Vertical-cavity surface-emitting laser device

Abstract

To provide a vertical cavity surface emitting laser element having improved life characteristics by suppressing deterioration caused by current concentration or the like of a surface emitting laser element having a convex portion on the p-side semiconductor layer side.SOLUTION: A vertical cavity surface emitting laser element includes a first light reflecting film 1, a nitride semiconductor laminate 5 in which an n-side semiconductor layer 2, an active layer 3, and a p-side semiconductor layer 4 having a convex portion 4a are laminated in this order on the upper surface of the first light reflecting film 1, a translucent p electrode 6 that contacts the upper surface of the convex portion 4a and extends to the surface 4b around the convex portion, and a second light reflecting film 8 placed on the p electrode 6, and the height of the convex portion 4a is smaller than the thickness of the p electrode 6.SELECTED DRAWING: Figure 1B

Description

[Technical field]

[0001] The present disclosure relates to vertical cavity surface emitting laser devices. [Background technology]

[0002] 2. Description of the Related Art Research has been conducted on laser elements that use nitride semiconductors and function as vertical-cavity surface-emitting lasers. For example, a structure has been proposed in which current confinement is achieved by forming an insulating film on a semiconductor laminate. Patent Document 1 describes a structure in which an insulating film having an opening is formed on the surface of a p-type semiconductor layer, and a transparent electrode such as ITO is formed on the surface of the p-type semiconductor layer exposed at the opening. Patent Document 2 describes a structure in which a mesa structure is provided as the p-type semiconductor layer of a surface-emitting laser element having a GaN-based semiconductor laminate, and the mesa structure is surrounded by an insulating film having an opening. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-035541 A [Patent Document 2] JP 2018-129385 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a surface-emitting laser element having a convex portion on a p-type semiconductor layer as a current confinement structure, the thickness of the electrode itself formed thereon varies due to the convex portion, and the electrode on the side surface of the convex portion in particular tends to be thin. Unlike an edge-emitting laser element, in a vertical-cavity surface-emitting laser element, the electrode that runs along the side surface of the convex portion becomes the current path, so when a current flows through the thin film portion where the electrode is thin in this way, the sheet resistance tends to be high. In addition, due to the undulations of the convex portion, the electrode above it has a bent shape. Current concentration tends to occur at the bent portion of the electrode, which can lead to the destruction of the electrode. [Means for solving the problem]

[0005] The present disclosure includes the following inventions. A first light reflecting film; a nitride semiconductor laminate in which an n-side semiconductor layer, an active layer, and a p-side semiconductor layer having a convex portion are laminated in this order on an upper surface of the first light reflecting film; a light-transmitting p-electrode in contact with an upper surface of the protrusion and extending to a surface surrounding the protrusion; a second light reflecting film disposed on the p-electrode; The height of the protrusion is smaller than the thickness of the p-electrode. Effect of the Invention

[0006] According to the vertical cavity surface emitting laser element of the present disclosure, it is possible to provide a vertical cavity surface emitting laser element having an improved life characteristic with respect to a surface emitting laser element having a convex portion on the p-side semiconductor layer side. [Brief description of the drawings]

[0007] [Figure 1A] 1 is a schematic plan view for explaining a structure of a vertical cavity surface emitting laser element according to an embodiment of the present invention; [Figure 1B] 1B is a schematic cross-sectional view taken along line IA-IA' in FIG. 1A. [Figure 1C]1B is a schematic cross-sectional view of a main portion showing a laminated structure in a current confinement structure of the vertical cavity surface emitting laser element of FIG. 1A. [Figure 1D] 1D is a schematic cross-sectional view showing an enlarged view of the vicinity Q of the convex portion in FIG. 1C. [Figure 1E] FIG. 1E is a further enlarged schematic cross-sectional view of the vicinity of the convex portion in FIG. 1D. [Diagram 2] FIG. 11 is a schematic cross-sectional view showing a main part of a modified example of a vertical cavity surface emitting laser element. [Diagram 3] 13 is a graph showing the change over time in normalized optical output when the vertical cavity surface emitting laser element of Test Example 1 was subjected to continuous oscillation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings as appropriate. However, the embodiments described below are intended to embody the technical ideas of the present disclosure, and unless otherwise specified, the present disclosure is not limited to the following. Furthermore, the contents described in one embodiment or example can be applied to other embodiments or examples. The size, thickness, positional relationship, etc. of the members shown in each drawing may be exaggerated to clarify the explanation. In this specification, the direction from the n-side semiconductor layer to the p-side semiconductor layer in a laminate of nitride semiconductors constituting a vertical cavity surface emitting laser device is referred to as "upward."

[0009] 1A and 1B, a vertical cavity surface emitting laser element according to an embodiment of the present disclosure includes a first optical reflection film 1, a nitride semiconductor stack 5, a light-transmitting p-electrode 6, and a second optical reflection film 8. The stack 5 is disposed on the upper surface of the first optical reflection film 1, and an n-side semiconductor layer 2, an active layer 3, and a p-side semiconductor layer 4 having a protrusion 4a are stacked in this order. The p-electrode 6 is disposed in contact with the upper surface of the protrusion 4a and extends to a surface 4b around the protrusion. The second optical reflection film 8 is disposed on the p-electrode 6. In the vertical cavity surface emitting laser element having such a configuration, the height of the protrusion is smaller than the thickness of the p-electrode, so that partial thinning of the p-electrode and current concentration caused by the protrusion of the p-side semiconductor layer can be suppressed, and destruction of the p-electrode due to current concentration can be suppressed. As a result, the life characteristics can be improved. Instead of or in addition to such a relationship between the height of the protrusion and the thickness of the p-electrode, the inclination angle of the side surface of the protrusion can be set to 45 degrees or less. This makes it possible to suppress partial thinning of the p-electrode and current concentration caused by the protrusion of the p-side semiconductor layer, and destruction of the p-electrode due to current concentration. As a result, the life characteristics can be improved.

[0010] (1st light reflective film 1) The first light reflecting film 1 is composed of, for example, a semiconductor multilayer film and a dielectric multilayer film. A light reflecting film can be obtained by alternately stacking two or more films with different refractive indices. The semiconductor multilayer film can be a nitride semiconductor layer, for example, an AlInGaN compound semiconductor. Specifically, AlN, InN, GaN, AlGaN, InGaN, AlInN, and AlInGaN can be mentioned. Among them, a combination of GaN and AlInN that is lattice-matched therewith is preferable. In addition, the dielectric laminated film can be, for example, an oxide, nitride, or fluoride of Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, B, Ti, or the like. Specifically, SiO2 / Nb2O5, SiO2 / Ta2O5, and SiO2 / Al2O3 can be mentioned.

[0011] In order to obtain the intended reflectance, the first light reflecting film 1 can appropriately select the material constituting each layer, the film thickness, the number of layers, and the like. For example, the thickness of each layer constituting the laminated film is λ / (4n) (where λ is the oscillation wavelength of the laser, and n is the refractive index of the medium constituting each layer), and can be appropriately set according to the refractive index n of the material used at the oscillation wavelength λ. Specifically, it is preferable to set it to an odd multiple of λ / (4n). For example, in a light emitting device with an oscillation wavelength λ of 450 nm, when the first light reflecting film 1 is made of GaN / AlInN, the thickness of each layer can be 40 nm to 70 nm. The number of layers in the laminated film can be appropriately set according to the intended characteristics. The number of layers in the laminated film can be 2 or more, for example, 5 to 100 layers. The total thickness of the first light reflecting film 1 can be, for example, 0.08 μm to 7 μm. The size and shape of the first light reflecting film 1 can be appropriately designed as long as it covers the light emitting portion of the laser element. The first light reflecting film 1 can be formed, for example, on a substrate 11 for semiconductor growth or on top of this with an underlayer or the like therebetween by a method known in the art, as described later.

[0012] (Nitride semiconductor stack 5) The nitride semiconductor laminate 5 is disposed on the first light reflecting film 1. The nitride semiconductor laminate 5 is configured by, for example, laminating an n-side semiconductor layer 2 made of an AlInGaN compound semiconductor, an active layer 3 made of an AlInGaN compound semiconductor, and a p-side semiconductor layer 4 made of an AlInGaN compound semiconductor in this order on the first light reflecting film 1. Examples of AlInGaN compound semiconductors include AlN, InN, GaN, AlGaN, InGaN, AlInN, and AlInGaN. The n-side semiconductor layer 2 is a single layer or a multilayer, and has one or more n-type layers doped with n-type impurities, such as Si. The active layer 3 has a laminated structure in which quantum well layers made of InGaN and barrier layers made of GaN are alternately laminated. The number of layers can be appropriately set according to the desired characteristics. In addition to GaN, InGaN or the like having a lower In composition than the InGaN of the quantum well layer can also be used as the barrier layer. The p-side semiconductor layer 4 can have a p-side cladding layer and a p-side contact layer disposed thereon. The p-side contact layer is a layer doped with p-type impurities, such as Mg. The p-side cladding layer can be a layer doped with p-type impurities at a lower concentration than the p-side contact layer, or an undoped layer. In this case, the p-side contact layer is the top layer of the p-side semiconductor layer 4. The thicknesses of the n-side semiconductor layer 2, the active layer 3, and the p-side semiconductor layer 4 can be set appropriately. The total film thickness from the upper surface of the first light reflecting film 1 to the lower surface of the second light reflecting film 8 described later is set to an integer multiple of λ / (2n) so that a standing wave occurs between them. It is preferable to arrange the active layer 3 so that the strongest part of the standing wave is located, and the light-transmitting p-electrode 6 described later so that the weakest part of the standing wave is located. By setting in this way, the threshold current can be reduced. The threshold current means the minimum current required for laser oscillation.

[0013] The nitride semiconductor laminate 5 has a convex portion 4a on the upper surface of the p-side semiconductor layer 4. The convex portion 4a has a shape that is convex upward. The upper surface of this convex portion 4a functions as a current injection region, and the portion directly below the current injection region becomes a light emitting portion. The shape of the convex portion 4a in a plan view may be a circle, an ellipse, a polygon, or the like, but is preferably a circle in consideration of injecting a more uniform current into the nitride semiconductor laminate 5. The size of the upper surface of the convex portion 4a may be, for example, a diameter or a length of one side of 2 μm to 12 μm. The side surface of the convex portion 4a may be perpendicular to the upper surface of the convex portion 4a, but is preferably inclined as shown in FIGS. 1D and 1E. The inclination angle (α in FIG. 1E) of the convex portion 4a may be 60 degrees or less, preferably 45 degrees or less, more preferably 40 degrees or less, and even more preferably 30 degrees or less. The inclination angle α may be greater than 0 degrees, 1 degree or more, or 5 degrees or more. The inclination angle α is the angle of the side of the convex portion 4a with respect to a virtual plane extending from the surface 4b around the convex portion toward the center of the convex portion, as shown in FIG. 1E. In the cross-sectional view of FIG. 1E, the virtual plane extending from the surface 4b around the convex portion toward the center of the convex portion is shown by one virtual straight line (hereinafter referred to as virtual line A). As shown in FIG. 1E, when the connection portion between the surface 4b around the convex portion and the convex portion 4a is a curved surface, the side of the convex portion 4a is represented by one virtual straight line (hereinafter referred to as virtual line B) in the cross-sectional view, and the angle of the virtual line B with respect to the virtual line A is defined as the inclination angle α. Note that in FIG. 1E, there are two types of angles formed by the virtual line A and the virtual line B, but the inclination angle α of the convex portion 4a is the angle formed by the virtual line A and the portion of the virtual line B that faces upward from the intersection point of the virtual line A and the virtual line B. Here, the surface 4b around the protrusion refers to the flat surface of the p-side semiconductor layer 4 among the surfaces around the protrusion 4a, as shown in FIG. 1B and the like. The protrusion 4a is preferably shaped like a frustum, for example. By inclining the protrusion 4a at an angle within the above range, it is possible to further suppress the thinning of the p-electrode 6, which will be described later. In addition, it is possible to make the undulations of the p-electrode 6 near the protrusion 4a gentler, and it is possible to reduce current concentration at the bending points of the p-electrode 6 around the protrusion 4a. In this way, it is possible to define the light-emitting portion by forming the protrusion 4a on the upper surface of the p-side semiconductor layer 4.Furthermore, by forming the protrusions 4a, a difference in refractive index can be provided between the resonator portion and its surrounding area, enabling light confinement in the lateral direction.

[0014] The height of the protrusions 4a (D in FIG. 1D) is, for example, 100 nm or less, or 50 nm or less. In particular, it is preferable that the height D of the protrusion 4a is smaller than the thickness of the p-electrode 6 described later. The height D of the protrusion 4a is preferably 0.8 times or less, more preferably 0.5 times or less, and even more preferably 0.3 times or less, of the thickness of the p-electrode. The height D of the protrusion 4a may be 0.05 times or more of the thickness of the p-electrode 6. In this way, by making the height D of the protrusion 4a smaller than the thickness of the p-electrode 6, the variation in the thickness of the p-electrode 6 formed thereon, which is caused by the protrusion, can be reduced. This makes it possible to suppress partial thinning. In addition, in the p-electrode 6 around the protrusion 4a, the shortest current path can be easily secured, and the current concentration in the p-electrode 6 at the bending point can be alleviated. As a result, it is possible to reduce the destruction of the p-electrode 6 and improve the life characteristics. In addition, the second light reflection film 8 formed on the protrusion 4a, which is described later, can be arranged more flatly on the upper surface of the protrusion 4a, that is, directly above the current injection region X, as shown in FIG. 1C. This makes it possible to effectively inject carriers into the light-emitting portion. As a result, the laser light can be generated more stably in the light emitting section. Note that the height D of the protrusion 4a here refers to the shortest distance between an imaginary plane extending from the surface 4b around the protrusion toward the center of the protrusion 4a and the upper surface of the protrusion 4a, for example, as shown in FIG. 1D.

[0015] Moreover, the height D of the protrusions 4a is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 15 nm or less. By setting the height to 30 nm or less, it is possible to reduce the scattering loss of light on the surface of the protrusions 4a, and it is possible to reduce the threshold current of the vertical cavity surface emitting laser element. Moreover, the height D of the protrusions 4a is preferably 1 nm or more or 3 nm or more. By setting the height to 1 nm or more, it becomes easier to perform current confinement.

[0016] The upper surface of the protrusion 4a is preferably formed by the p-side contact layer that is doped with the p-type impurity at the highest concentration among the p-side semiconductor layer 4. The entire protrusion 4a may be formed only by the p-side contact layer, but the protrusion 4a preferably has a layer doped with the p-type impurity at a lower concentration than the p-side contact layer or is undoped. Such a lightly doped or undoped layer is preferably arranged on the surface 4b around the protrusion. In this case, the lightly doped or undoped layer is also arranged on the lower part of the protrusion 4a. Such a lightly doped or undoped layer is arranged, for example, as a p-side cladding layer. In other words, the p-type impurity concentration of the layer that constitutes the upper surface of the protrusion 4a is preferably higher than the p-type impurity concentration of the surface 4b around the protrusion. This allows the upper surface of the protrusion 4a to make good contact with the translucent p-electrode 6. Furthermore, even if the surface 4b around the protrusion is in contact with the p-electrode 6, the current injected into that part can be reduced compared to the protrusion 4a. Therefore, the current can be effectively injected from only the upper surface of the protrusion 4a. The p-type impurity concentration of the layer constituting the surface 4b around the protrusion is, for example, 1×10 17 cm -3 ~1×10 19 cm -3 The p-type impurity concentration of the layer constituting the upper surface of the protrusion 4a can be, for example, 5×10 19 cm -3 ~5×10 21 cm -3 It can be said that: In order to form a flat second light reflecting film 8, which will be described later, it is preferable that the upper surface of the protrusion 4a is a flat surface. Moreover, it is preferable that the surface 4b around the protrusion of the p-side semiconductor layer 4 is also a flat surface. Here, the flat upper surface of the protrusion 4a means, for example, that the arithmetic mean roughness of the upper surface of the protrusion 4a is 0.1 nm to 2 nm. Moreover, the flat surface 4b around the protrusion means, for example, that the arithmetic mean roughness of the surface 4b around the protrusion is 0.1 nm to 2 nm. As an example of current confinement, the upper surface of the protrusion 4a is formed by a p-side contact layer doped with a high concentration of p-type impurities, and the surface 4b around the protrusion is formed by a layer doped with a low concentration of p-type impurities, as described above. With this configuration, current is preferentially injected from the p-side contact layer, and current confinement is possible without providing an insulating film between the p-electrode 6 and the p-side semiconductor layer 4, that is, while keeping the surface 4b around the protrusion flat.

[0017] 1B, in the nitride semiconductor stack 5, it is preferable that on the surface 4b around the protrusion, i.e., on the side of the p-side semiconductor layer 4, the p-side semiconductor layer 4, the active layer 3, and the n-side semiconductor layer 2 are partly removed in the thickness direction to partially expose the n-side semiconductor layer 2. In other words, it is preferable that the n-side semiconductor layer 2 is exposed on the side of the top surface of the nitride semiconductor stack 5 in the n-side semiconductor layer 2, i.e., on the side of the p-side semiconductor layer 4. This makes it possible to arrange the p-electrode and the n-electrode that supply current to the laser element on the same side of the stack. After forming the nitride semiconductor stack 5, the protrusion 4a can be formed and a part of the n-side semiconductor layer 2 can be exposed by using a known method such as photolithography and etching.

[0018] (p electrode 6) The p-electrode 6 is an electrode for injecting a current from the protrusion 4a of the p-side semiconductor layer 4, and is an electrode in contact with at least the upper surface of the protrusion 4a. The p-electrode 6 extends to the side surface of the protrusion 4a, and may extend to the surface 4b around the protrusion. For example, the p-electrode 6 is disposed from the upper surface of the protrusion 4a, passing through the side surface of the protrusion 4a, to the p-side semiconductor layer 4 around the protrusion 4a.

[0019] The p-electrode 6 is preferably in contact only with the p-side semiconductor layer 4, and more preferably in contact with the flat p-side semiconductor layer 4, particularly around the convex portion 4a. The planar area of ​​the upper surface of the p-electrode 6 can be, for example, larger than the planar area of ​​the upper surface of the convex portion 4a, and can be set to a size such that its outer edge is located inside the outer edge of the upper surface of the p-side semiconductor layer 4 in plan view. This makes it easier to form the p-pad electrode 9p so as not to overlap the second light reflecting film 8 in plan view.

[0020] The p-electrode 6 is a conductive member formed of a light-transmitting material having a transmittance of 60% or more, more preferably 90% or more, for light of the peak wavelength of the laser light oscillated by the vertical-cavity surface-emitting laser element. Examples of light-transmitting materials include transparent conductive materials whose base material is an oxide such as indium-tin oxide (ITO) or indium-zinc oxide (IZO). A specific example is ITO. A thinner thickness can reduce light absorption by the p-electrode 6, but increases resistance, so the thickness can be appropriately adjusted in consideration of the balance between these two. The thickness of the p electrode 6 is, for example, 100 nm or less, preferably 60 nm or less, more preferably 35 nm or less, and even more preferably 30 nm or less. The thickness of the p electrode 6 may be 5 nm or more. The thickness of the p electrode 6 is, for example, 5 nm to 100 nm, preferably 10 nm or more and 60 nm or less, more preferably 15 nm or more and 35 nm or less, and even more preferably 20 nm or more and 30 nm or less. When the thickness of the p electrode 6 is within the above range, light absorption by the p electrode 6 can be reduced, and the threshold current can be reduced. The difference between the thickness of the p-electrode 6 and the height of the protrusion 4a can be, for example, 10 nm or more, and preferably 20 nm or more. This can further reduce current concentration at the bending points of the p-electrode 6 around the protrusion 4a. The difference between the thickness of the p-electrode 6 and the height of the protrusion 4a can be, for example, 100 nm or less. The thickness of the p-electrode 6 may be 1.25 times or more, preferably 2 times or more, and more preferably 3 times or more, the height of the protrusion 4a. This makes it possible to further reduce current concentration at the bending points of the p-electrode 6 around the protrusion 4a. The thickness of the p-electrode 6 may be 20 times or less the height of the protrusion 4a.

[0021] (Second light reflective film 8) The second light reflecting film 8 is disposed on the p-electrode 6. It may be disposed only on the upper surface of the protrusion 4a, or may extend from the upper surface of the protrusion 4a to the side of the protrusion 4a, that is, may be disposed on at least a part of the surface 4b around the protrusion. In particular, when the second light reflecting film 8 is disposed on the surface 4b around the protrusion, it is preferable that the surface 4b around the protrusion is flat. With such an arrangement, the second light reflecting film 8 can be formed flat directly above the current injection region or directly above and around it. Therefore, the second light reflecting film 8 can ensure a uniform reflectance in a relatively wide area of ​​the dielectric multilayer film without being affected by the unevenness of the base. As a result, it becomes possible to easily control the shape of the oscillating laser light to stabilize it. At least a part of the surface 4b around the protrusions is, for example, a region surrounding the protrusions 4a, and the diameter or length of one side is about 10% to 50% larger than the diameter or length of one side of the protrusions 4a. The area of ​​the upper surface of the protrusions 4a is preferably small to achieve current constriction, while the plane area of ​​the second light reflecting film 8 is easier to form if it is relatively large. For this reason, the second light reflecting film 8 is preferably provided not only on the upper surfaces of the protrusions 4a but also in a region including at least a part of the surface 4b around the protrusions.

[0022] The second light reflecting film 8 can be configured to include a dielectric multilayer film. The second light reflecting film 8 can be configured similarly to the dielectric multilayer film exemplified in the first light reflecting film 1 described above. Examples include SiO2 / Nb2O5, SiO2 / Ta2O5, and SiO2 / Al2O3. The thickness of each layer is preferably λ / (4n) (where λ is the oscillation wavelength of the laser, and n is the refractive index of the medium constituting each layer). The number of layers can be appropriately set according to the intended characteristics. Specifically, when the second light reflecting film 8 is made of SiO2 / Nb2O5 or the like, each layer has a thickness of 40 nm to 70 nm. The number of layers of the laminated film can be 2 or more, for example, 5 to 20 layers. The total thickness of the second light reflecting film 8 can be, for example, 0.08 μm to 2.0 μm, and can be 0.6 μm to 1.7 μm. The second light reflecting film 8 is preferably disposed apart from the insulating film 7 described later. In other words, the second light reflecting film 8 is preferably disposed so as not to overlap the insulating film 7 described later in a plan view. This allows the second light reflecting film 8 to be disposed with fewer steps.

[0023] (Other materials) (Insulating film 7) The vertical cavity surface emitting laser device 10A may further include an insulating film 7. The insulating film 7 is preferably disposed apart from the upper surface of the protrusion 4a. This allows the p-electrode 6 to have fewer steps. In addition, the second light reflecting film 8 to have fewer steps. The insulating film 7 preferably covers at least a part of the surface 4b around the protrusion 4a of the p-side semiconductor layer 4. In other words, the insulating film 7 is preferably formed at least on the upper surface of the nitride semiconductor stack 5 so as not to overlap with the protrusion 4a and to have an opening on the protrusion 4a or on the protrusion 4a and its periphery in a plan view. This allows current injection from other than the protrusion 4a to be reduced. The insulating film 7 may also be disposed on a part or all of the side surface of the nitride semiconductor or on a part of the upper surface of the exposed n-side semiconductor layer 2. The thickness of the insulating film 7 can be set appropriately. The insulating film 7 is preferably disposed at a distance from the second light reflecting film 8. In other words, the insulating film 7 and the second light reflecting film 8 are preferably disposed so as not to overlap each other in a plan view. This allows the second light reflecting film 8 to be disposed more flatly directly above the upper surface of the protrusion 4a. The insulating film 7 is made of SiO X SiN based materials, such as SiN Y based materials, SiO X N Y It can be formed from inorganic materials such as Ta2O5, ZrO2, AlN, Al2O3, and Ga2O3.

[0024] (p-pad electrode 9p, n-electrode 9n) The vertical cavity surface emitting laser element 10A preferably further includes a p-pad electrode 9p electrically connected to the p-electrode 6 on the side of the protrusion 4a. Also, it is preferable that an n-electrode 9n is disposed which is electrically connected to the exposed n-side semiconductor layer 2. With this configuration, it is not necessary for the current to pass through the first light reflecting film 1 as a current path, so there is no need to dope the first light reflecting film 1 with n-type impurities, and the first light reflecting film 1 can be made to have a higher reflectance. The p-pad electrode 9p and the n-electrode 9n may be formed of any conductive material that is normally used as an electrode in the field. Examples include Ti / Pt / Au and Ti / Rh / Au. The p-pad electrode 9p is preferably arranged in a shape that surrounds the outer periphery of the protrusion 4a. This allows current to be injected more uniformly from the p-pad electrode 9p through the p-electrode 6 into the p-side semiconductor layer 4. The p-pad electrode 9p is preferably arranged apart from the second light reflecting film 8. In other words, the p-pad electrode 9p is preferably arranged so as not to overlap the second light reflecting film 8 in a planar view. In this way, the p-pad electrode 9p is not arranged directly below the second light reflecting film 8, so that the second light reflecting film 8 directly above the current injection region can be more easily flattened. The n-electrode 9n and the p-pad electrode 9p may be formed in a single layer structure using the same or different materials, may be formed in the same laminate structure using the same material, or may be formed in different laminate structures using different materials. When the n-electrode 9n and the p-pad electrode 9p are formed in the same laminate structure using the same material, the n-electrode 9n and the p-pad electrode 9p can be formed in the same process.

[0025] (Substrate 11) Since the nitride semiconductor stack 5 is usually stacked on a semiconductor growth substrate, the vertical cavity surface emitting laser element may have a semiconductor growth substrate 11. When the first optical reflection film 1 is made of a nitride semiconductor, the first optical reflection film 1 is first formed on the substrate 11, and the stack 5 is then formed thereon. Alternatively, after the stack 5 is formed on the substrate 11, the semiconductor growth substrate may be removed from the stack 5, and the first optical reflection film 1 may be formed on the surface of the stack 5 exposed by the removal. Examples of the semiconductor growth substrate 11 include substrates of nitride semiconductors (such as GaN), sapphire, SiC, Si, and the like.

[0026] (Heat dissipation board 12) The above-mentioned vertical cavity surface emitting laser element may be a vertical cavity surface emitting laser element 10B bonded to a heat dissipation substrate 12 as shown in FIG. 2. Examples of the heat dissipation substrate 12 include a semiconductor substrate made of a semiconductor such as AlN or SiC, a metal substrate made of a single metal or a composite of two or more metals. For example, a substrate having insulating AlN ceramic as a base material and a plurality of metal films 15 formed on the surface thereof may be used as the heat dissipation substrate 12. The metal films 15 are electrically connected to the p-pad electrode 9p and the n-electrode 9n, respectively. When it is not necessary to electrically connect both the p-electrode and the n-electrode to the heat dissipation substrate 12, such as when the p-pad electrode 9p and the n-electrode 9n are disposed with the laminate 5 interposed therebetween or when the side of the first light reflecting film 1 is bonded to the heat dissipation substrate 12, a conductive substrate such as a metal substrate may be used as the heat dissipation substrate 12. The thickness of the heat dissipation substrate 12 may be, for example, about 50 μm to 500 μm. The heat dissipation substrate 12 can be formed by any method commonly used in the art.

[0027] (Anti-reflective film 14) The above-mentioned vertical cavity surface emitting laser element 10B emits laser light from the first light reflecting film 1 side, but an anti-reflection film 14 may be disposed on the surface of the first light reflecting film 1 opposite to the laminate 5, or on the surface of the substrate 11 opposite to the laminate 5 when the above-mentioned substrate 11 is included. The anti-reflection film 14 may be made of the same material as the dielectric multilayer film exemplified for the above-mentioned first light reflecting film 1. By making the number of layers and the thickness of each layer different from the light reflecting film, a film having an anti-reflection function can be formed. Examples of the anti-reflection film include SiO2 / Nb2O5, SiO2 / Ta2O5, and SiO2 / Al2O3. The thickness of the anti-reflection film may be, for example, 0.4 μm.

[0028] (Method of manufacturing a vertical cavity surface emitting laser element) The above-mentioned vertical cavity surface emitting laser element can be manufactured as follows. For example, a nitride semiconductor stack 5 having an n-side semiconductor layer 2, an active layer 3, and a p-side semiconductor layer 4 having a protruding portion 4a in this order is formed, a light-transmitting p-electrode 6 is formed in contact with the upper surface of the protruding portion 4a and extending to the surface 4b around the protruding portion, a second light reflecting film 8 is formed on the p-electrode 6, the protruding portion 4a is formed by removing a part of the upper surface of the p-side semiconductor layer 4, and the p-electrode 6 is formed so that the height of the protruding portion 4a is smaller than the thickness of the p-electrode 6. In addition, among the above-mentioned methods, instead of forming the p-electrode 6 so that the height of the protruding portion 4a is smaller than the thickness of the p-electrode 6, the protruding portion 4a may be formed so that the inclination angle α of the side surface of the protruding portion 4a is 45 degrees or less. Alternatively, a p-electrode 6 that satisfies both of these may be formed. The first light reflecting film 1 is formed, for example, before forming the stack 5. That is, a substrate 11 for semiconductor growth may be prepared, and the first light reflecting film 1 may be formed on the substrate 11. Thereafter, the n-side semiconductor layer 2, the active layer 3, and the p-side semiconductor layer 4 are laminated in this order on the upper surface of the first light reflecting film 1. Furthermore, a part of the upper surface of the p-side semiconductor layer 4 is removed to form a protruding portion 4a. This allows the nitride semiconductor laminate 5 to be formed. The protruding portion 4a can be formed, for example, by removing a part of the p-side semiconductor layer so as to partially leave the protruding portion 4a using dry etching or the like. When forming the nitride semiconductor laminate 5, the surface of the n-side semiconductor layer 2 may be exposed by removing a part of the p-side semiconductor layer 4 and the active layer 3 before or after the formation of the protruding portion 4a. Thereafter, a light-transmitting p-electrode 6 is formed in contact with the upper surface of the protruding portion 4a and extending to the surface 4b around the protruding portion. Subsequently, the insulating film 7 may be formed to cover the sides and the like of the protrusion 4a of the p-side semiconductor layer 4. The insulating film 7 may be formed so as to cover the outer periphery of the p-electrode 6 and so as to partly cover the p-electrode 6, for example. After forming the insulating film 7, the p-pad electrode 9p and the n-electrode 9n are formed. When the p-pad electrode 9p is formed in a ring shape larger than the protrusion 4a and surrounding the upper surface of the protrusion 4a and its periphery, a current can be more uniformly injected from the p-pad electrode 9p through the p-electrode 6 to the p-side semiconductor layer 4. A second light reflecting film 8 is formed on the p-electrode 6, from the upper surface of the protrusion 4a to at least a part of the surface 4b surrounding the protrusion. The second light reflecting film 8 is preferably disposed so as to be separated from the insulating film 7 and not to come into contact with it. Thereafter, as shown in FIG. 2, the surface of the semiconductor growth substrate opposite to the first light reflecting film 1 can be thinned to form a thinned substrate. At this time, the semiconductor growth substrate may be completely removed. The thinning or removal can be performed using a polishing method, an etching method, or the like known in the art. An anti-reflection film 14 may be formed on the surface of the substrate opposite to the first light reflecting film 1. When the substrate 11 is completely removed, the anti-reflection film 14 may be formed on the surface of the first light reflecting film 1. Furthermore, the obtained laminate 5 can be bonded to the heat dissipation substrate 12. The bonding layer 13 can be arranged so as to be bonded to the p-pad electrode 9p and the n-electrode 9n, respectively, and to be bonded to the metal film 15 of the heat dissipation substrate 12, respectively. The area between the heat dissipation substrate 12 and the obtained laminate 5, that is, the area other than the area in which the bonding layer 13 is disposed in the laminate 5, may be left hollow, or may be filled with an insulating heat dissipation member or the like. The bonding of the laminate 5 to the heat dissipation substrate 12 may be performed before the thinning of the substrate 11 and / or the formation of the anti-reflection film 14. The formation of the first light reflection film 1 may be performed after the formation of the second light reflection film 8. For example, a part or all of the substrate 11 can be removed, and the first light reflection film 1 can be formed on the surface exposed by the removal.

[0029] Test Example 1 As shown in Figs. 1A and 1B, a laser element was formed as a vertical cavity surface emitting laser element 10A, which includes a substrate 11 made of GaN, a laminated body 5 of nitride semiconductors, a light-transmitting p-electrode 6 (30 nm thick) made of ITO, a second light reflecting film 8 (SiO2 / Nb2O5, 76.9 / 47.8 nm thick, 15.5 pairs) including a dielectric laminated film, and an insulating film 7 (SiO2, 100 nm thick). The laminated body 5 includes a first light reflecting film 1 (AlInN / GaN, 51.2 nm / 46.6 nm thick, 50 pairs), an n-side semiconductor layer 2 (Si-doped GaN), an active layer 3 (GaN / InGaN), and a p-side semiconductor layer 4 (undoped GaN, Mg-doped AlGaN, and Mg-doped GaN) laminated in this order. The p-side semiconductor layer 4 has a convex portion 4a (inclination angle: 27 degrees, height: 8 nm, diameter: 5 µm, planar shape: circular). The p-electrode 6 is in contact with the upper surface of the protrusion 4a and extends to the surface 4b around the protrusion. The second light reflecting film 8 extends to the side of the protrusion 4a and is disposed on the p-electrode 6. The insulating film 7 is spaced apart from the second light reflecting film 8 and covers at least a part of the surface 4b around the protrusion of the p-side semiconductor layer 4. In a part of the laminate 5, the p-side semiconductor layer 4 and the active layer 3 are removed to expose the n-side semiconductor layer 2, and an n-electrode 9n and a p-pad electrode 9p (Ti / Pt / Au, 1.5 nm / 200 nm / 500 nm) are formed on the surface and the p-electrode 6. When a current (4 mA) was injected into the vertical cavity surface emitting laser device 10A having such a configuration and the device was operated continuously at room temperature, laser light with a peak wavelength of 443 nm was emitted downward in FIG. 1B. Furthermore, a life test was conducted in an aging apparatus by injecting a current (4 mA) into the vertical cavity surface emitting laser element 10A at room temperature for continuous operation. The result of the life characteristic from the life test is shown in FIG. 3. In this disclosure, the life characteristic means the degree to which the laser element maintains its emission intensity when a constant current is injected into the laser element for continuous operation. From the result in FIG. 3, it can be seen that the vertical cavity surface emitting laser element 10A maintained an output close to 70% of the output at the initial operation start even after 1000 hours. It was also confirmed that laser oscillation occurred even after 1000 hours of operation. [Explanation of symbols]

[0030] 1 First light reflective film 2 n-side semiconductor layer 3 Active layer 4 p-side semiconductor layer 4a Convex part 4b Surface surrounding the convex part 5. Laminate 6p electrode 7. Insulating Film 8 Second light reflective film 9n n electrode 9p p-pad electrode 10A, 10B Vertical-cavity surface-emitting laser element 11 Substrate 12 Heat dissipation board 13 Bonding layer 14 Anti-reflection coating 15 Metal Film

Claims

1. A first light reflecting film; a nitride semiconductor layer structure in which an n-side semiconductor layer, an active layer, and a p-side semiconductor layer having a protrusion are stacked in this order on an upper surface of the first light reflecting film; a light-transmitting p-electrode in contact with an upper surface of the protrusion and extending to a surface surrounding the protrusion; a second light reflecting film disposed on the p-electrode; the height of the protrusion is smaller than the thickness of the p-electrode, The vertical cavity surface emitting laser element, wherein the protrusion has an inclination angle of 60 degrees or less.

2. A vertical cavity surface emitting laser element as described in claim 1, wherein the p-type impurity concentration of the layer constituting the upper surface of the convex portion is higher than the p-type impurity concentration of the surface surrounding the convex portion.

3. A first light reflective film; a nitride semiconductor layer structure in which an n-side semiconductor layer, an active layer, and a p-side semiconductor layer having a protrusion are stacked in this order on an upper surface of the first light reflecting film; a light-transmitting p-electrode in contact with an upper surface of the protrusion and extending to a surface surrounding the protrusion; a second light reflecting film disposed on the p-electrode; the height of the protrusion is smaller than the thickness of the p-electrode, a p-type impurity concentration of a layer constituting an upper surface of the protrusion is higher than a p-type impurity concentration of a surface surrounding the protrusion.

4. 4. The vertical cavity surface emitting laser element according to claim 1, wherein the second light reflecting film includes a dielectric laminate film and is disposed on the p-electrode so as to extend to a side of the protrusion.

5. 5. The vertical cavity surface emitting laser element according to claim 1, further comprising an insulating film spaced apart from an upper surface of the protrusion and covering at least a portion of a surface of the p-side semiconductor layer surrounding the protrusion.

6. The vertical cavity surface emitting laser device according to claim 5 , wherein the insulating film is spaced apart from the second light reflecting film.

7. 7. The vertical cavity surface emitting laser device according to claim 1, wherein the p-electrode has a thickness of 100 nm or less.

8. 8. The vertical cavity surface emitting laser element according to claim 1, further comprising a p-pad electrode connected to the p-electrode on a side of the protrusion.

9. The vertical cavity surface emitting laser device according to claim 8 , wherein the p-pad electrode is spaced apart from the second light reflecting film.

10. 10. The vertical cavity surface emitting laser device according to claim 1, wherein the first light reflecting film includes a semiconductor multilayer film.

11. the p-side semiconductor layer has a p-side cladding layer and a p-side contact layer disposed on the p-side cladding layer, 11. The vertical cavity surface emitting laser element according to claim 1, wherein the protrusion has the p-side contact layer on an upper surface thereof, and a surface surrounding the protrusion is the surface of the p-side cladding layer.

12. 12. The vertical cavity surface emitting laser element according to claim 1, further comprising a heat dissipation substrate above the second light reflecting film.

13. The p-type impurity concentration of the layer constituting the upper surface of the protrusion is 5×10 19 cm －3 ~5×10 21 cm －3 and The p-type impurity concentration of the layer constituting the surface around the protrusion is 1×10 17 cm －3 ~1×10 19 cm －3 13. The vertical cavity surface emitting laser device according to claim 1, wherein

14. the arithmetic mean roughness of the upper surface of the convex portion is 0.1 nm to 2 nm; 14. The vertical cavity surface emitting laser element according to claim 1, wherein the arithmetic mean roughness of the surface around the convex portion is 0.1 nm to 2 nm.

15. 15. The vertical cavity surface emitting laser element according to claim 1, wherein a difference between a thickness of the p-electrode and a height of the protrusion is 10 nm or more and 100 nm or less.

16. 16. The vertical cavity surface emitting laser element according to claim 1, wherein the thickness of the p-electrode is 1.25 to 20 times the height of the protrusion.

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