JP2019204847A - Nitride semiconductor laser element - Google Patents

Abstract

To provide a nitride semiconductor laser element which enables the achievement of a high output.SOLUTION: A nitride semiconductor laser element 1 comprises a nitride semiconductor laminate film 12 which includes a lower guide layer 122a formed by AlGaN, a luminescent layer 121 having a well layer 121a formed by AlGaN, an upper guide layer 122b formed by AlGaN, and a composition-changing layer 123 of which the Al composition ratio of AlGaN continuously or stepwisely decreases further at greater distances from the upper guide layer 122b. Supposing that a minimum value of x3 of AlGaN is y, a maximum value is z, a film thickness of the lower guide layer 122a is T1, a film thickness of the luminescent layer 121 is T2, and a film thickness of the upper guide layer 122b is T3, the nitride semiconductor laminate film 12 has a composition that satisfies a relation given by x2<x1<y and -1<x1-y<0.2, and it has a film thickness that satisfies a relation given by 40 nm<T1+T2+T3<600 nm.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a nitride semiconductor laser device.

  Patent Document 1 discloses a nitride semiconductor laser element. In Patent Document 1, the threshold current is reduced by making the refractive index of the active layer side region in the p-type cladding layer lower than the refractive index of the region opposite to the active layer side in the p-type cladding layer. In addition, it is described that the slope efficiency is improved and the output power of the nitride semiconductor laser element can be increased. Increasing the output of the nitride-based semiconductor laser device is an infinite demand.

JP 2011-210951 A

  An object of the present invention is to provide a nitride semiconductor laser device capable of achieving high output.

In order to achieve the above object, a nitride semiconductor laser device according to an aspect of the present invention includes a lower guide layer formed of Al _x1 Ga _(1-x1) N, and is stacked on the lower guide layer to form Al _x2. A light emitting layer having a well layer formed of Ga _(1-x2) N, an upper guide layer stacked on the light emitting layer and formed of Al _x1 Ga _(1-x1) N, and the upper guide layer _{Al x3 Ga (1-x3)} the higher is formed by laminating the N away from the upper guide layer _{Al x3 Ga (1-x3)} composition change layer Al composition decreases continuously or stepwise in N above A nitride semiconductor multilayer film, a p-type electrode and an n-type electrode for injecting current into the nitride semiconductor multilayer film, wherein x is the minimum value of x 3 of Al _x3 Ga _(1-x3) N, and y is the maximum value. Z and the lower guide layer When the film thickness is T1, the light emitting layer is T2, and the upper guide layer is T3, the nitride semiconductor multilayer film has 0 ≦ x1 ≦ 1, 0 ≦ x2 ≦ 1, 0 ≦. It has a composition satisfying the relationship of x3 ≦ 1, x2 <x1 <z and −1 <x1-y <0.2, and has a film thickness satisfying the relationship of 40 nm <T1 + T2 + T3 <600 nm.

  In order to achieve the above object, a nitride semiconductor laser device according to another aspect of the present invention includes a lower guide layer, a light emitting layer stacked on the lower guide layer and having a well layer, and an upper surface of the light emitting layer. A nitride semiconductor multilayer film having an upper guide layer laminated on the upper guide layer and a composition change layer laminated on the upper guide layer and having a composition changed continuously or stepwise in a film thickness direction, and the nitride semiconductor multilayer A p-type electrode and an n-type electrode for injecting a current into the film; the refractive index of the lower guide layer is n1, the band gap is E1, the film thickness is T1, the refractive index of the well layer is n2, and the band gap is E2, the thickness of the light emitting layer is T2, the refractive index of the upper guide layer is n3, the band gap is E3, the film thickness is T3, and the range in which the refractive index and band gap of the composition change layer changes is n4. To n5 and 4 to E5, and the film thickness of the composition change layer is Tc, the nitride semiconductor multilayer film has a composition satisfying the relationship of n4 <n1, −0.5 <E5-E1 <1.3, and 40 nm < The composition change layer has a film thickness satisfying a relationship of T1 + T2 + T3 <600 nm, and the refractive index increases continuously or stepwise as the distance from the upper guide layer increases.

  According to each aspect of the present invention, high output can be achieved.

1 is a perspective view showing a schematic configuration of a nitride semiconductor laser element 1 according to first and second embodiments of the present invention. FIG. 1 is a side view of a main part showing a schematic configuration of a nitride semiconductor laser device 1 according to a first embodiment and a second embodiment of the present invention. FIG. 2 is a diagram for explaining a nitride semiconductor laser device 1 according to a first embodiment of the present invention, and is a total thickness (T1 + T2 + T3) of respective thicknesses of a light emitting layer 121 and a guide layer 122 provided in the nitride semiconductor laser device 1; ) And the optical confinement coefficient Γ of the guide layer 122. FIG. FIG. 6 is a diagram for explaining a nitride semiconductor laser device 1 according to the first embodiment of the present invention, in which the difference between the Al composition ratio x1 of the upper guide layer 122b and the maximum value z of the Al composition ratio of the composition change layer 123 is determined; 6 is a graph showing a simulation result of a relationship with an optical confinement coefficient Γ of a layer 122. 1 is a diagram for explaining a nitride semiconductor laser device 1 according to a first embodiment of the present invention, in which a total thickness T1 + T2 + T3 of a guide layer 122 and a light emitting layer 121 provided in the nitride semiconductor laser device 1 and a nitride semiconductor laser device are provided. It is a graph which shows the simulation result of the relationship with the threshold current density Jth of 1. 1 is a diagram for explaining a nitride semiconductor laser device 1 according to a first embodiment of the present invention, from a region 123d of a composition change layer 123 provided in the nitride semiconductor laser device 1 to an uppermost end of the nitride semiconductor multilayer film 12. FIG. 6 is a graph showing a simulation result of the relationship between the ratio of the total film thickness of the guide layer 122 and the light emitting layer 121 to the distance T4 and the light confinement coefficient Γ of the guide layer 122. FIG. 2 is a diagram for explaining a nitride semiconductor laser device 1 according to a first embodiment of the present invention, in which the difference y− between the Al composition ratio x4 of the lower cladding layer 13 and the minimum value y of the Al composition ratio x3 of the composition change layer 123 is illustrated. 7 is a graph showing a simulation result of a relationship between x4 and a light confinement coefficient Γ of a guide layer 122. 1 is a diagram for explaining a nitride semiconductor laser device 1 according to a first embodiment of the present invention, from a region 123d of a composition change layer 123 provided in the nitride semiconductor laser device 1 to an uppermost end of the nitride semiconductor multilayer film 12. FIG. 6 is a graph showing a simulation result of the relationship between the ratio of the total film thickness of the guide layer 122 and the light emitting layer 121 to the distance T4 and the threshold current density Jth of the nitride semiconductor laser device 1. 1 is a diagram for explaining a nitride semiconductor laser device 1 according to a first embodiment of the present invention, in which a film thickness T5 of a nitride semiconductor layer 14 provided in the nitride semiconductor laser device 1 and a threshold value of the nitride semiconductor laser device 1 are illustrated. It is a graph which shows the simulation result of the relationship with current density Jth.

[First Embodiment]
The nitride semiconductor laser device according to the first embodiment of the present invention will be described with reference to FIGS. First, the schematic configuration of the nitride semiconductor laser element 1 according to the present embodiment will be described with reference to FIG. In FIG. 1, a nitride semiconductor laser device 1 is schematically illustrated. In FIG. 1, for easy understanding, the relative relationships between the thicknesses and sizes of the layers constituting the nitride semiconductor laser element 1 are shown different from the actual dimensions.

  As shown in FIG. 1, the nitride semiconductor laser device 1 includes a substrate 11, a nitride semiconductor multilayer film 12 disposed above the substrate 11, and a p-type electrode 15 that injects current into the nitride semiconductor multilayer film 12. And an n-type electrode 16. The nitride semiconductor multilayer film 12 includes a lower guide layer 122a, a light emitting layer 121 stacked on the lower guide layer 122a and having a well layer 121a, an upper guide layer 122b stacked on the light emitting layer 121, and an upper portion And a composition change layer 123 laminated on the guide layer 122b.

  The nitride semiconductor laser device 1 includes a lower cladding layer 13 formed below the lower guide layer 122a and a nitride semiconductor layer 14 formed above the composition change layer 123. The composition change layer 123 and the nitride semiconductor layer 14 constitute an upper cladding layer. The p-type electrode 15 is formed on the nitride semiconductor layer 14, and the n-type electrode 16 is formed on the lower cladding layer 13. Although illustration is omitted, a laser diode packaged by the nitride semiconductor laser element 1 and a package covering the nitride semiconductor laser element 1 is configured. This package mainly has a support body made of gold or lead as a base, and has a window made of glass in a region where light emitted from the light emitting layer 121 is incident. The light emitting layer 121 can emit ultraviolet light having a wavelength of 360 nm or less.

  The lower guide layer 122a, the light emitting layer 121, the upper guide layer 122b, and the composition change layer 123 are stacked above the substrate 11 in this order. The lower guide layer 122a and the upper guide layer 122b constitute a guide layer 122. The lower cladding layer 13, the nitride semiconductor multilayer film 12, and the nitride semiconductor layer 14 constitute a nitride multilayer body 10.

  The substrate 11 has a thin quadrangular shape. The substrate 11 has a laminated surface 11S on which the lower cladding layer 13, the nitride semiconductor laminated film 12, and the nitride semiconductor layer 14 are laminated. The stacked surface 11 </ b> S is a flat surface in contact with the nitride stacked body 10. The nitride laminate 10 is formed on the substrate 11 so that the side wall is substantially orthogonal to the laminate surface 11S. Note that the side wall of the substrate 11 and the side wall of the nitride laminate 10 may be formed flush with each other. The lower cladding layer 13 of the nitride laminate 10 is formed in contact with the laminate surface 11S. The substrate 11 may have a single substrate structure, or may have a stacked structure in which semiconductors are stacked on the substrate. Examples of the laminated structure of the substrate 11 include a structure in which an AlN thin film is laminated on a sapphire substrate, and a structure in which an AlN thin film and an n-type AlGaN thin film are laminated on a sapphire substrate.

The lower guide layer 122a is made of, for example, Al _x1 Ga _(1-x1) N. X1 that determines the composition of the lower guide layer 122a may be any value in the range of 0 to 1 (0 ≦ x1 ≦ 1).

The upper guide layer 122b is made of, for example, Al _x1 Ga _(1-x1) N. X1 that determines the composition of the upper guide layer 122b may be any value in the range of 0 or more and 1 or less (0 ≦ x1 or less 1). The upper guide layer 122b and the lower guide layer 122a may have the same or different Al composition (that is, the value of x1), but are preferably the same in order to efficiently confine light.

The well layer 121a provided in the light emitting layer 121 is made of, for example, Al _x2 Ga _(1-x2) N. In the present embodiment, the light emitting layer 121 has a barrier layer made of, for example, AlGaN, and has a multiple quantum well (MQW) structure in which the well layers 121a and the barrier layers are alternately stacked one by one. In the nitride semiconductor laser device 1, the light emitting layer 121 has a multiple quantum well structure, so that the light emission efficiency and light emission intensity of the light emitting layer 121 are improved.

  The light emitting layer 121 may have, for example, a double quantum well structure of “barrier layer / well layer / barrier layer / well layer / barrier layer”. The thickness of each of these well layers may be 3 nm, for example, the thickness of each of these barrier layers may be 10 nm, for example, and the thickness of the light emitting layer 121 may be 36 nm. Hereinafter, the two well layers included in the light emitting layer 121 are collectively referred to as a “well layer 121a”. Therefore, the thickness T2 of the light emitting layer 121 indicates the total thickness of the plurality of well layers 121a and the plurality of barrier layers. X2 that determines the composition of the well layer 121a may be any value in the range of 0 to 1 (0 ≦ x2 ≦ 1).

  The guide layer 122 has an emission side end face 122Sa on the side from which the light emitted from the light emitting layer 121 is emitted. The exit end face 122Sa of the guide layer 122 constitutes a half mirror, and the opposing end face 122Sb of the guide layer 122 facing the exit side end face 122Sa constitutes a mirror. The guide layer 122 confines the light emitted from the light emitting layer 121 due to a difference in refractive index between the lower cladding layer 13 and the upper cladding layer 123.

  The guide layer 122 uses the refractive index difference between the air that fills the external space of the nitride semiconductor laser element 1 and the guide layer 122 to form a half mirror at the exit-side end surface 122Sa and a mirror at the opposing end surface 122Sb. May be. Further, the guide layer 122 has a dielectric multilayer film formed on each surface of the emission side end surface 122Sa and the opposite end surface 122Sb in order to improve the reflectance at the emission side end surface 122Sa and the opposite end surface 122Sb. A half mirror may be configured, and the mirror may be configured with the opposed end surface 122Sb.

  The composition change layer 123 has a ridge structure. That is, the composition change layer 123 has a shape in which a part of the surface (upper surface) that is not in contact with the upper guide layer 122b protrudes upward in a bank shape. The composition change layer 123 has this projecting portion at substantially the center, but it may have a projecting portion that is offset toward the side where the n-type electrode 16 is disposed instead of the center. Since the projecting portion approaches the n-type electrode 16, the current path flowing in the nitride laminate 10 is shortened, so that the resistance value of the current path formed in the nitride laminate 10 can be lowered. A nitride semiconductor layer may be provided between the light emitting layer 122 and the composition gradient layer 123. For example, a barrier layer called an “electron blocking layer” may be provided to improve luminous efficiency. Further, the bottom of the ridge structure is not necessarily formed by a composition gradient layer, and may be, for example, the electron block layer or a nitride semiconductor layer on the composition gradient layer. Further, the ridge structure may not be provided.

The composition change layer 123 is configured such that the Al composition of Al _x3 Ga _(1-x3) N decreases continuously or stepwise as the distance from the upper guide layer 122 b increases. X3 that determines the composition of the composition change layer 123 may vary in the range of 0 to 1 (0 ≦ x3 ≦ 1). Therefore, the composition change layer 123 has a structure in which x3 changes within a range greater than 0 and less than 1 and is formed of only Al _x3 Ga _(1-x3) N, and changes in a range where x3 is greater than 0 and less than or equal to 1. A structure formed of AlN and Al _x3 Ga _(1-x3) N, a structure formed of Al _x3 Ga _(1-x3) N and GaN by changing _x3 in a range of 0 or more and less than 1, and x3 It changes in the range of 0 or more and 1 or less, and has one of the structures formed of AlN, Al _x3 Ga _(1-x3) N and GaN.

The Al composition change rate in the composition change layer 123 is greater than 0.1% / nm. Here, the Al composition change rate refers to the rate at which the Al composition ratio, which is the number of moles of Al, with respect to the total number of moles of Al and Ga in AlGaN changes. By defining the composition change rate within this range, the amount of holes generated by polarization doping described later can be increased. Thereby, holes can be efficiently transported to the light emitting layer 121, and a nitride semiconductor laser element 1 having high luminous efficiency and a laser diode including the nitride semiconductor laser element 1 can be manufactured. When the minimum value of x3 of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is y and the maximum value is z, the lower region 123a of the composition change layer 123 on the guide layer 122 side is Al _z Ga _{(1 -Z)} The upper region 123b of the composition change layer 123 on the nitride semiconductor layer 14 side is formed of Al _y Ga _(1-y) N. In the intermediate region 123c between the lower region 123a and the upper region 123b of the composition change layer 123, the Al composition ratio of Al _x3 Ga _(1-x3) N, that is, the value of x3 is continuous from the lower region 123a toward the upper region 123b. Alternatively, it may be formed of Al _x3 Ga _(1-x3) N that decreases in a stepwise or stepwise manner. Further, the intermediate region 123c is _one composition ratio between the Al composition ratio of Al _x3 Ga _(1-x3) N in the lower region 123a and the Al composition ratio of Al _x3 Ga _(1-x3) N in the upper region 123b. , i.e. _{Al x3 Ga (1-x3)} x3 of N may be formed by _{Al x3 Ga (1-x3)} N single value between y and z. In addition, the composition change layer 123 in the present embodiment has a three-layer structure of the lower region 123a, the upper region 123b, and the intermediate region 123c, but does not have the intermediate region 123c and includes the lower region 123a and the upper region 123b. It may have a two-layer structure. In this case, the composition change layer 123 has a structure in which the composition of Al _x3 Ga _(1-x3) N is changed in two stages.

In this embodiment, the minimum value y of x3 of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is 0.2 or more and 0.8 or less (0.2 ≦ y ≦ 0.8). May be. Further, assuming that the maximum value z of x 3 of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is larger than the value of the minimum value y, it is 0.3 to 1 (0.3 ≦ 1). z ≦ 1). The composition change layer 123 is formed by polarization doping by forming the composition change layer 123 while controlling at least one of the minimum value y and the maximum value z of x 3 of Al _x3 Ga _(1-x3) N to be a value in this range. The hole density in 123 is improved. Furthermore, the composition change layer 123 is formed by forming the composition change layer 123 by controlling at least one of the minimum value y and the maximum value z of x 3 of Al _x3 Ga _(1-x3) N to be a value within this range. This improves the effect of confining the light emitted from the light emitting layer 121 in the guide layer 122 by using the refractive index. Thus, by optimizing the minimum value y and the maximum value z of Al _x3 Ga _(1-x3) N constituting the composition change layer 123, the hole density in the composition change layer 123 due to polarization doping can be reduced. Both improvement and improvement of the light confinement effect of the guide layer 122 can be achieved. Thereby, the nitride semiconductor laser device 1 can achieve high output.

  By including the composition change layer 123, the nitride semiconductor laser element 1 can suppress abrupt composition change in the nitride semiconductor multilayer film 12, and suppress deterioration of flatness of the thin film due to three-dimensional growth.

The nitride semiconductor multilayer film 12 has a composition that satisfies the relationship of the following formulas (1) to (5).
0 ≦ x1 ≦ 1 (1)
0 ≦ x2 ≦ 1 (2)
0 ≦ x3 ≦ 1 (3)
x2 <x1 <z (4)
-1 <x1-y <0.2 (5)

  By satisfying the relationship of the formula (4), carriers injected from the lower cladding layer 13 can be confined without escaping to the nitride semiconductor layer 14 side. Further, by satisfying the relationship of the formula (5), the light emitted from the light emitting layer 121 can be confined in the guide layer 122 without passing to the nitride semiconductor layer 14 side (details will be described later).

In the case where the well layer 121a is formed of Al _x2 Ga _(1-x2) N, the well layer 121a and the composition change layer 123 have a composition that satisfies the relationship of the following formula (6).
x2 <y (6)
By satisfying the relationship of Expression (6), there is no region having a band gap smaller than that of the light emitting layer 121 in the composition changing layer 123, and light emission from the light emitting layer 121 can be suppressed from being absorbed by the composition changing layer 123 (details). Will be described later).

  Regarding the relationship between the Al composition in AlGaN and the refractive index in the wavelength region of ultraviolet light, it is known that the refractive index increases when the Al composition is low, and the refractive index decreases when the Al composition is high. For this reason, the refractive index in the composition change layer 123 in the wavelength region of light emitted from the light emitting layer 121 (that is, the wavelength region of ultraviolet light) is lower in the lower region 123a than in the upper region 123b. Thereby, the composition change layer 123 can reduce the amount of the light confined in the guide layer 122 to the nitride semiconductor layer 14. As a result, the nitride semiconductor laser element 1 can improve the optical confinement efficiency, and can realize a high-power laser element.

The lower guide layer 122a, the upper guide layer 122b, and the well layer 121a may have a composition that satisfies the relationship of the following formula (7).
0.05 ≦ x1-x2 ≦ 0.2 (7)

  Since the lower guide layer 122a, the upper guide layer 122b, and the well layer 121a have a composition satisfying the relationship of the formula (7), carriers injected from the cladding layer into the guide layer can be efficiently confined in the well layer of the light emitting layer. It becomes possible. This makes it possible to manufacture a laser element with high emission efficiency.

The lower guide layer 122a, the upper guide layer 122b, and the composition change layer 123 may have a composition that satisfies the relationship of the following formula (8).
0.05 ≦ z−x1 ≦ 0.3 (8)

  Since the lower guide layer 122a, the upper guide layer 122b, and the composition change layer 123 have a composition satisfying the relationship of the formula (8), the efficiency of confining the light emitted from the light emitting layer 121 by the guide layer 122 and the light emitting layer 121 are improved. It is possible to achieve both improvement in the efficiency of injecting carriers (electrons and holes) into the substrate.

The lower cladding layer 13 includes n-type Al _x4 Ga _(1-x4) N. The lower cladding layer 13 in the present embodiment is entirely formed of n-type Al _x4 Ga _(1-x4) N, that is, an n-type semiconductor. The lower cladding layer 13 and the composition change layer 123 have compositions that satisfy the relationship of the following formula (9).
0 ≦ x4-y <0.4 (9)

  By satisfying the relationship of Expression (9), the difference in refractive index between the upper cladding layer composed of the composition change layer 123 and the nitride semiconductor layer 14 and the lower cladding layer 13 becomes small, and light emission from the light emitting layer 121 occurs. The bias to either the upper cladding layer or the lower cladding layer 13 can be suppressed. Thus, the light leakage into the upper cladding layer and the lower cladding layer 13 can be suppressed, and the light absorption in the upper cladding layer and the lower cladding layer 13 can be suppressed. The light emission output of the element 1 can be improved.

In addition, _x4 that determines the composition of Al _x4 Ga _(1-x4) N constituting the lower cladding layer 13 and the maximum of x3 that determines the composition of Al _x3 Ga _(1-x3) N that constitutes the composition change layer 123. The difference from the value z may be greater than or equal to 0 and less than 0.4. In this case, the value of x4 may be larger than the value of z, and the value of z may be larger than the value of x4. As a result, the difference between the refractive index of the lower cladding layer 13 and the refractive index of the composition change layer 123 becomes smaller than 0.4, so that the bias of light emission from the light emitting layer 121 is suppressed, and the nitride semiconductor laser device 1. The light emission output can be improved.

  The lower cladding layer 13 is formed to be slightly smaller than or the same size as the substrate 11. Thereby, the laminated surface 11S is exposed around the lower cladding layer 13. The lower cladding layer 13 includes a first region 131 where the guide layer 122 is stacked, and a second region 132 whose height from the stacked surface 11S is lower than that of the first region 131. The lower cladding layer 13 has a step at the boundary between the first region 131 and the second region 132. An n-type electrode 16 is formed on the second region 132. The n-type electrode 16 serves as an electrode on the negative electrode side of the current injected into the light emitting layer 121. Electrons are supplied to the lower cladding layer 13 through the n-type electrode 16.

The lower cladding layer 13, the lower guide layer 122a, and the upper guide layer 122b may have a composition that satisfies the relationship of the following formula (10).
0.05 ≦ x4-x1 ≦ 0.3 (10)

  Since the lower cladding layer 13, the lower guide layer 122 a, and the upper guide layer 122 b have a composition that satisfies the relationship of Expression (10), the efficiency of confining the light emitted from the light emitting layer 121 by the guide layer 122 is improved, and the light emitting layer 121 is used. It is possible to achieve both improvement in the efficiency of injecting carriers (electrons and holes) into the substrate.

The nitride semiconductor layer 14 is made of p-type Al _x5 Ga _(1-x5) N. Al _x5 Ga _(1-x5) N constituting the nitride semiconductor layer 14 has a composition satisfying the relationship of the following formula (11).
0 ≦ x5 ≦ y (11)

  The nitride semiconductor layer 14 is formed on the protruding portion of the composition change layer 123. For this reason, the upper cladding layer composed of the composition change layer 123 and the nitride semiconductor layer 14 has a ridge structure. A p-type electrode 15 is formed on the nitride semiconductor layer 14. The nitride semiconductor layer 14 functions as a contact layer with the p-type electrode 15 in the upper cladding layer formed by the composition change layer 123 and the nitride semiconductor layer 14. The p-type electrode 15 becomes an electrode on the positive electrode side of the current injected into the light emitting layer 121. Holes are supplied to the nitride semiconductor layer 14 through the p-type electrode 15.

  When the upper cladding layer has a ridge structure, the threshold current for forming an inversion distribution necessary for laser oscillation can be lowered. Further, since confinement of light in the horizontal direction perpendicular to the resonance direction can be realized, laser oscillation can be controlled to a single mode. As shown in FIG. 1, the ridge structure in the nitride semiconductor laser device 1 has a protruding portion in which a part of the composition change layer 123 protrudes, the nitride semiconductor layer 14 disposed on the protruding portion, and the p-type electrode 15. And may be configured. The ridge structure in the nitride semiconductor laser device 1 includes a bank-like composition change layer 123 formed on a part of the upper guide layer 122b, and a nitride semiconductor layer 14 formed on the composition change layer 123. The p-type electrode 15 may be formed on the nitride semiconductor layer 14. Since the nitride semiconductor laser element 1 has such a ridge structure, the current path in the upper clad layer can be limited to a region directly under the electrode. As a result, current diffusion in the horizontal direction in the upper cladding layer is suppressed, so that the current flowing in the light emitting layer 121 is concentrated directly below the protruding portion of the upper cladding layer (in this embodiment, the protruding portion of the composition change layer 123). Can be made. As a result, an inversion distribution state can be efficiently formed in the region of the protruding portion, and the laser oscillation threshold value can be kept low.

  After the inversion distribution region is formed in the light emitting layer 121, the holes injected into the nitride semiconductor layer 14 and the electrons injected into the lower cladding layer 13 are recombined in the light emitting layer 121. Light is generated. The refractive index of the composition change layer 123 and the lower cladding layer 13 is larger than that of the guide layer 122. Therefore, the light emitted from the light emitting layer 121 is reflected by the surface of the composition change layer 123 and the lower cladding layer 13 that are in contact with the guide layer 122, and is confined in the guide layer 122. Since the emission-side end surface 122Sa and the opposed end surface 122Sb of the guide layer 122 exhibit a function as a mirror (reflecting mirror), the light emitted from the light-emitting layer 121 reciprocates while being amplified in the guide layer 122 to generate stimulated emission. Laser oscillation occurs. When the light amplified in the guide layer 122 becomes larger than the optical loss in the guide layer 122, the light is emitted from the nitride semiconductor multilayer film 12 to the outside.

On the premise that the nitride semiconductor layer 14 satisfies the relationship of the formula (11), the value of x 5 of Al _x5 Ga _(1-x5) N is 0 or more and 0.2 or less (0 ≦ x5 ≦ 0.2). It may be. When the nitride semiconductor layer 14 is formed of Al _x5 Ga _(1-x5) N (where 0 ≦ x5 ≦ 0.2), the contact resistance between the nitride semiconductor layer 14 and the p-type electrode 15 is reduced. . Thereby, the nitride semiconductor laser device 1 can achieve low power consumption. In the present embodiment, the nitride semiconductor layer 14 is made of, for example, GaN (x5 = 0).

  Next, the thickness of each layer constituting the nitride semiconductor laser element 1 will be described with reference to FIGS.

As shown in FIG. 2, when the film thickness of the lower guide layer 122a is T1, the film thickness of the light emitting layer 121 is T2, and the film thickness of the upper guide layer 122b is T3, the nitride semiconductor multilayer film 12 has the following structure: It has a film thickness satisfying the relationship of Expression (12).
40 nm <T1 + T2 + T3 <600 nm (12)

  Since the nitride semiconductor multilayer film 12 has a film thickness in the range shown in Formula (12), the nitride semiconductor laser device 1 can achieve high output.

  Here, the optical confinement coefficient Γ of the guide layer 122 and the threshold current density Jth of the nitride semiconductor laser device 1 will be described with reference to FIGS. 3 to 9 with reference to FIG. FIGS. 3 to 8 show graphs calculated using the simulation software SiLENSe Laser Edition.

The laminated structure of the nitride semiconductor laser element which is a hypothesis of this simulation is the same as that of the nitride semiconductor laser element 1 shown in FIGS. More specifically, the substrate 11 is an AIN substrate having a thickness of 2 μm, and the lower cladding layer 13 has an Al composition of Al _x4 Ga _(1-x4) N of 60% (that is, x4 = 0.6), and an impurity. As a 1 μm n-type semiconductor layer containing 3 × 10 ¹⁸ cm ⁻³ of Si. Further, the lower guide layer 122a and the upper guide layer 122b are layers in which the Al composition of Al _x1 Ga _(1-x1) N is 50% (that is, x1 = 0.5), and the thicknesses thereof are appropriately changed. The light emitting layer 121 has a double quantum well structure of “barrier layer / well layer 121a / barrier layer / well layer 121a / barrier layer”, and the well layer 121a has an Al composition of Al _x2 Ga _(1-x2) N. The barrier layer was a 10 nm thick layer with an Al composition of 50%. The composition of the composition change layer 123 is changed as appropriate, the thickness is set to 150 nm or 300 nm, and Mg is included as an impurity at 3 × 10 ¹⁹ cm ⁻³ . In addition, the nitride semiconductor layer 14 is a layer in which the Al composition of Al _x5 Ga _(1-x5) N is 0% (that is, x5 = 0), that is, a layer formed of GaN, and impurities are 3 × 10 ²⁰ cm ^−3. The thickness was appropriately changed. In each layer, the electron mobility was 100 mc ² · Vs, and the hole mobility was 10 cm ² · Vs. The dislocation density was 1 × 10 ⁹ cm ⁻² . Furthermore, the growth surface was 0001.

  In this simulation, the thickness of the lower cladding layer 13 was set to 1000 nm. The film thicknesses of the lower guide layer 122a and the upper guide layer 122b were appropriately changed. The two well layers 121a are non-doped nitride layers and have a thickness of 3 nm. The three barrier layers were non-doped nitride layers, and the film thickness was 10.0 nm. The film thickness of the composition change layer 123 was 300 nm. The film thickness of the nitride semiconductor layer 14 was 10 nm.

  The horizontal axis of the graph shown in FIG. 3 indicates the total film thickness T1 + T2 + T3 [nm], which is the sum of the thicknesses of the light emitting layer 121 and the guide layer 122, and the vertical axis of the graph indicates the optical confinement coefficient Γ of the guide layer 122. ing. Hereinafter, the “total film thickness of the light emitting layer 121 and the guide layer 122 combined” may be abbreviated as “total film thickness of the light emitting layer 121 and the guide layer 122”, and “T1 + T2 + T3” may be referred to as “ΣT”. May be called. The light confinement coefficient is calculated by a value obtained by dividing the value of the well distribution 121a in the light distribution by the total integrated value of the light distribution.

The shaded square marks in FIG. 3 are obtained when the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is changed from 80% to 0% (that is, y = 0 and z = 0.8) shows the relationship between the film thickness T3 of the upper guide layer 122b and the optical confinement coefficient Γ of the guide layer 122. The hatched rhombus marks shown in FIG. 3 are obtained when the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is changed from 80% to 20% (that is, y = 0.2 and The relationship between the film thickness T3 of the upper guide layer 122b at z = 0.8) and the optical confinement coefficient Γ of the guide layer 122 is shown.

The white diamonds in FIG. 3 indicate the case where the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is changed from 80% to 30% (ie, y = 0.3 and z = 0.8) The relationship between the film thickness T3 of the upper guide layer 122b and the optical confinement coefficient Γ of the guide layer 122 is shown. The white circles in FIG. 3 indicate the case where the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is changed from 80% to 40% (ie, y = 0.4 and z = 0.8) The relationship between the film thickness T3 of the upper guide layer 122b and the optical confinement coefficient Γ of the guide layer 122 is shown. The white triangles shown in FIG. 3 indicate the case where the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is changed from 80% to 50% (ie, y = 0.5 and z = 0.8) The relationship between the film thickness T3 of the upper guide layer 122b and the optical confinement coefficient Γ of the guide layer 122 is shown. 3 indicates the case where the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is changed from 80% to 70% (that is, y = 0.7 and z = 0). 8) shows the relationship between the film thickness T3 of the upper guide layer 122b and the optical confinement coefficient Γ of the guide layer 122. 3 indicates the film thickness T3 of the upper guide layer 122b in the case of a single aluminum layer in which the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is constant at 80%. The relationship with the optical confinement coefficient Γ of the guide layer 122 is shown.

In FIG. 3, the change from 80% to 0% of the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is expressed as “Al80% → 0%”. The fact that the Al composition of the Al _x3 Ga _(1-x3) N constituting it is made 80% constant is expressed as “Al 80% single film”. Further, in FIG. 3, the change in Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 from 80% to 20%, 30%, 40%, 50% and 70%, respectively, It is expressed in the same notation as in the case of changing to 0%.

The horizontal axis of the graph shown in FIG. 4 indicates that Al _x3 Ga _(1-x3) N constituting the composition change layer 123 from x1 that determines the composition of Al _x1 Ga _(1-x1) N constituting the upper guide layer 122b. The difference x1-y is obtained by subtracting the minimum value y of x3 that determines the composition. The vertical axis of the graph indicates the optical confinement coefficient Γ of the guide layer 122. FIG. 4 is a graph showing the difference x1-y dependency of the light confinement coefficient Γ of the guide layer 122 when the total thickness ΣT of the light emitting layer 121 and the guide layer 122 provided in the nitride semiconductor laser device 1 is 336 nm.

  When the light emitting layer 121 and the guide layer 122 have a total film thickness ΣT of 70 nm or more and 850 nm or less (70 nm ≦ T1 + T2 + T3 ≦ 850 nm), the light confinement coefficient Γ of the guide layer 122 increases as shown in FIG. In particular, when the nitride semiconductor multilayer film 12 has the composition change layer 123 in which the Al composition is changed from 80% to 40%, 50%, or 70%, the Al composition is changed from 80% to 0% or 20%. %, The optical confinement coefficient Γ of the guide layer 122 becomes higher than that in the case of having the composition change layer 123 changed to any one of%. The light confinement coefficient Γ is a ratio at which light emitted from the light emitting layer 121 is confined in the guide layer 122. For this reason, light leakage from the guide layer 122 to the composition change layer 123, the nitride semiconductor layer 14, and the lower cladding layer 13 is suppressed. Thereby, the nitride semiconductor laser device 1 can achieve high output.

  Further, when the nitride semiconductor multilayer film 12 has a structure in which the Al composition of the composition change layer 123 is changed from 80% to 30%, and the light emitting layer 121 and the guide layer 122 have a total film thickness ΣT of 536 nm. The laser oscillation of the nitride semiconductor laser element 1 could not be confirmed. Thus, the laser oscillation of the nitride semiconductor laser device 1 could not be confirmed because the structure of the lower cladding layer 13 and the structure of the upper cladding layer constituted by the composition change layer 123 and the nitride semiconductor layer 14 are asymmetric. This is because light leaks to the lower cladding layer 13 side. Further, in the nitride semiconductor laser element 1, even if the total film thickness ΣT of the light emitting layer 121 and the guide layer 122 satisfies the relationship of the above formula (12), the Al composition of the composition change layer 123 is the above formula (5). The laser does not oscillate when the relationship of) is not satisfied.

  When the nitride semiconductor multilayer film 12 includes the composition change layer 123 in which the Al composition is changed from 80% to 40%, 50%, or 70%, the guide layer with respect to the film thickness of the upper guide layer 122b. The characteristics of the optical confinement coefficient Γ of 122 are almost the same. For this reason, even if there is variation in the Al composition in the composition change layer 123 from 80%, the light confinement coefficient Γ of the guide layer 122 is approximately the same value if the variation is within the range of 40% to 70%. It becomes. For this reason, the dispersion | variation in the individual difference of the output of the nitride semiconductor laser element 1 is reduced. The total film thickness ΣT of the light emitting layer 121 and the guide layer 122 may satisfy the formula (12), and may be 70 nm or more and smaller than 600 nm.

  If the optical confinement factor is 0.020 or less, light leakage to the lower cladding layer 13 increases. For this reason, the optical confinement coefficient Γ is preferably higher than 0.020. When the change in the Al composition of the composition change layer 123 is 80% to 30%, the total film thickness ΣT of the light emitting layer 121 and the guide layer 122 is 536 nm, and the optical confinement coefficient Γ is 0.019, nitriding The fact that the semiconductor laser device 1 does not oscillate also indicates that the optical confinement coefficient Γ is preferably higher than 0.020.

  Further, when the nitride semiconductor multilayer film 12 has a structure that changes the Al composition of the composition change layer 123 from 80% to 50%, and the light emitting layer 121 and the guide layer 122 have a structure with a total film thickness ΣT of 836 nm. The laser oscillation of the nitride semiconductor laser element 1 could not be confirmed. Thus, the laser oscillation of the nitride semiconductor laser device 1 could not be confirmed because the structure of the lower cladding layer 13 and the structure of the upper cladding layer constituted by the composition change layer 123 and the nitride semiconductor layer 14 are asymmetric. This is because light leaks to the lower cladding layer 13 side.

Incidentally, as described above, in the laminated structure of the nitride semiconductor laser device, which is a hypothesis of simulation in which each characteristic shown in FIG. 3 is obtained, _{x1 of} Al _x1 Ga _(1-x1) N constituting the guide layer 122 is 0. .5, and _{x2 of} Al _x2 Ga _(1-x2) N constituting the well layer 121a is 0.3. Moreover, the maximum value z of the Al composition of Al _x3 Ga _(1-x3) N of each composition change layer 123 plotted in FIG. 3 is 0.8 (Al composition ratio 80%). For this reason, all the characteristics shown in FIG. 3 satisfy the above-described formula (4) (x2 <x1 <z). Therefore, satisfying the relationship of Expression (4) improves the optical confinement coefficient Γ of the guide layer 122 and suppresses light leakage from the guide layer 122 to the composition change layer 123, the nitride semiconductor layer 14, and the lower cladding layer 13. Is done.

Also, the white circles in FIG. 3 indicate characteristics when the minimum value y of the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is 0.4 (Al composition ratio 40%). The white triangle mark in FIG. 3 indicates the case where the minimum value y of the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is 0.5 (Al composition ratio 50%). The characteristics are shown. For this reason, the characteristics of the white circles and the characteristics of the white triangles in FIG. 3 satisfy the above-described formula (5) (−1 <x1−y <0.2). Therefore, satisfying the relationship of Expression (4) improves the optical confinement coefficient Γ of the guide layer 122 and suppresses light leakage from the guide layer 122 to the composition change layer 123, the nitride semiconductor layer 14, and the lower cladding layer 13. Is done.

The shaded square marks in FIG. 3 indicate characteristics when the minimum value y of the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is 0 (Al composition ratio 0%). The hatched rhombus marks shown in FIG. 3 indicate the characteristics when the minimum value of the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is 0.2 (Al composition ratio 20%). The white diamonds shown in FIG. 3 are characteristics when the minimum value of the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is 0.3 (Al composition ratio 30%). Is shown. For this reason, the shaded square mark, the shaded diamond mark, and the open diamond mark in FIG. 3 indicate characteristics when the above formula (6) (x2 <y) is not satisfied. On the other hand, the remaining characteristics in FIG. 3 indicate that the minimum value of the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is 0.4 (Al composition ratio 40%) or more and 3 (Al composition ratio 30%), and is a characteristic when the relationship of the above formula (6) (x2 <y) is satisfied. Thus, by satisfying the relationship of Expression (6), the optical confinement coefficient Γ is further improved, and light leakage from the guide layer 122 to the composition change layer 123, the nitride semiconductor layer 14, and the lower cladding layer 13 is further increased. It is further suppressed. Note that when the composition change layer 123 was changed from 80% to 0%, 10%, and 20% in the Al composition of Al _x3 Ga _(1-x3) N, laser oscillation did not occur.

As shown in FIG. 4, the optical confinement coefficient Γ of the guide layer 122 increases rapidly when the difference x1-y is in the range of 0.5 to 0.2, and in the range where the difference x1-y is smaller than 0.2. It becomes constant at 0.026. Thus, the total film thickness ΣT of the light emitting layer 121 and the guide layer 122 is a film thickness in a range (336 nm in FIG. 4) that satisfies the relationship of Expression (12), and the difference x1-y is smaller than 0.2. (That is, satisfying the relationship of Expression (5)), the light confinement coefficient Γ of the guide layer 122 can be improved and stabilized. In addition, since the maximum value of the minimum value y of x3 of the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is 1, Al _x1 Ga _(1-x1) constituting the upper guide layer 122b. _{) When} x1 of the Al composition of N is 0, which is the minimum value, the relationship of “−1 <x1-y” in the formula (5) is satisfied.

The horizontal axis of the graph shown in FIG. 5 indicates the total film thickness ΣT [nm] of the light emitting layer 121 and the guide layer 122, and the vertical axis of the graph indicates the threshold current density of the nitride semiconductor laser device 1. Jth [kA / cm ² ] is shown. The white diamonds in FIG. 5 indicate the case where the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is changed from 80% to 30% (ie, y = 0.3 and z = 0.8) is a relationship between the total thickness ΣT of the light emitting layer 121 and the guide layer 122 and the threshold current density Jth [kA / cm ² ] of the nitride semiconductor laser device 1. The white circles in FIG. 5 indicate the case where the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is changed from 80% to 40% (ie, y = 0.4 and z = 0.8) is a relationship between the total thickness ΣT of the light emitting layer 121 and the guide layer 122 and the threshold current density Jth [kA / cm ² ] of the nitride semiconductor laser device 1. The white triangles shown in FIG. 5 indicate the case where the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is changed from 80% to 50% (ie, y = 0.5 and z = 0.8) is a relationship between the total thickness ΣT of the light emitting layer 121 and the guide layer 122 and the threshold current density Jth [kA / cm ² ] of the nitride semiconductor laser device 1. 5 indicates the case where the Al composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123 is changed from 80% to 70% (that is, y = 0.7 and z = 0). 8) shows the relationship between the film thickness T3 of the upper guide layer 122b and the threshold current density Jth [kA / cm ² ] of the nitride semiconductor laser device 1. In FIG. 5, the change in the Al composition in the composition change layer 123 is represented by the same notation as in FIG.

  On the premise that the nitride semiconductor multilayer film 12 has a film thickness in the range shown in Formula (12), the total thickness of the light emitting layer 121 and the guide layer 122 is 70 nm to 330 nm (70 nm ≦ T1 + T2 + T3 ≦ 330 nm). When ΣT is provided, the threshold current density Jth becomes low as shown in FIG. For this reason, since the nitride semiconductor laser element 1 has the composition change layer 123, the drive current can be reduced, so that the output can be increased.

In the nitride semiconductor laser element 1, if the threshold current density Jth is high, element destruction due to heat generation occurs before laser oscillation occurs. Therefore, the threshold current density Jth of the nitride semiconductor laser element 1 may be 1000 kA / cm ² or less, 300 kA / cm ² or less, and further 200 kA / cm ² or less. As described above, in the laminated structure of the nitride semiconductor laser element 1 that is a simulation hypothesis for obtaining the characteristics shown in FIG. 5, the film thickness T2 of the light emitting layer 121 is assumed to be 36 nm. Therefore, the nitride semiconductor laser element 1 having a structure in which the total film thickness ΣT of the light emitting layer 121 and the guide layer 122 is smaller than 40 nm cannot be manufactured. As shown in FIG. 5, when the total film thickness ΣT of the light emitting layer 121 and the guide layer 122 is smaller than 70 nm, the threshold current density Jth of the nitride semiconductor laser device 1 tends to increase. The increase rate of the threshold current density Jth of the nitride semiconductor laser device 1 in the range where the total film thickness ΣT of the light emitting layer 121 and the guide layer 122 is in the range from 70 nm to 40 nm is that the total film thickness ΣT of the light emitting layer 121 and the guide layer 122 is The threshold current density Jth at 40 nm is not so large as to exceed 1000 kA / cm ² . For this reason, the nitride semiconductor laser element 1 can prevent element destruction due to heat generation before laser oscillation by satisfying the relationship of the expression (12).

  Further, for example, when the light emitting layer 121 has a film thickness T2 of 5 nm or more and 50 nm or less (20 nm ≦ T2 ≦ 50 nm), and the nitride semiconductor multilayer film 12 has a film thickness in the range shown in Formula (12). To do. In this case, the light emission efficiency is improved and the carrier leakage to the nitride semiconductor layer 14 is suppressed, so that the output of the nitride semiconductor laser device 1 can be increased.

  The composition change layer 123 has a film thickness Tc (0 <Tc <500 nm) that is greater than 0 and less than 500 nm, for example. Further, when the film thickness Tc of the composition change layer 123 is 500 nm or more, the light emitting layer 121 emits light because the absolute film thickness of the low composition region (eg, 0 ≦ x3 <x1) including the upper region 123b increases. A large amount of the absorbed light is absorbed in the low composition region, and laser oscillation is suppressed by an increase in internal loss. In order to obtain the polarization doping effect of the composition change layer 123, the film thickness Tc of the composition change layer 123 needs to be larger than 0 nm. Furthermore, when the film thickness Tc of the composition change layer 123 is 500 nm or more, the resistance of the composition change layer 123 is increased, and the driving voltage of the nitride semiconductor laser device 1 is increased. For this reason, the film thickness Tc of the composition change layer 123 is preferably in the range of at least larger than 0 and smaller than 500 nm.

  The composition change layer 123 may have a film thickness Tc (0 nm ≦ Tc ≦ 500 nm) of, for example, 0 nm or more and 500 nm or less. The film thickness Tc of the composition change layer 123 may be greater than 100 nm and 300 nm or less (0 nm <Tc ≦ 300 nm). By setting the film thickness Tc of the composition change layer 123 within this range, the threshold current density Jth is reduced by improving the optical confinement efficiency and the internal efficiency ηi of the nitride semiconductor laser device 1, and the composition change layer by polarization doping. The improvement of the hole density in 123 can be achieved at the same time. Thereby, the nitride semiconductor laser device 1 can achieve high output.

When the distance from the region 123d where the Al composition in the composition change layer 123 is the same as the Al composition of the lower guide layer 122a to the uppermost end of the nitride semiconductor multilayer film 12 is T4, the nitride semiconductor multilayer film 12 is It has the laminated structure which satisfy | fills the relationship of Formula (13).
0.6 <(T1 + T2 + T3) / T4 <3.5 (13)
Here, the uppermost end of the nitride semiconductor multilayer film 12 is the surface of the composition change layer 123 in contact with the nitride semiconductor layer 14.

  When the nitride semiconductor multilayer film 12 has a laminated structure that satisfies the relationship of the formula (13), the light emitted from the light emitting layer 121 escapes from the guide layer 122 to the nitride semiconductor layer 14, that is, oozes out. Is suppressed. The distance T4 from the region 123d to the uppermost end of the nitride semiconductor multilayer film 12 may satisfy, for example, the relationship of Expression (13) and may be greater than 0 and smaller than 200 nm (0 <T4 <200 nm), for example. This further suppresses the light emitted from the light emitting layer 121 from leaking from the guide layer 122 to the nitride semiconductor layer 14. Further, the distance T4 from the region 123d to the uppermost end of the nitride semiconductor multilayer film 12 may satisfy, for example, the relationship of the expression (13) and may be larger than 0 and smaller than 100 nm (0 <T4 <100 nm). . Thereby, it is further suppressed that the light emitted from the light emitting layer 121 exudes from the guide layer 122 to the nitride semiconductor layer 14. As a result, the nitride semiconductor laser element 1 can reduce the threshold current density Jth and increase the output.

Here, the relationship between the distance T4 from the region 123d of the composition change layer 123 to the uppermost end of the nitride semiconductor multilayer film 12 and the total film thickness ΣT of the light emitting layer 121 and the guide layer 122 will be described with reference to FIG. Will be described with reference to FIG. The horizontal axis of the graph shown in FIG. 6 indicates the ratio ΣT / T4 (T1 + T2 + T3 / T4) of the total film thickness ΣT of the light emitting layer 121 and the guide layer 122 with respect to the distance T4, and the vertical axis of the graph indicates the optical confinement of the guide layer 122. The coefficient Γ is shown. The horizontal axis of the graph shown in FIG. 7 indicates the Al _x4 Ga _(1-) that forms the lower cladding layer 13 from the minimum value y of x3 that determines the composition of Al _x3 Ga _(1-x3) N that constitutes the composition change layer 123. _x4) A difference y-x4 obtained by subtracting x4 that determines the composition of N is shown. The vertical axis of the graph indicates the optical confinement coefficient Γ of the guide layer 122. The horizontal axis of the graph shown in FIG. 8 indicates the ratio ΣT / T4 of the total film thickness ΣT with respect to the distance T4, and the vertical axis of the graph indicates the threshold current density Jth [kA / cm ² ] of the nitride semiconductor laser device 1. ing.

  Simulation software SiLENSe Laser Edition was used for the simulation to obtain the characteristics shown in FIGS. Further, the nitride semiconductor laser device stack structure, which is a hypothesis of simulation, is the same as the stack structure for obtaining the characteristics shown in FIGS. However, in FIGS. 6 and 8, the values of the thickness T1 of the lower guide layer 122a and the thickness T3 of the upper guide layer 122b are appropriately changed, and the nitride semiconductor multilayer film is changed from the region 123d of the light emitting layer 121T2 and the composition change layer 123. The value of the distance T4 to the top end of 12 was fixed. In FIG. 7, the value of the total film thickness ΣT of the light emitting layer 121 and the guide layer 122 is fixed at 336 nm, and the Al composition of the composition change layer 123 is changed from 80% to 30%. The composition of the composition change layer 123 in the characteristics shown by the white diamonds and white circles shown in FIG. 6 is the composition of the composition change layer 123 in the characteristics shown by the white diamonds and white circles shown in FIG. Since they are the same as each other, the description is omitted. Further, the composition of the composition change layer 123 in the characteristics shown by the white diamonds and white circles shown in FIG. 8 is the composition change layer 123 in the characteristics shown by the white diamonds and white circles shown in FIG. Since the composition of each is the same, description thereof is omitted.

  The ratio ΣT / T4 (0.6 ≦ (T1 + T2 + T3) /T4≦3.9) of the total film thickness ΣT with respect to the distance T4 in which the composition change layer 123, the light emitting layer 121, and the guide layer 122 are 0.6 or more and 3.4 or less. ), The optical confinement coefficient Γ of the guide layer 122 becomes larger than 0.020 as shown in FIG. For this reason, in the nitride semiconductor laser element 1, light leakage from the guide layer 122 to the composition change layer 123, the nitride semiconductor layer 14, and the lower cladding layer 13 is suppressed by satisfying the relationship of Expression (13). Thereby, the nitride semiconductor laser device 1 can achieve high output.

  When the nitride semiconductor multilayer film 12 has the composition change layer 123 in which the Al composition is changed from 80% to 40%, 50%, or 70%, the light of the guide layer 122 with respect to the ratio ΣT / T4 The characteristics of the confinement factor Γ are almost the same. For this reason, even if there is variation in the Al composition in the composition change layer 123 from 80%, the light confinement coefficient Γ of the guide layer 122 is approximately the same value if the variation is within the range of 40% to 70%. It becomes. For this reason, the dispersion | variation in the individual difference of the output of the nitride semiconductor laser element 1 is reduced.

As shown in FIG. 7, the optical confinement factor Γ of the guide layer 122 increases rapidly when the difference z−x4 is in the range of 0 to 0.1, and is 0. 0 in the range where the difference z−x4 is larger than 0.2. It becomes constant at 026. As described above, _x4 for determining the composition of Al _x4 Ga _(1-x4) N constituting the lower cladding layer 13 and _x3 for determining the composition of Al _x3 Ga _(1-x3) N constituting the composition change layer 123. When the difference z−x4 with respect to the maximum value z is 0 or more and less than 0.4, the optical confinement coefficient Γ of the guide layer 122 is improved. In particular, when the difference z−x4 is 0.2 or more, the optical confinement coefficient Γ of the guide layer 122 can be stabilized.

Further, the ratio ΣT / T4 (0.6 ≦ (T1 + T2 + T3) / T4) of the total film thickness ΣT with respect to the distance T4 in which the ratio of the composition change layer 123 to the light emitting layer 121 and the guide layer 122 is 0.6 or more and 3.3 or less. If it has ≦ 3.3), the threshold current density Jth is lower than 300 kA / cm ² as shown in FIG. For this reason, the nitride semiconductor laser element 1 has a ratio ΣT / T4 in which the composition change layer 123, the light emitting layer 121, and the guide layer 122 satisfy the relationship of Expression (13), so that the drive current can be reduced. Output can be achieved. Further, when the composition change layer 123 has a structure in which the Al composition is changed from 80% to 30%, and the nitride laminate 10 has a structure of a ratio ΣT / T4 of 4.1, the nitride semiconductor laser element 1 Did not oscillate.

Next, the relationship between the threshold current density Jth of the nitride semiconductor laser element 1 and the film thickness of the nitride semiconductor layer 14 will be described with reference to FIG. The horizontal axis of the graph shown in FIG. 9 indicates the film thickness T5 (nm) of the nitride semiconductor layer 14, and the vertical axis of the graph indicates the threshold current density Jth (kA / cm ² ) of the nitride semiconductor laser device 1. Show.

Simulation software SiLENSe Laser Edition was used for the simulation to obtain the characteristics shown in FIG. The laminated structure of the nitride semiconductor laser element, which is a hypothesis for simulation, is the same as that of the nitride semiconductor laser element 1 shown in FIGS. More specifically, the substrate 11 was made of AlN having a thickness of 2 μm, and the lower cladding layer was made of a layer having an Al composition of Al _x4 Ga _(1-x4) N of 60% (that is, x4 = 0.6). Further, the lower guide layer 122a and the upper guide layer 122b are layers in which the Al composition of Al _x1 Ga _(1-x1) N is 50% (that is, x1 = 0.5). The light emitting layer 121 has a double quantum well structure of “barrier layer / well layer 121a / barrier layer / well layer 121a / barrier layer”, and the well layer 121a has an Al composition of Al _x2 Ga _(1-x2) N. Is 30% (ie, x3 = 0.3), and the barrier layer is a layer in which the Al composition of AlGaN is 50%. The nitride semiconductor layer 14 is a layer in which the Al composition of Al _x5 Ga _(1-x5) N is 0% (that is, x3 = 0), that is, a layer formed of GaN.

In this simulation, each of the first region 131 and the second region 132 of the lower cladding layer 13 is an n-type nitride layer having a concentration of 3.0 × 10 ¹⁸ cm ⁻³ of silicon (Si) as an impurity, Each film thickness was 1000 nm. The lower guide layer 122a and the upper guide layer 122b are non-doped nitride layers, respectively, and have a thickness of 150 nm. The two well layers 121a are non-doped nitride layers and have a thickness of 2.5 nm. The three barrier layers were non-doped nitride layers, and the film thickness was 10.0 nm. The composition change layer 123 is a p-type nitride layer having a concentration of 3.0 × 10 ¹⁹ cm ⁻³ of magnesium (Mg) as an impurity and has a thickness of 150 nm. The nitride semiconductor layer 14 was a p-type nitride layer having a concentration of 3.0 × 10 ²⁰ cm ⁻³ of magnesium (Mg) as an impurity, and the film thickness was changed in the range of 0 nm to 30 nm. In each layer, the electron mobility was 100 mc ² · Vs, and the hole mobility was 10 cm ² · Vs. The dislocation density was 1 × 10 ⁹ cm ⁻² . Furthermore, the growth surface was 0001.

  In this simulation, the laser characteristics are such that the length of the guide layer 122 is 1000 μm, the ridge width (that is, the width of the nitride semiconductor layer 14) is 4 μm, the reflectance at the emission side end face 122Sa is 0.2, The reflectance at the facing end surface 122Sb was set to 0.9.

The thickness T5 of the nitride semiconductor layer 14 is larger than 0 and smaller than 30 nm. In the present embodiment, the nitride semiconductor layer 14 is formed of, for example, p-type GaN (x5 = 0 in Al _x5 Ga _(1-x5) N). The nitride semiconductor laser device 1 requires an upper cladding layer composed of the composition change layer 123 and the nitride semiconductor layer 14 in order to guide the light emitted from the light emitting layer 121 in the guide layer 122. Further, when the thickness T5 of the nitride semiconductor layer 14 is larger than 30 nm, the nitride semiconductor layer 14 absorbs light emitted from the light emitting layer 121. Absorption of light by the nitride semiconductor layer 14 becomes significant when the nitride semiconductor layer 14 is formed of GaN rather than Al _x5 Ga _(1-x5) N. For this reason, the film thickness T5 of the nitride semiconductor layer 14 is preferably in the range of at least 0 and less than 30 nm. By setting the film thickness T5 of the nitride semiconductor layer 14 within this range, the threshold current density Jth can be reduced. Further, the nitride semiconductor laser element 1 did not oscillate in the structure in which the thickness T5 of the nitride semiconductor layer 14 was 30 nm.

  Next, the method for manufacturing the nitride semiconductor laser element 1 according to the present embodiment will be explained. In order to form the nitride semiconductor laser element 1, a wafer having a predetermined thickness in a range longer than 50 μm and shorter than 10000 μm, for example, is prepared. The nitride semiconductor laser device 1 includes a nitride semiconductor layer that finally becomes the lower cladding layer 13, a nitride semiconductor layer that finally becomes the lower guide layer 122a, and a nitride that finally becomes the light emitting layer 121 on the wafer. A nitride semiconductor layer, a nitride semiconductor layer that finally becomes the upper guide layer 122b, a nitride semiconductor layer that finally becomes the composition change layer 123, and a nitride semiconductor layer that finally becomes the nitride semiconductor layer 14 A physical semiconductor laminate is formed. Next, the p-type electrode 15 and the n-type electrode 16 are formed. Thereafter, a plurality of nitride laminates 10 are formed on the wafer by dry etching and wet etching a part of the semiconductor laminate in a predetermined shape. Thereafter, the nitride semiconductor laser device 1 is completed by cutting the wafer at a predetermined position to separate the nitride laminate 10 into individual pieces. After that, the packaged laser diode is completed by covering and fixing the nitride semiconductor laser element 1 with a package.

When forming the nitride semiconductor layer that finally becomes the composition change layer 123, the composition is controlled in the film thickness direction so that, for example, the composition of Al _x3 Ga _(1-x3) N changes continuously or stepwise. A nitride semiconductor layer is formed.

  The nitride laminate 10 may be formed by cleaving the nitride semiconductor laminate instead of dry etching and wet etching.

  As described above, the nitride semiconductor laser element 1 according to the present embodiment can achieve high output by reducing the threshold current density Jth. In addition, the nitride semiconductor laser element 1 can improve the optical confinement coefficient Γ of the guide layer 122 and suppress internal loss (that is, optical loss in the guide layer 122). In addition, the nitride semiconductor laser element 1 can improve the optical confinement coefficient Γ of the guide layer 122 and improve the external differential quantum efficiency. Here, the external differential quantum efficiency is the light emission efficiency (%) of the laser, and is obtained by dividing the number of laser photons by the number of input electrons (the number of laser photons / the number of input electrons). Furthermore, the nitride semiconductor laser device 1 can improve the slope efficiency by improving the optical confinement coefficient Γ of the guide layer 122. Here, the slope efficiency is obtained by dividing the light emission output (W) by the input current (A) (light emission output / input current).

[Second Embodiment]
A nitride semiconductor laser device according to a second embodiment of the present invention will be described with reference to FIGS. Since the nitride semiconductor laser device according to the present embodiment has the same external configuration as the nitride semiconductor laser device 1 according to the first embodiment, the description will be made using the same reference numerals.

  As shown in FIG. 1, the nitride semiconductor laser element 1 according to the present embodiment is similar to the nitride semiconductor laser element 1 according to the first embodiment described above, and includes a substrate 11 and a nitride semiconductor provided above the substrate 11. The stacked film 12 includes a p-type electrode 15 and an n-type electrode 16 that inject current into the nitride semiconductor stacked film 12. The nitride semiconductor multilayer film 12 includes a lower guide layer 122a, a light emitting layer 121 stacked on the lower guide layer 122a and having a well layer 121a, an upper guide layer 122b stacked on the light emitting layer 121, and an upper portion The composition change layer 123 is laminated on the guide layer 122b and the composition is changed continuously or stepwise in the film thickness direction. The refractive index of the composition change layer 123 increases continuously or stepwise as the distance from the upper guide layer 122b increases.

  The nitride semiconductor laser device 1 according to the present embodiment includes the lower cladding layer 13 formed in the lower layer of the lower guide layer 122a and the nitride semiconductor layer 14 formed in the upper layer of the composition change layer 123. The p-type electrode 15 is formed on the nitride semiconductor layer 14, and the n-type electrode 16 is formed on the lower cladding layer 13. Although illustration is omitted, a laser diode packaged by the nitride semiconductor laser element 1 and a package covering the nitride semiconductor laser element 1 is configured.

The refractive index of the lower guide layer 122a is n1, the band gap is E1, the refractive index of the well layer 121a is n2, the band gap is E2, the refractive index of the upper guide layer 122b is n3, and the band gap is E3. When the refractive index and the band gap range of 123 are changed from n4 to n5 and from E4 to E5, the nitride semiconductor multilayer film 12 has a composition satisfying the relationship of the following expressions (14) and (15). Yes.
n4 <n1 (14)
-0.5 <E5-E1 <1.3 (15)

  By satisfying the relationship of the formula (14), the light emitted from the light emitting layer 121 is reflected by using the refractive index difference at the interface between the upper guide layer 122b and the composition change layer 123, and the light is reflected in the guide layer 122. Can be trapped. Further, by satisfying the relationship of the formula (15), it is possible to suppress the influence of the light emission in the light emitting layer 121 being absorbed in the region where the band gap of the composition change layer 123 is the smallest, thereby reducing the internal loss. The threshold for laser oscillation can be lowered. In the composition change layer 123, the band gap at the portion where the refractive index is n4 is E4, and the band gap at the portion where the refractive index is n5 is E5.

As shown in FIG. 2, when the thickness of the lower guide layer 122a is T1, the thickness of the light emitting layer is T2, the thickness of the upper guide layer 122b is T3, and the thickness of the composition change layer 123 is Tc, The nitride semiconductor multilayer film 12 has a thickness that satisfies the relationship of the following formula (16).
40 nm <T1 + T2 + T3 <600 nm (16)

In the present embodiment, since the light emitting layer 121 has a single quantum well configuration, the thickness of the well layer 121 a is also the thickness of the light emitting layer 121. For this reason, the nitride semiconductor multilayer film 12 has a film thickness that satisfies the relationship of Expression (16). Since the nitride semiconductor multilayer film 12 has a film thickness in the range indicated by the formula (16), the nitride semiconductor laser device 1 can achieve high output.
The

As described above, in the nitride semiconductor laser element 1 according to the first and second embodiments, the composition of Al _x3 Ga _(1-x3) N that constitutes the composition change layer 123 is further away from the upper guide layer 122b. X3 for determining the value is changed from the maximum value z to the minimum value y. The nitride semiconductor laser element 1 is based on the composition structure of the composition change layer 123, and the thickness of the guide layer 122 is appropriately set. Further, the nitride semiconductor laser element 1 has an Al composition larger than that of the guide layer in the entire composition change layer 123. The nitride semiconductor laser device 1 according to the first embodiment and the second embodiment includes the composition change layer 123 for performing polarization doping, and confines light in the guide layer 122 while maintaining the effect of this polarization doping. be able to.

  As mentioned above, although embodiment of this invention was described referring an accompanying drawing, this invention is not limited to this embodiment. It is obvious that various modifications or modifications can be conceived by those skilled in the art without departing from the combination of the embodiments and within the scope of the claims. It is understood that it belongs to the technical scope of the invention.

DESCRIPTION OF SYMBOLS 1 Nitride semiconductor laser element 10 Nitride laminated body 11 Substrate 11S Laminated surface 12 Nitride semiconductor laminated film 13 Lower clad layer 14 Nitride semiconductor layer 15 P-type electrode 16 N-type electrode 121 Light emitting layer 121a Well layer 122 Guide layer 122a Lower part Guide layer 122b Upper guide layer 122Sa Emission side end face 122Sb Opposing end face 123 Composition change layer 123a Lower area 123b Upper area 123c Intermediate area 123d Area 131 First area 132 Second areas T1, T2, T3, Tc Film thickness T4 Distance

Claims (8)

A light emitting layer having a lower guide layer formed of Al _x1 Ga _(1-x1) N, a well layer formed on the lower guide layer and formed of Al _x2 Ga _(1-x2) N, and the light emitting layer And an upper guide layer made of Al _x1 Ga _(1-x1) N, and an upper guide layer formed by laminating Al _x3 Ga _(1-x3) N on the upper guide layer. A nitride semiconductor multilayer film including a composition change layer in which the Al composition of the Al _x3 Ga _(1-x3) N decreases continuously or stepwise as the distance from the layer increases;
A p-type electrode and an n-type electrode for injecting current into the nitride semiconductor multilayer film,
The minimum value of x3 of the Al _x3 Ga _(1-x3) N is y, and the maximum value is z,
When the thickness of the lower guide layer is T1, the thickness of the light emitting layer is T2, and the thickness of the upper guide layer is T3,
The nitride semiconductor multilayer film is
0 ≦ x1 ≦ 1, 0 ≦ x2 ≦ 1, 0 ≦ x3 ≦ 1, x2 <x1 <z and -1 <x1-y <0.2
A nitride semiconductor laser device having a film thickness satisfying a relationship of 40 nm <T1 + T2 + T3 <600 nm. When the distance from the region where the Al composition in the composition change layer is the same as the Al composition of the lower guide layer to the uppermost end of the nitride semiconductor multilayer film is T4,
The nitride semiconductor laser element according to claim 1, wherein the nitride semiconductor multilayer film has a multilayer structure that satisfies a relationship of 0.6 <(T1 + T2 + T3) / T4 <3.5. The nitride semiconductor laser element according to claim 1, wherein a composition change rate of Al in the composition change layer is greater than 0.1% / nm. In the case where the well layer is formed of the Al _x2 Ga _(1-x2) N,
The nitride semiconductor laser element according to any one of claims 1 to 3, wherein the well layer and the composition change layer have a composition satisfying a relationship of x2 <y. A lower clad layer formed under the lower guide layer and having n-type Al _x4 Ga _(1-x4) N;
The difference between x4 that determines the composition of the Al _x4 Ga _(1-x4) N and the maximum z of x3 that determines the composition of the Al _x3 Ga _(1-x3) N is 0 or more and 0.4 The nitride semiconductor laser device according to any one of claims 1 to 4, wherein the nitride semiconductor laser device is smaller. A nitride semiconductor layer formed of Al _x5 Ga _(1-x5) N and laminated on the composition change layer;
The Al _x5 Ga _(1-x5) N has a composition satisfying a relationship of 0 ≦ x5 ≦ y,
The nitride semiconductor laser element according to any one of claims 1 to 5, wherein the nitride semiconductor layer has a thickness of 0 nm or more and less than 30 nm. The nitride semiconductor laser element according to any one of claims 1 to 6, wherein the light emitting layer can emit ultraviolet light having a wavelength of 360 nm or less. A lower guide layer, a light emitting layer stacked on the lower guide layer and having a well layer, an upper guide layer stacked on the light emitting layer, and a continuous or staircase composition stacked on the upper guide layer A nitride semiconductor multilayer film having a composition change layer that is changed in the film thickness direction,
A p-type electrode and an n-type electrode for injecting current into the nitride semiconductor multilayer film,
The refractive index of the lower guide layer is n1, the band gap is E1, the film thickness is T1,
The refractive index of the well layer is n2, the band gap is E2,
The film thickness of the light emitting layer is T2,
The refractive index of the upper guide layer is n3, the band gap is E3, the film thickness is T3,
The ranges in which the refractive index and band gap of the composition change layer change are n4 to n5 and E4 to E5,
When the film thickness of the composition change layer is Tc,
The nitride semiconductor multilayer film is
a composition satisfying the relationship of n4 <n1, -0.5 <E5-E1 <1.3,
And a film thickness satisfying a relationship of 40 nm <T1 + T2 + T3 <600 nm,
The nitride semiconductor laser element, wherein a refractive index of the composition change layer increases continuously or stepwise as the distance from the upper guide layer increases.

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