substrate, and the inclination angle of this inclination can be in the range of 10 degrees to 80 degrees. .

  In the formation of the ridge structure, a ridge structure deep enough to locate the bottom of the ridge structure in the second light guide layer in the second group III nitride semiconductor region may be employed. Furthermore, the distance between the bottom of the ridge structure and the active layer is preferably 150 nm or less. According to this manufacturing method, when the distance between the bottom of the ridge structure and the active layer is 150 nm or less, the width of the ridge structure contributes not only to current confinement but also to light confinement.

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

  As described above, according to the present embodiment, a group III nitride semiconductor laser device having a structure that makes it possible to bring the characteristics of the semiconductor laser device close to desired current confinement properties and desired optical confinement properties is provided. Is done. In addition, according to the present embodiment, a method for manufacturing this group III nitride semiconductor laser device is 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 ... Electrode, 21 ... Light guide layer, 23 ... N-type clad Layer, 25 ... light guide layer, 27 ... p-type cladding layer, 29 ... p-type contact layer, Ax ... lamination axis, 31 ... core region, HJ1, HJ2, HJ3 ... heterojunction, 33a ... well layer, 33b ... barrier layer 35 ... Semiconductor ridge, BOTTOM ... Bottom of semiconductor ridge, 37a, 37b ... End face, 39 ... Substrate, 39a ... Semipolar main surface, Angle ... Inclination angle, Sc ... Reference plane.

Claims (21)

A group III nitride semiconductor laser device comprising:
A first group III nitride semiconductor region made of a hexagonal group III nitride semiconductor and having a semipolar plane;
An active layer provided on the semipolar surface of the first group III nitride semiconductor region;
A second group III nitride semiconductor region provided on the semipolar surface of the first group III nitride semiconductor region;
With
The active layer is provided between the first group III nitride semiconductor region and the second group III nitride semiconductor region,
The oscillation wavelength of the active layer is in the range from 510 nm to 540 nm ,
The normal line of the semipolar plane of the first group III nitride semiconductor region is inclined with respect to the c-axis of the group III nitride semiconductor of the first group III nitride semiconductor region,
The inclination angle of the inclination is in the range of 10 degrees to 80 degrees,
The first group III nitride semiconductor region includes a first cladding layer made of a first conductivity type group III nitride semiconductor and a first light guide layer,
The first light guide layer includes a gallium nitride based semiconductor containing indium as a group III constituent element,
The second group III nitride semiconductor region includes a second cladding layer made of a second conductivity type group III nitride semiconductor and a second light guide layer,
The thickness of the second light guide layer is smaller than the thickness of the first light guide layer,
The first light guide layer has a thickness of 370 nm or more;
The second light guide layer has a thickness of 200 nm or less;
The second group III nitride semiconductor region has a ridge structure ;
The bottom of the ridge structure is located in the second light guide layer in the second group III nitride semiconductor region,
The distance between the bottom of the ridge structure and the active layer is 150 nm or less.
Group III nitride semiconductor laser device.   2. The group III nitride semiconductor laser device according to claim 1, wherein the film thickness of the first light guide layer is 550 nm or less. 3. The group III nitride semiconductor laser device according to claim 1, wherein a film thickness of the second light guide layer is 115 nm or less. The ridge structure has an mn plane defined by a normal line of the semipolar plane of the first group III nitride semiconductor region and an m axis of the group III nitride semiconductor of the first group III nitride semiconductor region. The group III nitride semiconductor laser device according to claim 1 , which extends along the line. The first light guide layer is made of ternary InGaN,
The group III nitride semiconductor laser device according to claim 1 , wherein the active layer includes a ternary InGaN layer. The active layer includes an InGaN well layer,
The indium composition of the first light guide layer is smaller than the indium composition of the InGaN well layer,
The group III nitride semiconductor laser device according to claim 1 , wherein an indium composition of the first light guide layer is 2% or more. The active layer includes an InGaN well layer,
The group III nitride semiconductor laser device according to any one of claims 1 to 6 , wherein an indium composition of the first light guide layer is 6% or less and is smaller than an indium composition of the InGaN well layer. . The first group III nitride semiconductor region further includes a third light guide layer,
The third light guide layer comprises a material different from InGaN,
The third light guide layer is provided between the first light guide layer and the first cladding layer;
8. The group III nitride semiconductor laser device according to claim 1 , wherein a thickness of the first light guide layer is larger than a thickness of the third light guide layer. 9. Further comprising an ohmic electrode provided on the upper surface of the ridge structure;
The second group III nitride semiconductor region further includes a contact layer made of a second conductivity type group III nitride semiconductor,
The second cladding layer is provided between the contact layer and the second light guide layer,
The group III nitride semiconductor laser device according to any one of claims 1 to 8 , wherein the ohmic electrode is in contact with the contact layer. The group III nitride semiconductor laser device according to claim 9 , wherein the ohmic electrode comprises palladium. A protective film having an opening matched with the upper surface of the ridge structure and covering the surface of the first group III nitride semiconductor region;
A pad electrode that covers the upper surface of the ohmic electrode and is provided on the protective film;
Further comprising
The protective film covers a side surface of the ridge structure;
The protective film has a refractive index smaller than that of the second group III nitride semiconductor region,
The group III nitride semiconductor laser device according to claim 10 , wherein the ohmic electrode is in contact with the second group III nitride semiconductor region through the opening of the protective film. Further comprising a substrate having a semipolar main surface made of hexagonal group III nitride,
Wherein the 1III nitride semiconductor region, the active layer and the first 2III nitride semiconductor region, the said substrate being placed in the direction normal to the semipolar primary surface, any one of claims 1 to 11 A group III nitride semiconductor laser device according to item 1. The normal line of the semipolar main surface of the substrate is inclined with respect to the c-axis of the group III nitride of the substrate,
The group III nitride semiconductor laser device according to claim 12 , wherein an inclination angle of the inclination is in a range of not less than 63 degrees and not more than 80 degrees. 14. The group III nitride semiconductor laser device according to claim 13 , wherein the substrate includes a hexagonal conductive group III nitride that is any one of GaN, InGaN, AlGaN, and InAlGaN. Said first cladding layer is of n conductivity _{In X1 Al Y1 Ga 1-X1} -Y1 N (0 <X1 <0.05,0 <Y1 <0.20), according to claim 1 to claim 14 A group III nitride semiconductor laser device according to any one of the above. Said second cladding layer is of p conductivity _{In X2 Al Y2 Ga 1-X2} -Y2 N (0 <X2 <0.05,0 <Y2 <0.20), according to claim 1 to claim 15 A group III nitride semiconductor laser device according to any one of the above. A method for producing a group III nitride semiconductor laser device, comprising:
Growing a first cladding layer made of a hexagonal group III nitride semiconductor and having a semipolar plane;
Growing a first light guide layer on the semipolar surface of the first cladding layer;
Forming a gallium nitride based active layer after the growth of the first light guide layer;
Forming a group III nitride semiconductor region having a ridge structure after the growth of the active layer; and
With
The oscillation wavelength of the active layer is 510 nm or more and 540 nm or less ,
The normal line of the semipolar plane of the first cladding layer is inclined with respect to the c-axis of the group III nitride semiconductor of the first cladding layer,
The inclination angle of the inclination is in the range of 10 degrees to 80 degrees,
The first light guide layer includes a gallium nitride based semiconductor containing indium as a group III constituent element,
The group III nitride semiconductor region includes a second cladding layer and a second light guide layer,
The thickness of the second light guide layer is smaller than the thickness of the first light guide layer,
The first light guide layer has a thickness of 370 nm or more ;
The second light guide layer has a thickness of 200 nm or less;
The bottom of the ridge structure is located in the second light guide layer in the group III nitride semiconductor region,
A method for producing a group III nitride semiconductor laser device, wherein a distance between the bottom of the ridge structure and the active layer is 150 nm or less . The method for producing a group III nitride semiconductor laser device according to claim 17 , wherein the film thickness of the first light guide layer is 550 nm or less. The method for producing a group III nitride semiconductor laser device according to claim 17 or 18, wherein the thickness of the second light guide layer is 115 nm or less. A method of manufacturing a gallium nitride based semiconductor laser device,
Preparing a plurality of substrates having a principal surface composed of a hexagonal group III-nitride;
A first group III nitride semiconductor region having a first cladding layer and a first light guide layer, an active layer made of a gallium nitride based semiconductor, and a second group III nitride semiconductor region having a second cladding layer and a second light guide layer A plurality of trial epitaxial substrates having different thicknesses of the first light guide layers;
Forming a plurality of trial substrate products by forming ridge structures and electrodes on the plurality of trial epitaxial substrates;
Performing a far-field image evaluation of the plurality of trial substrate products to obtain a relationship between the far-field image and the thickness of the first light guide layer;
Determining the thickness of the first light guide layer for the gallium nitride based semiconductor laser device using the result of the evaluation;
Producing an epitaxial substrate for the gallium nitride based semiconductor laser device so that the first light guide layer has the determined thickness,
The oscillation wavelength of the active layer is 510 nm or more and 540 nm or less,
The normal of the main surface of the substrate is inclined with respect to the c-axis of the group III nitride of the substrate,
The inclination angle of the inclination is in the range of 10 degrees to 80 degrees,
The first light guide layer includes a gallium nitride based semiconductor containing indium as a group III constituent element,
The thickness of the second light guide layer is smaller than the thickness of the first light guide layer,
The bottom of the ridge structure is located in the second light guide layer in the second group III nitride semiconductor region,
A method for producing a group III nitride semiconductor laser device, wherein a distance between the bottom of the ridge structure and the active layer is 150 nm or less . Further comprising evaluating a threshold current for laser oscillation of the plurality of trial substrate products to obtain a relationship between the threshold current and the thickness of the first light guide layer;
In the step of determining the thickness of the first light guide layer, the thickness of the first light guide layer is determined using the evaluation result of the far-field image and the evaluation result of the threshold current. A method for producing a group III nitride semiconductor laser device according to claim 20 .

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