Surface-emitting laser element

Abstract

To provide a photonic crystal plane emission layer capable of easily controlling a beam shape with high accuracy and having a high beam stability to a high output.SOLUTION: A plane emission laser device comprises: a light-transmitting substrate; an n-type semiconductor layer; an active layer; a p-type semiconductor layer; a vacancy layer 14P as a photonic crystal layer; a light reflection layer 32 having a refraction surface; and a light-transmitting conductive layer 31 that is provided between the reflection surface and the p-type semiconductor layer. The vacancy layer includes: a diffraction surface as a wave source when diffracting a light existed in the vacancy layer in a direction orthogonal to the vacancy layer; a weakening region where a separation distance d between the diffraction surface and the reflection surface is provided so that a light strength of an interference light generated by an interference of a first diffraction light that is diffracted to a light emission surface side from the diffraction surface, and a second diffraction light reflected by the reflection surface diffracted to a light reflection layer side from the diffraction surface becomes smaller than a light strength of the first diffraction light; and a strengthening region where the separation distance between the diffraction surface and the reflection surface is provided so that the light strength of the interference light becomes larger than that of the first diffraction light.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a surface-emitting laser element, and more particularly to a surface-emitting laser element having a photonic crystal. [Background technology]

[0002] In recent years, development of photonic-crystal surface-emitting lasers using photonic crystals (PC) has been progressing.

[0003] For example, Patent Document 1 discloses a photonic crystal surface emitting laser that has a single lattice photonic crystal and has a high diffraction effect.

[0004] Furthermore, Patent Document 2 discloses a photonic crystal surface-emitting laser that has a multi-lattice photonic crystal layer, has high flatness and crystallinity of the active layer, has high light extraction efficiency, and is capable of oscillating at a low threshold current density and high quantum efficiency.

[0005] Furthermore, Patent Document 3 discloses a vertical cavity light emitting device having a light guide structure including a central region and a peripheral region provided around the central region and having a shorter optical distance between first and second multilayer film reflectors than that of the central region.

[0006] Non-patent document 1 discloses a formulation of the diffracted light of a photonic crystal surface-emitting laser and the profile of the diffracted radiation wave diffracted in the photonic crystal layer and emitted in a direction perpendicular to the photonic crystal layer (FIG. 1, FIG. 4(b)). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Re-tabled publication No. 2018-155710 [Patent Document 2] Japanese Patent Publication No. 2020-045573 [Patent Document 3] Japanese Patent Application Publication No. 2019-208004 [Non-patent literature]

[0008] [Non-Patent Document 1] Y. Liang et al.: Phys.Rev. B vol.84, 195119 (2011) Summary of the Invention [Problem to be solved by the invention]

[0009] In conventional vertical cavity light emitting devices, a light guide layer having regions with different optical paths is provided in the cavity to control the beam, so in order to stably generate high-power single-peak laser light, the light guide layer must be formed taking into consideration the oscillation mode. The same is true when generating and emitting laser light with a multi-peak intensity distribution (for example, Patent Document 3).

[0010] The present invention focuses on controlling the diffracted light diffracted and emitted from the photonic crystal (PC) layer, i.e., the light already emitted, to control the beam shape to a desired shape, rather than controlling the oscillation mode. This makes it possible to control the beam regardless of the laser oscillation mode. In other words, by utilizing light that does not contribute to oscillation, the beam shape can be easily and accurately controlled.

[0011] The present invention has been made with the above points in mind, and aims to provide a photonic crystal surface-emitting laser that can easily and accurately control the beam shape and has excellent beam (transverse mode) stability up to high output power. [Means for solving the problem]

[0012] A surface-emitting laser element according to one embodiment of the present invention comprises: a light-transmitting substrate; an n-type semiconductor layer provided on the substrate; an active layer provided on the n-type semiconductor layer; a p-type semiconductor layer provided on the active layer; a hole layer that is a photonic crystal layer included in the n-type semiconductor layer and has holes that are arranged with two-dimensional periodicity in a plane parallel to the active layer; a light reflecting layer provided on the p-type semiconductor layer and having a reflecting surface; a transparent conductive layer provided between the reflective surface and the p-type semiconductor layer, a light emitting surface on the rear surface of the substrate; the hole layer has a diffraction surface that is a wave source when light standing in the hole layer is diffracted in a direction perpendicular to the hole layer, a weakening region in which a separation distance between the diffracting surface and the reflecting surface is set so that the light intensity of interference light generated by interference between a first diffracted light diffracted from the diffracting surface toward the light emitting surface and a second diffracted light diffracted from the diffracting surface toward the light reflecting layer and reflected by the reflecting surface is smaller than the light intensity of the first diffracted light; The optical element has a constructive region in which the diffraction surface and the reflection surface are spaced apart from each other so that the intensity of the interference light is greater than the intensity of the first diffraction light. [Brief explanation of the drawings]

[0013] [Figure 1A] 1 is a cross-sectional view schematically illustrating an example of the structure of a PCSEL device 10 according to a first embodiment of the present invention. [Figure 1B] 1B is a partially enlarged cross-sectional view schematically showing an air hole layer 14P (photonic crystal layer) of FIG. 1A and air holes 14K arranged in the air hole layer 14P. FIG. [Figure 2A] FIG. 2 is a plan view schematically showing the upper surface of the PCSEL device 10. [Figure 2B] 2 is a cross-sectional view schematically showing a cross section of a hole layer 14P in a plane parallel to the n-side guide layer 14. FIG. [Figure 2C] FIG. 2 is a plan view schematically showing the bottom surface of the PCSEL device 10. [Figure 3] 2 is a diagram illustrating the optical interference layer 31, the optical reflection layer 32, and the interference of diffracted light in the PCSEL device 10 of the first embodiment. FIG. [Figure 4] FIG. 10 is a graph showing slope efficiency η SE relative to αv / αp. [Figure 5] FIG. 10 is a diagram showing the dependence of slope efficiency η SE on phase difference θ when Ag and Pd are used for the reflective metal layer. [Figure 6] FIG. 10 is a diagram showing the calculation results of the electric field amplitude of a radiation wave that is emitted in the vertical direction (±z direction) after light propagating in the x-axis direction within the air hole layer 14P is diffracted by the air hole layer. [Figure 7] FIG. 10 is a diagram showing the relationship between the slope efficiency η SE and the thickness of the interference layer with respect to the phase difference θ. [Figure 8] FIG. 10 is a schematic cross-sectional view showing a modified example of the first embodiment. [Figure 9] 10A and 10B are diagrams schematically showing a cross section of a PCSEL device 50 according to a second embodiment, the intensity of interference light, and the beam shape. [Figure 10] FIG. 10 is a diagram showing the phase difference (θ) dependence of the thickness of the interference layer for the central region R1 where the light reflecting layer 32(1) is Pd (R=0.45). [Figure 11] 10A and 10B are diagrams schematically showing a cross section of a PCSEL device 60 according to a third embodiment, the intensity of interference light, and the beam shape. DETAILED DESCRIPTION OF THE INVENTION

[0014] In the following, preferred embodiments of the present invention will be described, but these may be modified and combined as appropriate. In the following description and accompanying drawings, substantially the same or equivalent parts are designated by the same reference numerals.

[0015] [First embodiment] 1. Structure of photonic crystal surface-emitting laser (a) Device structure A photonic crystal surface-emitting laser (hereinafter also referred to as PCSEL) is an element that has a resonator layer in a direction parallel to the semiconductor light-emitting structure layers (n-side guide layer, light-emitting layer, p-side guide layer) that constitute the light-emitting element, and emits coherent light in a direction perpendicular to the resonator layer.

[0016] Meanwhile, while distributed Bragg reflector (DBR) lasers are known, photonic crystal surface-emitting lasers (PCSELs) differ from DBR lasers in the following respects: In a photonic crystal surface-emitting laser (PCSEL), light waves propagating in a plane parallel to the photonic crystal layer are diffracted by the diffraction effect of the photonic crystal to form a two-dimensional resonance mode, and are also diffracted in a direction perpendicular to the parallel plane. In other words, in a photonic crystal surface-emitting laser, the light extraction direction is perpendicular to the resonance direction (in a plane parallel to the photonic crystal layer).

[0017] 1A is a cross-sectional view schematically illustrating an example of the structure of a photonic crystal surface-emitting laser device (hereinafter also referred to as a PCSEL device) 10 according to a first embodiment of the present invention. As shown in FIG. 1A, a semiconductor structure layer 11 is formed on a light-transmitting substrate 12. The semiconductor layers are stacked perpendicular to the central axis CX of the semiconductor structure layer 11.

[0018] The semiconductor structure layer 11 is made of a hexagonal nitride semiconductor. In this embodiment, the semiconductor structure layer 11 is made of, for example, a GaN-based semiconductor.

[0019] More specifically, a semiconductor structure layer 11 consisting of a plurality of semiconductor layers is formed on a substrate 12, in this order: an n-clad layer (first clad layer of a first conductivity type) 13, an n-side guide layer (first guide layer) 14 which is a guide layer provided on the n-side, a light distribution adjustment layer 23, an active layer (ACT) 15, a p-side guide layer (second guide layer) 16 which is a guide layer provided on the p-side, an electron barrier layer (EBL: Electron Blocking Layer) 17, a p-clad layer (second clad layer of a second conductivity type) 18, and a p-contact layer 19. Note that, although a case where the first conductivity type is n-type and the second conductivity type which is the opposite conductivity type to the first conductivity type is p-type will be described, the first conductivity type and the second conductivity type may be p-type and n-type, respectively.

[0020] The substrate 12 is a GaN single crystal substrate whose primary surface is the +c plane, which is the {0001} plane with Ga atoms arranged on the outermost surface. While the substrate 12 is not limited to this, an just-aligned substrate or, for example, a substrate whose primary surface is offset by approximately 1° in the m-axis direction is preferred. For example, a substrate offset by approximately 1° in the m-axis direction can achieve mirror-finish growth under a wide range of growth conditions.

[0021] The substrate surface (back surface, light emission surface) on which the light emission region 20L is provided, facing the main surface, is the "-c" plane, which is the (000-1) plane with N atoms arranged on the outermost surface. The -c plane is resistant to oxidation and is therefore suitable as a light extraction surface.

[0022] The composition, thickness, and other configurations of each semiconductor layer will be explained below, but these are merely examples and can be modified as appropriate.

[0023] The n-clad layer 13 is, for example, an n-type Al layer having an Al composition of 4%. 0.04 Ga 0.96 This is the N layer (thickness: 2 μm).

[0024] The n-side guide layer 14 is made up of a lower guide layer 14A, an air-hole layer 14P which is a photonic crystal layer (PC layer), and a buried layer 14B.

[0025] The n-side guide layer 14 is, for example, n-type GaN (layer thickness 360 nm). The lower guide layer 14A of the n-side guide layer 14 is n-type GaN (layer thickness 200 nm). The air-hole layer 14P has a layer thickness (or the depth of the air holes 14K) of 90 nm. The buried layer 14B is n-type GaN (layer thickness 90 nm).

[0026] The light distribution adjustment layer 23 is made of undoped In 0.03 Ga 0.97 This is an N layer (layer thickness: 50 nm). The light distribution adjustment layer 23 functions as an adjustment layer for adjusting the coupling efficiency (optical field) between light and the hole layer 14P.

[0027] The active layer 15, which is a light-emitting layer, is a multiple quantum well (MQW) layer having, for example, two quantum well layers. The barrier layer and quantum well layer of the MQW are GaN (layer thickness 6.0 nm) and InGaN (layer thickness 3.0 nm), respectively. The emission wavelength of the active layer 15 is 435 nm.

[0028] The p-side guide layer 16 is composed of a p-side guide layer (1) 16A and a p-side guide layer (2) 16B. The p-side guide layer (1) 16A is an undoped In 0.02 Ga 0.98 The p-side guide layer (2) 16B is an undoped GaN layer (thickness: 180 nm).

[0029] The p-side guide layer 16 is an undoped layer in consideration of light absorption by a dopant (Mg: magnesium, etc.), but may be doped to obtain good electrical conductivity. In addition, the In composition and layer thickness of the p-side guide layer (1) 16A can be appropriately selected to adjust the electric field distribution in the oscillation operation mode.

[0030] The electron barrier layer (EBL) 17 is Al 0.2 Ga 0.8 The p-cladding layer 18 is an Mg-doped p-Al 0.06 Ga 0.94 The p-contact layer 19 is an N layer (thickness: 290 nm). The p-contact layer 19 is an Mg-doped p-GaN layer (thickness: 25 nm).

[0031] In this specification, "n-side" and "p-side" do not necessarily mean n-type and p-type. For example, an n-side guide layer means a guide layer provided on the n-side of the active layer, and may be an undoped layer (or i-layer).

[0032] Furthermore, the n-clad layer 13 may be composed of multiple layers rather than a single layer, and in that case, all layers do not need to be n layers (n-doped layers) and may include an undoped layer (i layer). The same applies to the guide layer 16 and the p-clad layer 18. Furthermore, it is not necessary to provide all of the semiconductor layers described above, as long as there is a configuration having an n-type semiconductor layer, a p-type semiconductor layer, and an active layer (light-emitting layer) sandwiched between these layers.

[0033] An optical interference layer 31 is provided on the semiconductor structure layer 11, i.e., on (the upper surface of) the p-contact layer 19, and an optical reflection layer 32 is provided on the optical interference layer 31. Furthermore, a p-electrode (anode) 20B is provided on the optical reflection layer 32. The region where the optical interference layer 31 and the optical reflection layer 32 are formed is referred to as an anode region RA.

[0034] The side surfaces and the edge portions of the upper surface of the semiconductor structure layer 11 are covered with an insulating film 21 such as SiO2. The insulating film 21 is formed so as to cover the side surfaces of the optical interference layer 31, the optical reflection layer 32, and the p-electrode 20B, as well as the edge portions of the upper surface of the p-electrode 20B.

[0035] The light emitted from the active layer 15 is diffracted by the air hole layer (PC layer) 14P. The light diffracted by the air hole layer 14P and directly emitted from the air hole layer 14P (direct diffracted light Ld: first diffracted light) and the light diffracted by the air hole layer 14P and reflected by the light reflecting layer 32 (reflected diffracted light Lr: second diffracted light) are emitted to the outside from a light emitting region 20L (FIG. 2C) on the back surface (emission surface) 12R of the substrate 12.

[0036] 1B is an enlarged cross-sectional view schematically illustrating details of the air hole layer 14P (photonic crystal layer) of FIG. 1A and the air holes arranged in the air hole layer 14P. In this embodiment, the air hole layer 14P has air hole pairs 14K, each consisting of a main air hole 14K1 and a sub-air hole 14K2, two-dimensionally arranged at square lattice points. That is, the air hole layer 14P is formed as an air hole layer with a double lattice structure.

[0037] The present invention can be applied to a single lattice structure (single hole) in which one hole is provided at a lattice point, and to a hole layer generally having a multi-lattice structure. Therefore, in the following description, the hole pair 14K will be simply referred to as the hole 14K.

[0038] More specifically, the vacancies 14K are formed in a crystal growth surface (semiconductor layer growth surface), i.e., a plane parallel to the n-side guide layer 14, with a period PC, for example, in a square lattice pattern, and the vacancies 14K are two-dimensionally arranged at the square lattice point positions and embedded in the n-side guide layer 14.

[0039] FIG. 2A is a plan view schematically showing the top surface of the PCSEL device 10, FIG. 2B is a cross-sectional view schematically showing the cross section of the hole layer 14P in a plane parallel to the n-side guide layer 14, and FIG. 2C is a plan view schematically showing the bottom surface of the PCSEL device 10.

[0040] 2B, in the hole layer 14P, the holes 14K are periodically arranged in, for example, a rectangular hole-forming region 14R. As shown in FIG. 2C, the anode region RA (the region where the light interference layer 31 and the light reflection layer 32 are formed) is formed so as to be included in the hole-forming region 14R.

[0041] The inner diameter of the n-electrode 20A may be equal to or larger than the anode region RA when viewed from a direction perpendicular to the hole layer 14P.

[0042] The region inside n-electrode 20A is light emitting region 20L. Also, it is electrically connected to n-electrode 20A and is provided with bonding pad 20C for connecting a wire for power supply from the outside. (b) Optical interference layer, optical reflection layer, and interference of diffracted light 3 is a diagram showing the optical interference layer 31, the optical reflection layer 32, and the interference of diffracted light in the PCSEL device 10 of the first embodiment. More specifically, the upper part of Fig. 3 shows cross sections of the semiconductor structure layer 11, the optical interference layer 31, and the optical reflection layer 32, the middle part shows the intensity of the interference light LS generated by interference, and the lower part shows the beam shape and intensity of the interference light LS.

[0043] The optical interference layer 31 is formed of a light-transmitting conductor layer, such as indium tin oxide (ITO). The optical interference layer 31 is in ohmic contact with the p-contact layer 19. Note that the optical interference layer 31 is not limited to ITO, and a light-transmitting conductor such as zinc tin oxide (ZTO) can also be used.

[0044] The optical interference layer 31 has a circular shape when viewed from above, i.e., from a direction perpendicular to the semiconductor structure layer 11 (z direction). Specifically, the optical interference layer 31 is composed of an optical interference layer 31(1) in a central region R1 (hereinafter also referred to as a first region) that is circular and has a layer thickness d1, and an optical interference layer 31(2) in a peripheral region R2 (hereinafter also referred to as a second region) that is an outer region of the central region R1, has a ring shape concentric with the central region R1, and has a layer thickness d2 smaller than that of the central region R1 (d1>d2). The optical interference layer 31(1) and the optical interference layer 31(2) are also referred to as a first region layer and a second region layer, respectively.

[0045] In this embodiment, the diameter of the central region R1 is 100 μm, and the diameter (outer diameter) of the peripheral region R2 is 300 μm (i.e., the inner diameter is 100 μm). However, the diameters of the central region R1 and the peripheral region R2 can be set appropriately from the viewpoint of beam (transverse mode) control.

[0046] A metal layer is formed on the optical interference layer 31 as the optical reflection layer 32. Note that the p-electrode 20B provided on the optical reflection layer 32 is not shown in FIG.

[0047] The light reflecting layer 32 reflects the diffracted light from the hole layer 14 P. The light reflecting layer 32 is formed so as to cover the entire surface of the light interference layer 31 .

[0048] The light reflecting layer 32 may be made of, for example, highly reflective silver (Ag) with a reflectance of 85% or palladium (Pd) with a reflectance of 45%. The thickness of the light reflecting layer 32 is, for example, 200 nm, but is not limited to this.

[0049] The p-electrode 20B provided on the light-reflecting layer 32 (see FIG. 1A) is made of, for example, Ti / Pt / Au, but is not limited to this. For the p-electrode 20B, for example, Ti / Au, Ti / Al / Ti / Pt / Au, Ni / Pt / Au, etc. may be used. The thickness of the p-electrode 20B may be increased to serve as a pad electrode.

[0050] For clarity, the semiconductor layers of the semiconductor structure layer 11 are not shown except for the hole layer 14P and the active layer 15. The distance between the diffraction plane WS of the hole layer 14P and the interface between the semiconductor structure layer 11 and the optical interference layer 31 is d.

[0051] The interference of diffracted light in the PCSEL device 10 of this embodiment will be described below. Light emitted from the active layer 15 is diffracted by the hole layer 14P. Of the diffracted light, light that passes through the light interference layer 31(1) in the central region R1 and is reflected by the light reflecting layer 32 (reflected diffracted light Lr) interferes with the directly diffracted light Ld from the hole layer 14P to generate interference light (synthetic light) LS1 (interference light of the first region).

[0052] Similarly, in the peripheral region R2, the reflected diffracted light Lr that has passed through the optical interference layer 31(2) in the peripheral region R2 interferes with the direct diffracted light Ld from the hole layer 14P to generate interference light LS2 (interference light in the second region).

[0053] The layer thickness d1 of the optical interference layer 31(1) in the central region R1 is determined such that the direct diffracted light Lr and the reflected diffracted light Lr cancel each other out. Also, the layer thickness d2 of the optical interference layer 31(2) in the peripheral region R2 is determined such that the direct diffracted light Lr and the reflected diffracted light Lr reinforce each other.

[0054] Therefore, the intensities of the interference lights LS1 and LS2 generated and emitted in the central region (first region) R1 and the peripheral region (second region) R2 satisfy LS1 < LS2. That is, the peripheral region R2 is a brighter region than the central region R1.

[0055] For clarity of explanation and ease of understanding, the intensities of the interference lights LS1 and LS2 will be described as the interference light intensity LS1 and the interference light intensity LS2 using the same symbols, respectively. Also, when the interference lights LS1 and LS2 are not distinguished, they are collectively referred to as the interference light LS.

[0056] 2. Slope efficiency of the PCSEL device (a) Slope efficiency of the PCSEL device considering reflection from the reflecting surface As shown in FIG. 3, when the hole layer (photonic crystal layer) 14P is on the xy plane, the light propagating through the hole layer 14P forms a standing wave in the xy plane, and a part of it is diffracted by the photonic crystal in the z-axis direction orthogonal to the xy plane and emitted as laser light.

[0057] The reflecting surfaces SR1 and SR2 of the light reflecting layer 32 in the central region R1 and the peripheral region R2 (hereinafter, referred to as the reflecting surface SR when not particularly distinguished) are on a plane parallel to the hole layer 14P, and the laser light diffracted by the hole layer 14P and the reflecting surface SR are orthogonal.

[0058] In the PCSEL device 10, it is necessary to consider absorption at the reflecting surface SR and interference between the incident light and the reflected light in terms of the emission efficiency.

[0059] The cavity loss in the PCSEL device 10 can be divided into a loss component αp in the same plane as the hole layer 14P (xy plane) and a loss component αv in the perpendicular direction (z direction) that is orthogonal to the loss component αp. Of these, it is the perpendicular component αv that contributes to laser emission, but if a reflective surface SR is present, the emission efficiency must be considered taking into account absorption and reflection at the reflective surface SR.

[0060] In this specification, the loss in the in-plane direction αp, the loss in the perpendicular direction αv, and the slope efficiency ηSE are also expressed as follows:

[0061]

number

[0062] The component emitted in the vertical direction due to diffraction is αv, so if diffraction occurs evenly above and below the z axis (±z direction), the energy emitted in the ±z direction will be equal, and the laser light emitted in the ±z direction will be 0.5αv.

[0063] If the reflectivity of the reflecting surface SR is R, then of the laser light emitted in the direction of the reflecting surface SR (+z direction), the component absorbed by SR is 0.5αv(1-R), and the component reflected is 0.5αvR. If the phase difference between the light emitted from the holey layer 14P in the direction of the output surface 12R and the light reflected by the reflecting surface SR in the direction of the output surface 12R is θ, then the effective radiation coefficient αv1 emitted from the output surface is expressed by the following equation (1.1).

[0064]

number

[0065] Furthermore, the loss absorbed at the reflecting surface SR is 0.5αv(1-R), and the radiation loss α is expressed by the following equation (1.2).

[0066]

number

[0067] Therefore, the slope efficiency η SE (output efficiency) when the reflecting surface SR of the PCSEL device 10 is taken into consideration is expressed by the following formula (1.3).

[0068]

number

[0069] In the above equation, ηi is the injection efficiency during laser oscillation. In addition to the cavity loss, the above equation also takes into account the internal loss αi due to material absorption.

[0070] When the internal loss αi=0, equation (1.3) can be expressed as equation (1.4).

[0071]

number

[0072] That is, the larger αv / αp, the higher the slope efficiency ηSE. In the ideal case of ηi =1, R=1, θ=0, and αi=0, the slope efficiency ηSE versus αv / αp is shown in FIG.

[0073] 4, the slope efficiency η SE is saturated when αv / αp is equal to or greater than about 20. Therefore, from the viewpoint of increasing the slope efficiency η SE , it is preferable that αv be about 20 times αp.

[0074] Figure 5 shows the dependence of the slope efficiency η on the phase difference θ when αv / αp=20 and ITO / Ag (reflectivity R=0.85) and ITO / Pd (reflectivity R=0.45) are used as the reflective electrodes. Note that the slope efficiency η is normalized by the slope efficiency without reflection.

[0075] The dependence of the slope efficiency of a vertical cavity laser (VC-LD) without a photonic crystal layer on the phase difference θ is also shown.

[0076] In a vertical cavity laser (VC-LD), the slope efficiency varies along a cosine curve with respect to the phase difference θ. In other words, regions of relatively strong radiation intensity (hereinafter referred to as constructive regions) and regions of relatively weak radiation intensity appear periodically at intervals of 2π.

[0077] On the other hand, in a PCSEL element that resonates in the horizontal direction (in-plane direction of the air hole layer), the element region where the direct diffracted light Ld and the reflected diffracted light Lr relatively constructively interact (hereinafter referred to as the constructive region) and the element region where they relatively destructively interact (hereinafter referred to as the destructive region) in the vertical direction of the air hole layer exhibit characteristics that are different from other light-emitting devices such as vertical cavity lasers. This is because the total loss involved in oscillation (αtotal) is the sum of αv (loss due to emission), αi (loss due to components), and αp (loss related to resonance) (αtotal = αv + αi + αp), but αv and αi are involved in the interference of light emitted in the vertical direction.

[0078] As shown in FIG. 5, in the PCSEL element, the range of phase difference θ in the constructive region is wide, and the range of phase difference θ in the destructive region is narrow.

[0079] In other words, the thickness tolerance of the interference layer in the constructive interference region is wide, making it easy to control the film thickness and the output intensity. Furthermore, the range of the phase difference θ between the constructive and destructive interference regions of a PCSEL element varies depending on the reflectivity of the reflective layer.

[0080] Therefore, in a PCSEL device, although the tolerance for the thickness range of the interference layer in the weakening region is narrow, by reducing the reflectivity of the reflective layer located in the weakening region, the tolerance for the thickness range of the weakening region can be widened, making it easier to control the output intensity, just as with the constructive region.

[0081] (b) Wave source (diffraction plane) position The profile of the radiation wave emitted in the direction perpendicular to the hole layer 14P in the PCSEL device 10 of the first embodiment was calculated.

[0082] More specifically, for example, from Non-Patent Document 1, the coupled wave theory can be used to calculate the light propagating in the xy directions (in-plane directions) of the air hole layer 14P, the wave source (diffraction plane) of the diffracted wave by the air hole layer 14P, and the diffracted radiation wave emitted in the vertical direction.

[0083] FIG. 6 is a diagram showing the calculation results of the electric field amplitude of radiation waves that are radiated in the vertical direction (±z direction) when light propagating in the x-axis direction within the air hole layer 14P is diffracted by the air hole layer 14P.

[0084] In this calculation, the vacancy filling factor FF was set to 10%. It is known that in nitride materials, when vacancies are embedded in a layer grown on a +C-plane substrate, the vacancies have m-plane hexagonal columnar structures due to mass transport that occurs during the embedding growth (see, for example, Patent Document 1). Therefore, in this calculation, the vacancies 14K in the vacancy layer 14P were assumed to have hexagonal columnar structures with central axes extending in the z-axis direction. The vacancy period PC was set to 176 nm.

[0085] As shown in FIG. 6, the light diffracted by the hole layer 14P is emitted as radiation light symmetrically in the +z-axis direction and the −z-axis direction from a certain point (a point on the z-axis) in the hole layer 14P.

[0086] This origin (z=z) in the pore layer 14P ws ), this point is the diffraction plane (wave source) WS of the device. ws A surface that satisfies the above requirement and is parallel to the hole layer 14P is a diffraction surface, which functions as a wave source. For ease of understanding and simplicity of explanation, the same reference numerals will be used below, and such a surface will be referred to as the diffraction surface WS. In other words, the diffraction surface WS is the central plane of symmetry of the electric field amplitude when light standing in the hole layer 14P is diffracted symmetrically in a direction perpendicular to the hole layer 14P.

[0087] Since the electric field profile of the fundamental mode changes depending on the lattice structure (single lattice structure, multiple lattice structure) of the air hole layer, the position of the diffraction plane WS changes depending on the lattice structure of the air hole layer.

[0088] (c) Derivation of the layer thickness of the optical interference layer 31 First, if the average refractive index of the materials constituting the area from the diffractive surface (wave source) WS to the reflecting surface SR for the wavelength λ of the emitted light is denoted by nave, the distance dr between the diffractive surface WS and the reflecting surface SR can be expressed by the following equation (2.1):

[0089]

number

[0090] Note that equation (2.1) is derived from equation (2.2) below.

[0091]

number

[0092] The film thickness of the optical interference layer 31 can be calculated by subtracting the distance d between the diffractive surface WS and the optical interference layer 31 from the separation distance dr derived from equation (2.2).

[0093] Furthermore, from equation (1.4), the slope efficiency ηSE(0) when there is no reflection from a reflecting surface is given by the following equation (2.3).

[0094]

number

[0095] Therefore, in order for the slope efficiency ηSE(R) when there is reflection to be higher than when there is no reflection, it is sufficient to satisfy ηSE(R)>ηSE(0), and the phase difference θ that satisfies this condition is given by the following equation (2.4).

[0096]

number

[0097] Furthermore, the phase difference θ that satisfies ηSE(R)<ηSE(0) is given by the following equation (2.5).

[0098]

number

[0099] 7 is a diagram showing the relationship between the slope efficiency ηSE and the interference layer thickness with respect to the phase difference θ. The phase difference θ range WI indicates the range in which the direct diffracted light Ld and the reflected diffracted light Lr destructively interact, i.e., the range in which the normalized slope efficiency is less than 1. The phase difference range outside the phase difference range WI is the constructive range. For the constructive range, it is more preferable that the slope efficiency exceeds 1. The interference layer thickness (shown by the dashed line) was calculated by subtracting the distance d from the separation distance dr.

[0100] When the optical interference layer 31 and the optical reflection layer 32 are ITO / Ag (reflectivity R=0.85) and αv / αp=20, the ranges of destructive interaction and constructive interaction are given by the following formula (2.6) from the dependence of the slope efficiency ηSE and the thickness of the interference layer on the phase difference (θ) shown in FIG. 7. Destructive range: -208.4°<θ<-151.6° or 151.6°<θ<208.4° Constructive range: -360°≦θ≦-208.4° or -151.6°≦θ≦151.6°, Or, 208.4°≦θ≦360° (2.6) The distance dr from the wave source WS to the reflecting surface SR when the phase difference θ is within the above range is calculated. Since the phase of the emitted light Lr when it travels back and forth through dr should be as described above, the distance dr satisfies the following formula.

[0101] That is, the destructive condition is expressed by the following equation (2.7).

[0102]

number

[0103] Also, the strengthening condition is expressed by the following formula (2.8).

[0104]

Number

[0105] When the separation distance dr of formula (2.1) is calculated within the range of the phase difference θ of each digit of formula (2.6) and the distance d between the diffraction surface WS and the optical interference layer 31 is subtracted, the layer thickness d1 of the weakening region (central region R1) and the layer thickness d2 of the strengthening region (peripheral region R2) shown in the following formula (2.9) are obtained. Note that the calculation was performed with d = 1060 nm, λ = 435 nm, nave = 2.4, and m = 13. · d1: 110.9 nm < d1 < 125.2 nm, or 201.6 nm < d1 < 215.8 nm · d2: 72.8 nm ≤ d2 ≤ 110.9 nm, or 125.2 nm ≤ d2 ≤ 201.6 nm, or 215.8 nm ≤ d2 ≤ 254 nm ···(2.9) By determining the layer thickness d1 of the central region R1 and the layer thickness d2 of the peripheral region R2 so as to satisfy formula (2.9), the peripheral region R2 can be made brighter than the central region R1 (interference light intensity: LS1 < LS2), and beam control can be performed.

[0106] As schematically shown in FIG. 3, it is preferable that the layer thickness d2 of the strengthening region (peripheral region R2) is smaller than the layer thickness d1 of the weakening region (central region R1). This is because a laser beam with a desired beam shape can be obtained while suppressing the reduction in the emission intensity due to the material loss of the optical interference layer 31(2) in the strengthening region.

[0107] Therefore, it is more preferable to adopt the minimum value of 110.9 nm in formula (2.9) as the thickness d1 of the destructive region (central region R1) and the minimum value of 72.8 nm in formula (2.9) as the thickness d2 of the constructive region (peripheral region R2). In this case, the optical interference layer 31 has a convex structure in which the central region R1 is thicker than the peripheral region R2.

[0108] As described above, according to this embodiment, it is possible to provide a photonic crystal surface-emitting laser that can easily and accurately control the beam shape and has excellent beam (transverse mode) stability up to high output.

[0109] (d) Modification example 8 is a schematic cross-sectional view showing a modified example of the first embodiment. In this modified PCSEL device 40, the layer thickness d2 of the constructive region (peripheral region R2) is greater than the layer thickness d1 of the destructive region (central region R1).

[0110] That is, the optical interference layer 31 has a concave structure in which the peripheral region R2 is thicker than the central region R1. Even in this case, the beam shape can be controlled with high precision, and a photonic crystal surface-emitting laser with excellent beam (transverse mode) stability up to high output can be realized.

[0111] [Second embodiment] 9 is a diagram schematically illustrating the cross section, interference light intensity, and beam shape of a PCSEL device 50 of the second embodiment. In this embodiment, a light-reflecting layer 32(1) is formed on a light-interference layer 31(1), and a light-reflecting layer 32(2) with a reflectance different from that of the light-reflecting layer 32(1) is formed on a light-interference layer 31(2). In other respects, the PCSEL device 50 is similar to the PCSEL device 10 of the first embodiment.

[0112] More specifically, the optical interference layers 31(1) and 31(2) are ITO layers, the optical reflection layer 32(1) is Pd (reflectance R=0.45), and the optical reflection layer 32(2) is an Ag layer (reflectance R=0.85).

[0113] Similar to the PCSEL element 10 of the first embodiment, the central region R1 is a weakening region and the peripheral region R2 is a strengthening region. Therefore, the intensities of the interference light LS1 and the interference light LS2 in the central region R1 and the peripheral region R2 are such that LS1 < LS2. That is, the light reflection layer 32(1) with a relatively low reflectivity is applied to the region where the intensity of the interference light relatively weakens, and the light reflection layer 32(2) with a relatively high reflectivity is applied to the region where the intensity of the interference light relatively strengthens.

[0114] Fig. 10 shows the phase difference (θ) dependence of the interference layer thickness for the central region R1 where the light reflection layer 32(1) is Pd (reflectivity R = 0.45).

[0115] When the light reflection layer 32(1) is used, the weakening range and the strengthening range are obtained as in the following formula (2.10). · Weakening range: -230.2° < θ < -129.8° or 129.8° < θ < 230.2° · Strengthening range: -360° ≤ θ ≤ -230.2° or -129.8° ≤ θ ≤ 129.8° Or 230.2° ≤ θ ≤ 360° ···(2.10)

[0116] The layer thickness d1 of the weakening region (central region R1) is obtained by calculating the separation distance dr of formula (2.1) within the range of each phase difference θ of formula (2.10) and subtracting the distance d between the diffraction surface WS and the optical interference layer 31. The calculation was performed with d = 1060 nm, λ = 435 nm, nave = 2.4, and m = 13. · d1: 105.4 nm < d1 < 130.7 nm or 196.1 nm < d1 < 221.3 nm ···(2.11)

[0117] Here, since the light reflection layer 32(2) which is an Ag layer is applied to the strengthening region (peripheral region R2) in the second embodiment, the film thickness d2 is obtained in the same manner as formula (2.9).

[0118] By determining the layer thickness d1 of the central region R1 so as to satisfy Equation (2.11) and determining the layer thickness d2 of the peripheral region R2 so as to satisfy Equation (2.9), the peripheral region R2 can be made brighter than the central region R1 (interference light intensity: LS1 < LS2), and beam control can be performed.

[0119] Note that, as schematically shown in FIG. 9, it is preferable that the layer thickness d2 of the constructive interference region (peripheral region R2) is smaller than the layer thickness d1 of the destructive interference region (central region R1). This is because a laser beam with a desired beam shape can be obtained while suppressing a reduction in the emission intensity due to the material loss of the optical interference layer 31(2) in the constructive interference region.

[0120] In this embodiment as well, it is more preferable to adopt the minimum value 104.8 nm of Equation (2.11) as the layer thickness d1 of the destructive interference region (central region R1) and the minimum value 72.8 nm of Equation (2.11) as the layer thickness d2 of the constructive interference region (peripheral region R2).

[0121] As described above, according to this embodiment, the beam shape can be easily and highly accurately controlled, and a photonic crystal surface emitting laser excellent in beam (transverse mode) stability up to a high output can be provided.

[0122] [Third Embodiment] The PCSEL element of the third embodiment will be described below. In this embodiment, the optical interference layer 31 is divided into a first region R1, a second region R2, ···, an nth region Rn (n is an integer of 3 or more) in order from the center.

[0123] That is, the optical interference layer 31 has optical interference layers 31(1), 31(2), ···, 31(n). The optical interference layer 31(1) is provided in the first region R1 which is the central region, and the optical interference layers 31(1), 31(2), ···, 31(n) are provided in the peripheral region in order outside it.

[0124] 11 is a diagram schematically illustrating the cross section, interference light intensity, and beam shape of a PCSEL device 60 according to the third embodiment. In the PCSEL device 60, the optical interference layer 31 is divided into a first region R1, a second region R2, and a third region R3 (n=3) in that order from the center.

[0125] That is, the light interference layer 31 is made up of, from the center, a light interference layer 31(1), a light interference layer 31(2), and a light interference layer 31(3). On the light interference layer 31, a light reflecting layer 32 is provided.

[0126] More specifically, the diameters of the first region R1, the second region R2, and the third region R3 are 100 μm, 200 μm, and 300 μm, respectively.

[0127] The interference light intensity LS1 of the first region R1 (central region) is the greatest, the interference light intensity LS2 of the second region R2 is the smallest, and the interference light intensity LS3 of the third region R3 has an intensity intermediate between that of the first region R1 and that of the second region R2.

[0128] That is, the thicknesses of the optical interference layers 31(1), 31(2), and 31(3) are determined so that LS1>LS3>LS2 holds. The thickness of each optical interference layer can be determined based on the phase difference (θ) dependency of the interference layer thickness described in the first and second embodiments.

[0129] Specifically, the thicknesses of the ITO layers of the light interference layer 31(1), the light interference layer 31(2), and the light interference layer 31(3) are 73 nm, 118 nm, and 103 nm, respectively.

[0130] According to this embodiment, the beam shape can be easily and precisely controlled, and a photonic crystal surface-emitting laser with excellent beam (transverse mode) stability up to high output can be provided, similar to the above-described embodiments.

[0131] In particular, according to this embodiment, the second region R2, which has a lower interference light intensity than the first region R1 and the third region R3, which are regions with high interference light intensity, is provided between these regions. In other words, the regions R1 and R3, which have high interference light intensity, can be provided at a distance from each other.

[0132] Therefore, for example, when heating an object with a light beam, it is possible to adjust the heating position and heating process. For example, when welding by moving the irradiation position of the light beam, the workpiece can be preheated by the light of region R3, which is irradiated first in the traveling direction of the light beam, followed by the main processing by the light of region R1, and then the post-processing annealing by the light of region R3. This has the advantage of improving the quality of the welding and allowing the post-processing to be performed all at once.

[0133] Although the case where the optical interference layer 31 is made up of three regions has been described, the same can be applied to a case where the optical interference layer 31 is generally made up of a first region R1, a second region R2, . . . , an nth region Rn.

[0134] In this case, the interference light intensity of each region can be determined based on the phase difference (θ) dependency of the interference layer thickness so as to obtain a desired beam shape. That is, the interference light intensity LSj of the jth region Rj (j=1, 2, . . . , n) can be determined to be the desired intensity. Also, as in the second embodiment, light reflecting layers 32(1) and 32(2) having different reflectivities may be used.

[0135] In the above, the embodiments of the present invention have been described in detail. In the above embodiments, the case where the optical interference layer has a circular shape has been described, but in the present invention, the term "circular shape" includes an elliptical shape and an oval shape, and the term "annular shape" includes an elliptical ring shape and an oval ring shape.

[0136] Furthermore, the shape of the light interference layer is not limited to a circular shape, and it may be a rectangular shape, a polygonal shape, etc. Furthermore, it is preferable that each region of the light interference layer has a similar shape that is concentric.

[0137] The dielectrics, reflective metals, and their compositions and numerical values ​​in the above embodiments are merely examples and may be modified as appropriate within the scope of the present invention. Furthermore, while single-grating and double-grating PCSEL devices have been described as examples, the present invention is generally applicable to multi-grating PCSEL devices.

[0138] Furthermore, although the present invention has been described with reference to a porous layer in which the pores have a hexagonal columnar shape, the present invention can also be applied to cases in which the pores have an irregular columnar shape such as a cylindrical, rectangular, polygonal, or teardrop shape.

[0139] As described above in detail, according to the present embodiment, the beam shape can be easily and precisely controlled, and a photonic crystal surface-emitting laser with excellent beam (transverse mode) stability up to high output can be provided. [Explanation of symbols]

[0140] 10, 40, 50, 60: PCSEL element, 12: substrate, 14: n-side guide layer (first guide layer), 14K: hole / hole pair, 14P: photonic crystal layer (hole layer), 15: active layer (ACT), 16: p-side guide layer (second guide layer), 20A: n-electrode, 20B: p-electrode, 31, 31(1), 31(2): optical interference layer (transparent conductor layer), 32, 32(1), 32(2): optical reflection layer, d: distance between diffraction surface WS and optical interference layer 31, dr: separation distance, Ld: direct diffracted light, Lr: reflected diffracted light, R1: central region (first region), R2: peripheral region (second region), SR, SR1, SR2: reflecting surface, WS: diffraction surface (wave source)

Claims

1. a light-transmitting substrate; an n-type semiconductor layer provided on the substrate; an active layer provided on the n-type semiconductor layer; a p-type semiconductor layer provided on the active layer; a hole layer that is a photonic crystal layer included in the n-type semiconductor layer and has holes that are arranged with two-dimensional periodicity in a plane parallel to the active layer; a light reflecting layer provided on the p-type semiconductor layer and having a reflecting surface; a transparent conductive layer provided between the reflective surface and the p-type semiconductor layer, a light emitting surface on the rear surface of the substrate; the hole layer has a diffraction surface that is a wave source when light standing in the hole layer is diffracted in a direction perpendicular to the hole layer, a weakening region in which a separation distance between the diffracting surface and the reflecting surface is set so that the light intensity of interference light generated by interference between a first diffracted light diffracted from the diffracting surface toward the light exit surface and a second diffracted light diffracted from the diffracting surface toward the light reflecting layer and reflected by the reflecting surface is smaller than the light intensity of the first diffracted light; a constructive region in which the diffracting surface and the reflecting surface are spaced apart from each other such that the light intensity of the interference light is greater than the light intensity of the first diffracted light; A surface-emitting laser element having the same.

2. the transparent conductive layer has, in order from the center, a first region layer, a second region layer, ..., a k-th region layer (k is an integer of 2 or more), the first region layer is provided in the weakening region, 2. The surface-emitting laser element according to claim 1, wherein the second region layer is provided in the constructive interaction region and has a layer thickness different from that of the first region layer.

3. 3. The surface-emitting laser element according to claim 2, wherein the second region layer has a thickness smaller than that of the first region layer.

4. 4. The surface-emitting laser element according to claim 2, wherein the light-reflecting layer on the first region layer and the light-reflecting layer on the second region layer have mutually different reflectivities.

5. the transparent conductive layer has at least a first region layer, a second region layer, and a third region layer; the first region layer and the third region layer of the transparent conductive layer are provided in the constructive interaction region, 2. The surface-emitting laser element according to claim 1, wherein the second region layer is provided in the mutually weakening region.

6. The phase difference between the first diffracted light diffracted by the diffracting surface and the second diffracted light diffracted by the diffracting surface and reflected by the reflecting surface is defined as θ (deg), the wavelength of the first diffracted light is defined as λ, and the average refractive index of the layer from the diffracting surface to the reflecting surface is defined as n ａｖｅ When m is an integer equal to or greater than 0, the separation distance is expressed by the following formula: The phase difference θ is expressed by the following formula: where R is the reflectance of the reflecting surface, αp and αv are the losses of the hole layer in the in-plane direction and the perpendicular direction to the hole layer, respectively, and αi is the internal loss. and the constructive region satisfies 6. The surface-emitting laser element according to claim 1, wherein the above formula (1) is satisfied.

7. The surface-emitting laser element according to claim 1 , wherein the transparent conductive layer has a circular shape.

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