Surface-emitting laser element and method for manufacturing a surface-emitting laser element

Abstract

The surface-emitting laser element has: a first guiding layer having a photonic crystal layer and an embedding layer, the photonic crystal layer being formed on the c-plane of a Group-III nitride semiconductor and having air holes two-dimensionally periodically arranged in a plane parallel to the layer, the embedding layer being formed on the photonic crystal layer and closing the air holes; an active layer formed on the first guiding layer; and a second guiding layer formed on the active layer, an air hole group being arranged at each square lattice point in a plane parallel to the photonic crystal layer, the air hole group including at least a main air hole and a sub-air hole having a size smaller than that of the main air hole, the main air hole having a regular hexagonal prism shape, a flat hexagonal prism shape or an elliptical cylinder shape with a major axis parallel to the <11-20> axis.

Description

Technical Field

[0001] The present invention relates to a surface-emitting laser element and a method for manufacturing the same, and more particularly to a photonic crystal surface-emitting laser element and a method for manufacturing the same. Background Art

[0002] In recent years, the development of a photonic-crystal surface-emitting laser using a photonic crystal (PC: Photonic-Crystal) has been promoted.

[0003] For example, Patent Document 1 describes a two-dimensional photonic-crystal surface-emitting laser light source having a two-dimensional photonic crystal in which a plurality of aggregate bodies of refractive-index different regions are periodically arranged in a plate-shaped base material, the aggregate bodies of refractive-index different regions being composed of a plurality of regions having refractive indices different from those of the base material and at least two of the regions having different thicknesses from each other. And the following is disclosed: Compared with a two-dimensional photonic crystal in which cylindrical refractive-index different regions are periodically arranged, by this configuration, it is possible to reduce the symmetry in the plane parallel to the base material and suppress a decrease in the extraction efficiency of laser light caused by the cancellation of the antisymmetric mode due to interference.

[0004] When an embedded layer embedding the photonic crystal is grown on a two-dimensional photonic crystal in which a plurality of such air holes are periodically arranged in a crystal plane, there is the following problem: the surface of the embedded layer becomes a rough surface, and the quality of the active layer grown on the embedded layer deteriorates.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 4294023 Gazette Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] As described above, in a photonic-crystal surface-emitting laser, there is the following problem: the surface of the embedded layer embedded in the two-dimensional photonic crystal layer is rough, and the quality of the active layer formed on the embedded layer deteriorates.

[0010] In addition, the inventors of the present application obtained the following insight: when a two-dimensional photonic crystal in which a group of air holes having different sizes are periodically arranged is embedded using an embedded layer, the surface of the embedded layer is rougher than in the case of a two-dimensional photonic crystal composed of air holes of a single size.

[0011] In particular, the following insight was obtained: in the process of forming the embedding layer, the shape of the air holes changes due to mass transfer, and due to this change in the shape of the air holes, the shape changes of adjacent air holes interfere with each other, resulting in unevenness on the surface of the embedding layer.

[0012] The present invention was completed in view of the above problems, and an object thereof is to provide a photonic crystal surface emitting laser and a method for manufacturing the same, the photonic crystal surface emitting laser having a two-dimensional photonic crystal (hereinafter, also referred to as a multi-lattice photonic crystal) formed by arranging a plurality of air holes of different sizes at lattice points and periodically arranging groups of the plurality of air holes, and the flatness of the surface of the embedding layer embedding the multi-lattice photonic crystal is greatly improved.

[0013] Another object of the present invention is to provide a photonic crystal surface emitting laser and a method for manufacturing the same, the photonic crystal surface emitting laser having high flatness and crystallinity of an active layer formed on a multi-lattice photonic crystal layer, high light extraction efficiency, and capable of oscillating with a low threshold current density and a high quantum efficiency.

[0014] Means for solving the problem

[0015] The surface emitting laser element according to the first embodiment of the present invention is composed of a group III nitride semiconductor and has:

[0016] A first guiding layer having a photonic crystal layer and an embedding layer, the photonic crystal layer being formed on the c-plane of the group III nitride semiconductor and having air holes two-dimensionally periodically arranged in a plane parallel to the layer, and the embedding layer being formed on the photonic crystal layer and closing the air holes;

[0017] An active layer formed on the first guiding layer; and

[0018] A second guiding layer formed on the active layer,

[0019] At each square lattice point in a plane parallel to the photonic crystal layer, a group of air holes is arranged, the group of air holes including at least a main air hole and a sub-air hole having a size smaller than that of the main air hole,

[0020] The main air hole has a regular hexagonal prism shape, a flat hexagonal prism shape or an elliptical cylinder shape with its major axis parallel to the <11-20> axis.

[0021] A method for manufacturing a surface emitting laser element according to another embodiment of the present invention is characterized by having: a step of forming a guiding layer on the c-plane of a group III nitride semiconductor;

[0022] A step of forming an etching mask on the guiding layer, the etching mask having an opening group including at least a main opening and a sub-opening having a size smaller than that of the main opening at each square lattice point;

[0023] A step of etching the guiding layer using the etching mask to form a main hole and a sub-hole;

[0024] A step of performing crystal growth including mass transfer to form an embedding layer that closes the openings of the main hole and the sub-hole, and forming a multi-lattice photonic crystal layer in which a group of air holes is arranged at each of the square lattice points, the group of air holes including a main air hole and a sub-air hole having a size smaller than that of the main air hole; and

[0025] A step of forming a semiconductor layer including an active layer on the multi-lattice photonic crystal layer,

[0026] The main air hole has a regular hexagonal prism shape, a flat hexagonal prism shape, or an elliptical cylinder shape with its major axis parallel to the <11-20> axis. Description of the Drawings

[0027] Figure 1A is a cross-sectional view schematically showing an example of the structure of a photonic crystal laser (PCSEL) 10.

[0028] Figure 1B is schematically showing Figure 1A an enlarged cross-sectional view of the photonic crystal layer 14P and the pair of air holes 14K arranged in the photonic crystal layer 14P in.

[0029] Figure 2A is a plan view schematically showing the upper surface of the photonic crystal laser 10.

[0030] Figure 2B is schematically showing a cross-sectional view of the cross-section of the photonic crystal layer 14P at a plane parallel to the n-guiding layer 14 ( Figure 1B , A-A cross-section).

[0031] Figure 2C is a plan view schematically showing the bottom surface of the photonic crystal laser 10.

[0032] Figure 3 is a top view schematically showing a resist in which an opening pair composed of an elliptical main opening K1 and a sub-opening K2 is two-dimensionally arranged in a square lattice pattern in a plane.

[0033] Figure 4 is an SEM image of the GaN surface on which the holes 14H1 and 14H2 are formed.

[0034] Figure 5 is an SEM image of the upper surface of the guiding layer showing the air hole shapes of the main air hole 14K1 and the sub-air hole 14K2 in this embodiment.

[0035] Figure 6A is showing Figure 5SEM image of the cross-section at line A-A.

[0036] Figure 6B shows Figure 5 SEM image of the cross-section at line B-B.

[0037] Figure 7 is an SEM image showing the cylindrical holes CH formed on the GaN surface portion in Comparative Example 1.

[0038] Figure 8A is a graph showing the I-L characteristics of the PCSEL element 10 of Example 1 and the PCSEL element of Comparative Example 1.

[0039] Figure 8B is a graph showing the emission spectra near the threshold current of the PCSEL element 10 of Example 1 and the PCSEL element of Comparative Example 1.

[0040] Figure 9A is an SEM image of the upper surfaces of the main hole 14H1 and the sub-hole 14H2 of the structure (Structure A) formed with the main hole and the sub-hole in the same manner as in Example 1.

[0041] Figure 9B is an SEM image of the upper surfaces of the main hole CH1 and the sub-hole CH2 of Comparative Example 2 (Structure B).

[0042] Figure 10A is an AFM image showing the surface morphology of the embedding layer after embedding the main air hole and the sub-air hole in the case of Structure A (Example 2).

[0043] Figure 10B is an AFM image showing the surface morphology of the embedding layer after embedding the main air hole and the sub-air hole in the case of Structure B (Comparative Example 2).

[0044] Figure 11A is a top view schematically showing the shape change of the holes during the formation of the embedding layer in the case of Structure A (Example 2).

[0045] Figure 11B is a top view schematically showing the shape change of the holes during the formation of the embedding layer in the case of Structure B (Comparative Example 2).

[0046] Figure 12A is a graph showing the vertical resonator loss α when the relative positions Δx, Δy (Δx = Δy) of the sub-air hole 14K2 with respect to the main air hole 14K1 in the structure of Example 1 are changed from 0.0 PC to 0.5 PC. n

[0047] Figure 12B ​It is a graph showing the resonator loss α in the horizontal direction when the relative positions Δx, Δy (Δx = Δy) of the secondary air hole 14K2 with respect to the primary air hole 14K1 in the structure of Example 1 are changed from 0.0 PC to 0.5 PC. p of the graph.

[0048] Figure 12C It is a graph showing the resonator loss α in the vertical direction n with respect to the total resonator loss (α p + α n ) that is, the ratio R n of the graph.

[0049] Figure 13 It is a diagram showing the photon band structure near the Γ point of the square lattice photonic crystal.

[0050] Figure 14 It is a graph showing the threshold gain (resonator loss) of each mode obtained by the coupled wave theory when Δx and Δy are changed in Example 1.

[0051] Figure 15 It is a diagram schematically showing the refractive index, carrier density, and photon density of the current injection region.

[0052] Figure 16A It is a diagram schematically showing the frequencies of the photon band edges near the current injection region in the case of the band edge modes A and B.

[0053] Figure 16B It is a diagram schematically showing the frequencies of the photon band edges near the current injection region in the case of the band edge modes C and D.

[0054] Figure 17A It is a diagram schematically showing the refractive index, carrier density, and photon density of the current injection region when oscillating in the band edge modes A and B. The cases with and without considering the photon band effect are shown by solid and dashed lines respectively.

[0055] Figure 17B Schematically shows the refractive index, carrier density, and photon density of the current injection region when oscillating in the band edge modes C and D. The cases with and without considering the photon band effect are shown by solid and dashed lines respectively.

[0056] Figure 18 It is an SEM image of the GaN surface on which the holes 14H1 and 14H2 are formed.

[0057] Figure 19A It is an SEM image of the upper surface of the guiding layer showing the hole shapes of the primary air hole 14K1 and the secondary air hole 14K2 in Example 3.

[0058] Figure 19B is a SEM image showing a cross-section along line A-A of Figure 19A .

[0059] Figure 19C is a SEM image showing a cross-section along line B-B of Figure 19A .

[0060] Figure 20A is a graph showing the I-L characteristics of the PCSEL element 10 of Example 3 and the PCSEL element of Comparative Example 1.

[0061] Figure 20B is a graph showing the emission spectra near the threshold current of the PCSEL element 10 of Example 3 and the PCSEL element of Comparative Example 1.

[0062] Figure 21A is a graph showing the resonator loss α in the vertical direction with respect to d (the relative position of the secondary air hole with respect to the main air hole) n .

[0063] Figure 21B is a graph showing the resonator loss α in the horizontal direction with respect to the relative position d p .

[0064] Figure 21C is a graph showing the correlation of R n with respect to the relative position d.

[0065] Figure 21D is a graph showing the threshold gain (resonator loss) of each mode obtained by the coupled-wave theory when Δx and Δy (relative position d) are changed in Example 3.

[0066] Figure 22A is a graph showing R n with respect to the air hole filling ratio FF1 / FF2.

[0067] Figure 22B is a graph showing the sum of the resonator losses in the vertical and horizontal directions (α n +α p ) with respect to the air hole filling ratio FF1 / FF2. DETAILED DESCRIPTION

[0068] Hereinafter, preferred embodiments of the present invention will be described, but they can be appropriately changed and combined. In the following description and drawings, substantially the same or equivalent parts are denoted by the same reference numerals.

[0069] [Structure of Photonic Crystal Surface Emitting Laser]

[0070] A photonic crystal surface emitting laser (hereinafter also referred to as a PCSEL) is an element that has a resonator layer in a direction parallel to a semiconductor light emitting structure layer (n-guiding layer, light emitting layer, p-guiding layer) constituting a light emitting element and emits coherent light in a direction orthogonal to the resonator layer.

[0071] On the other hand, a distributed Bragg reflector (DBR) laser having a pair of resonator mirrors (Bragg reflectors) sandwiching a semiconductor light emitting structure layer is known, and the photonic crystal surface emitting laser (PCSEL) differs from the DBR laser in the following aspects. That is, in the 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. That is, with respect to the resonance direction (in the plane parallel to the PC layer), the light extraction direction is the perpendicular direction.

[0072] Figure 1A FIG. is a cross-sectional view schematically showing an example of the structure (first PCSEL structure) of a photonic crystal laser element (PCSEL element) 10. As Figure 1A shown, a semiconductor structure layer 11 is formed on a substrate 12. In addition, the semiconductor structure layer 11 is composed of a hexagonal nitride semiconductor. The semiconductor structure layer 11 is, for example, composed of a GaN-based semiconductor.

[0073] More specifically, a semiconductor structure layer 11 is formed on the substrate 12, that is, an n-cladding layer (first cladding layer of the first conductivity type) 13, an n-guiding layer (first guiding layer) 14, an active layer 15, a p-guiding layer (second guiding layer) 16, an electron blocking layer (EBL: Electron Blocking Layer) 17, a p-cladding layer (second cladding layer of the second conductivity type) 18, and a p-contact layer 19 are sequentially formed. In addition, the case where the first conductivity type is n-type and the second conductivity type, which is the opposite conductivity type of the first conductivity type, is p-type is described, but the first conductivity type and the second conductivity type may also be p-type and n-type, respectively.

[0074] The n-guiding layer 14 is composed of a lower guiding layer 14A, a photonic crystal layer (air hole layer or PC layer) 14P, and an embedding layer 14B. In addition, the embedding layer 14B is composed of a first embedding layer 14B1 and a second embedding layer 14B2.

[0075] In addition, in this specification, "n-" and "p-" mean "n-side" and "p-side", and do not necessarily mean having n-type and p-type. For example, the n-guiding layer means a guiding layer provided on the n-side of the active layer, and may be an undoped layer (or i-layer).

[0076] In addition, the n-cladding layer 13 may not be a single layer but may be composed of multiple layers. In this case, it is not necessary for all layers to be n-layers (n-doped layers), and undoped layers (i-layers) may also be included. The same applies to the guiding layer 16 and the p-cladding layer 18.

[0077] In addition, the specific and detailed semiconductor layer structure of the photonic crystal laser element 10 has been described above, but only one example of the element structure is shown. In short, as long as it is configured to include a first semiconductor layer (or guiding layer) having a photonic crystal layer 14P, a second semiconductor layer (or guiding layer), and an active layer (light-emitting layer) sandwiched between these layers, and emits light by injecting current into the active layer.

[0078] For example, the photonic crystal laser element does not need to have all of the above semiconductor layers. Alternatively, the photonic crystal laser element may also have various semiconductor layers for improving element characteristics (such as a hole blocking layer, a light confinement layer, a current confinement layer, a tunnel junction layer, etc.).

[0079] In addition, an n-electrode (cathode) 20A is formed on the back surface of the substrate 12, and a p-electrode (anode) 20B is formed on the p-contact layer 19 (upper surface). The side surface of the semiconductor structure layer 11 and the upper side surface of the substrate 12 are covered with an insulating film 21 such as SiO2. In addition, the side surface of the p-electrode 20B and the surface of the p-contact layer 19 are covered with the insulating film 21 so as to cover the edge portion of the upper surface of the p-electrode 20B.

[0080] The light directly emitted from the photonic crystal layer (PC layer) 14P (direct emission light Ld) and the light emitted from the photonic crystal layer 14P and reflected by the p-electrode 20B (reflected emission light Lr) are emitted to the outside from the light emission region 20L on the back surface of the substrate 12.

[0081] Figure 1B is a schematic enlarged cross-sectional view showing Figure 1A the photonic crystal layer 14P and the air hole pair 14K arranged in the photonic crystal layer 14P in. The air hole pair 14K (main air hole 14K1 and sub-air hole 14K2) has a period PC in a square lattice shape, for example, in the crystal growth surface (semiconductor layer growth surface), that is, in a plane parallel to the n-guiding layer 14 (in the figure, the A-A cross-section). The air hole pairs 14K are two-dimensionally arranged at the square lattice point positions and embedded in the n-guiding layer 14 to form.

[0082] Figure 2A is a plan view schematically showing the upper surface of the photonic crystal laser (PCSEL) 10, Figure 2B is a schematic view showing the plane parallel to the n-guiding layer 14 of the photonic crystal layer (PC layer) 14P ( Figure 1B, sectional view of the cross-section at the A-A cross-section Figure 2C is a plan view schematically showing the bottom surface of the photonic crystal laser (PCSEL) 10.

[0083] As Figure 2B shown, in the photonic crystal layer 14P, pairs of air holes 14K are periodically arranged within an air hole formation region 14R having, for example, a rectangular shape. As Figure 2C shown, the n electrode (cathode) 20A is provided as an annular electrode outside the air hole formation region 14R so as not to overlap with the air hole formation region 14R when viewed from a direction perpendicular to the photonic crystal layer 14P. The region inside the n electrode 20A is the light emission region 20L. In addition, a bonding pad 20C is provided that is electrically connected to the n electrode 20A and connected to a wire for supplying power from the outside.

[0084] [Example 1]

[0085] 1. Manufacturing process of the photonic crystal laser (PCSEL) 10

[0086] Hereinafter, the manufacturing process of the PCSEL element 10 will be described in detail. As the crystal growth method, the MOVPE (Metalorganic Vapor Phase Epitaxy) method was used, and a semiconductor structure layer 11 was grown on the growth substrate 12 by atmospheric pressure (atmospheric pressure) growth. In addition, in the processes described below, Sn refers to step n.

[0087] In addition, the layer thickness, carrier concentration, group III (III group) and group V (V group) raw materials, temperature, etc. shown below are merely examples unless otherwise specified.

[0088] [S1: Substrate preparation process]

[0089] A GaN single crystal having a (0001) plane, i.e., a "+c" plane, on which Ga atoms are arranged on the outermost surface, is prepared as the main surface. The main surface can be either the front surface or, for example, a substrate offset by about 1° in the m-axis direction. For example, a substrate offset by about 1° in the m-axis direction can achieve mirror growth under a wide range of growth conditions.

[0090] The substrate surface (back surface) provided with the light emission region 20L opposite to the main surface is a (000-1) plane, i.e., a "-c" plane, on which N atoms are arranged on the outermost surface. The -c plane is resistant to oxidation and the like, and is therefore suitable as a light extraction surface.

[0091] In this embodiment, an n-type GaN single crystal is used as the GaN substrate 12. The n-type GaN substrate 12n has the function of a contact layer with the electrode.

[0092] [S2: n-cladding formation process]

[0093] On the +c-plane GaN substrate 12, an n-type AlGaN layer with an Al composition of 4% is grown to a thickness of 2 μm as the n-cladding layer 13. The AlGaN layer is grown by supplying trimethylgallium (TMG) and trimethylaluminum (TMA) as sources of group III atoms to the GaN substrate heated to 1100 °C. 0.04 Ga 0.96 N layer. Doping of carriers is performed by simultaneously supplying silane (SiH4) with the above raw materials (Si doping). The carrier concentration at room temperature at this time is about 4×10

[0094] cm 17 cm -3 .

[0095] [S3a: Process of forming lower guiding layer + air hole preparation layer]

[0096] Next, TMG is supplied, and an n-type GaN is grown to a thickness of 250 nm as a preparation layer for the n-guiding layer 14. Doping of carriers is performed by simultaneously supplying silane (SiH4) in the same manner as the AlGaN layer. The carrier concentration at this time is about 4×10 17 cm -3 .

[0097] This grown layer is a preparation layer for forming a layer composed of a lower guiding layer 14A and a photonic crystal layer 14P.

[0098] In addition, hereinafter, for the sake of convenience of explanation and easy understanding, the substrate 12 (substrate with grown layer) on which such a grown layer is formed is sometimes simply referred to as the substrate.

[0099] [S3b: Process of forming holes and air holes]

[0100] After forming the above preparation layer, the substrate is taken out from the chamber of the MOVPE apparatus, and fine holes are formed on the surface of the grown layer. More specifically, after obtaining a clean surface by cleaning the substrate, a silicon nitride film (Si x N y ) is formed by plasma CVD. An electron beam lithography resist is coated thereon by spin coating, and it is put into an electron beam (EB) lithography apparatus for patterning of a two-dimensional periodic structure.

[0101] As Figure 3 shown, the following patterning is performed: Pairs of openings composed of an elliptical main opening K1 and a sub-opening K2 smaller than the main opening K1 are two-dimensionally arranged in a square lattice pattern with a period PC = 164 nm in the plane of the resist. In addition, in order to make the drawings clear, the opening parts are shown by hatching.

[0102] More specifically, the center of gravity CD1 of the main opening K1 is arranged in a square lattice pattern with a period PC = 164 nm in two directions (x-direction and y-direction) that are orthogonal to each other. Similarly, for the sub-opening K2, the center of gravity CD2 thereof is arranged in a square lattice pattern with a period PC = 164 nm in the x-direction and the y-direction.

[0103] [The major axes of the main opening K1 and the sub-opening K2 are parallel to the <11-20> direction of the crystal orientation, and the minor axes of the main opening K1 and the sub-opening K2 are parallel to the <1-100> direction.

[0104] In addition, the center of gravity CD2 of the sub-opening K2 is spaced apart from the center of gravity CD1 of the main opening K1 by Δx and Δy. Here, let Δx = Δy. That is, the center of gravity CD2 of the sub-opening K2 is spaced apart from the center of gravity CD1 of the main opening K1 in the <1-100> direction. Specifically, the distance between the centers of gravity in the x-direction Δx and the distance between the centers of gravity in the y-direction Δy are 65.6 nm (= PC × 0.4).

[0105] In addition, the major diameter of the main opening K1 is 125 nm, the minor diameter is 50 nm, and the ratio of the major diameter to the minor diameter (major diameter / minor diameter) = 2.50. The major diameter of the sub-opening K2 is 57.5 nm, the minor diameter is 50 nm, and the major diameter / minor diameter = 1.15.

[0106] After developing the patterned resist, the Si x N y film is selectively dry-etched by an ICP-RIE (Inductive Coupled Plasma-Reactive Ion Etching) apparatus. Thus, the main opening K1 and the sub-opening K2 arranged in a square lattice pattern with a period of 164 nm are formed to penetrate the Si x N y film.

[0107] In addition, the period (pore spacing) PC is calculated as PC = λ / n = 164 nm by setting the oscillation wavelength (λ) to 410 nm and the refractive index (n) of GaN to 2.5.

[0108] Next, the resist is removed, and the patterned Si x N y film is used as a hard mask, and hole portions (holes) are formed on the GaN surface portion. By dry-etching GaN in the depth direction using a chlorine-based gas and argon in an ICP-RIE apparatus, elliptical columnar air holes (holes) 14H1 and 14H2 that are dug perpendicularly to the GaN surface are formed. In addition, in this process, in order to distinguish the holes dug in the GaN surface portion by this etching from the air holes in the photonic crystal layer 14P, they are hereinafter simply referred to as holes.

[0109] [S3c: Cleaning Process]

[0110] After degreasing and cleaning the substrate with holes 14H1 and 14H2 formed, Si is removed using buffered hydrofluoric acid (HF). x N y film. Figure 4 The SEM (Scanning Electron Microscope) image of the GaN surface at this time is shown.

[0111] As Figure 4 shown in the surface SEM image, multiple hole pairs 14H (main hole 14H1 and sub-hole 14H2) are formed in a two-dimensional square lattice arrangement with a period PC of 164 nm, that is, two-dimensionally arranged at the square lattice points. Holes 14H1 and 14H2 are substantially elliptical cylindrical hole parts or cavities that open on the upper surface (GaN surface).

[0112] More specifically, the major axis length LH1 of the opening of the main hole 14H1 in the GaN surface is 124 nm, the minor axis length WH1 is 50 nm (RH1 = major axis / minor axis = 2.49), and the major axis length LH2 of the opening of the sub-hole 14H2 is 57.1 nm, the minor axis length WH1 is 50.0 nm (RH2 = major axis / minor axis = 1.14).

[0113] At this time, the intervals between the center of gravity CD1 of the main hole 14H1 and the center of gravity CD2 of the sub-hole 14H2 in the x-direction and y-direction are 65.3 nm (= 0.4 × PC) respectively. The major axes of the main hole 14H1 and the sub-hole 14H2 are arranged parallel to the <11-20> axis (i.e., the a-axis).

[0114] In addition, as Figure 4 shown, the x-direction and y-direction are directions inclined 45° with respect to the major axis direction (<11-20> direction) and the minor axis direction (<1-100> direction) of the openings of the main hole 14H1 and the sub-hole 14H2 respectively. In this specification, the x-y coordinates are also referred to as the air hole coordinates.

[0115] [S3d: Embedded Layer Formation Process]

[0116] The substrate is re-introduced into the reactor of the MOVPE apparatus, ammonia (NH3) is supplied and the temperature is raised to 950 °C (the first embedding temperature), then trimethylgallium (TMG) and NH3 are supplied to seal the openings of the main hole 14H1 and the sub-hole 14H2, and the first embedded layer 14B1 is formed.

[0117] First, during the process of reaching the first temperature region (above 800 °C and below 1100 °C) (heating process), in the supplied NH3 atmosphere, mass transfer of Ga atoms on the surface of the growth substrate occurs, forming an eaves portion composed of {1-101} planes and {1-100} planes to enclose the opening of the hole formed on the n-cladding.

[0118] Secondly, through TMG supplied after reaching the first temperature region, the aforementioned eaves grow and merge in the direction of the hole center, so that the main hole 14H1 and the sub-hole 14H2 are closed and embedded. Thus, the first embedded layer 14B1 is formed.

[0119] Next, after closing the main hole 14H1 and the sub-hole 14H2, a second embedded layer 14B2 with a thickness of 50 nm is grown. The growth of the second embedded layer 14B2 is carried out as follows: after cooling the substrate temperature to 820 °C (the second embedding temperature), trimethylgallium (TEG) and trimethylindium (TMI) are supplied as the supply sources of group III atoms, and NH3 is supplied as the nitrogen source. In addition, the second embedding temperature is a temperature lower than the first embedding temperature, which is above 700 °C and lower than 900 °C.

[0120] In addition, the In component of the second embedded layer 14B2 in this embodiment is 2% (i.e., Ga 0.98 In 0.02 N layer). The second embedded layer 14B2 functions as a light distribution adjustment layer for adjusting the coupling efficiency (light field) of light with the photonic crystal layer 14P.

[0121] Through the above embedding process, a photonic crystal layer 14P with a double lattice structure is formed, in which a pore pair 14K composed of a main air hole 14K1 and a sub-air hole 14K2 is arranged at each square lattice point.

[0122] [S4: Light-emitting layer formation process]

[0123] Next, a multi-quantum well (MQW) layer is grown as the light-emitting layer, that is, the active layer 15. The barrier layer and the well layer of the MQW are GaN and InGaN respectively. The growth of the barrier layer is carried out as follows: after cooling the substrate to 820 °C, trimethylgallium (TEG) is supplied as the supply source of group III atoms, and NH3 is supplied as the nitrogen source. In addition, the growth of the well layer is carried out as follows: at the same temperature as the barrier layer, TEG and trimethylindium (TMI) are supplied as the supply sources of group III atoms, and NH3 is supplied as the nitrogen source. The center wavelength of the PL (Photoluminescence) emission from the active layer in this embodiment is 412 nm.

[0124] [S5: p-guiding layer formation process]

[0125] After the growth of the active layer, the substrate was heated to 1050 °C, and GaN was grown as the p-guide layer 16 with a layer thickness of 120 nm. The p-guide layer 16 was grown by supplying TMG and NH3 without doping dopants.

[0126] [S6: Electron blocking layer formation process]

[0127] After the growth of the p-guide layer 16, an electron blocking layer (EBL) 17 was grown while maintaining the substrate temperature at 1050 °C. The growth of the EBL 17 was carried out by supplying TMG and TMA as group III atomic sources and supplying NH3 as a nitrogen source. In addition, Cp2Mg was supplied as a p-dopant. Thus, an EBL 17 with an Al composition of 18% and a layer thickness of 15 nm was formed.

[0128] [S7: p-cladding layer formation process]

[0129] After the growth of the electron blocking layer (EBL) 17, a p-cladding layer 18 was grown while maintaining the substrate temperature at 1050 °C. The growth of the p-cladding layer 18 was carried out by supplying TMG and TMA as group III atomic sources and supplying NH3 as a nitrogen source. In addition, Cp2Mg was supplied as a p-dopant. Thus, a p-cladding layer 18 with an Al composition of 6% and a layer thickness of 600 nm was formed. In addition, when activation was carried out at 850 °C for 10 minutes in an N2 atmosphere after growth, the carrier concentration of the p-cladding layer (p-AlGaN) 18 was 2×10 17 cm -3 .

[0130] [S8: p-contact layer formation process]

[0131] After the growth of the p-cladding layer 18, a p-contact layer 19 was grown while maintaining the substrate temperature at 1050 °C. The growth of the p-contact layer 19 was carried out by supplying TMG as a group III atomic source and supplying NH3 as a nitrogen source. In addition, Cp2Mg was supplied as a dopant.

[0132] [S9: Electrode formation process]

[0133] The surface of the p-contact layer 19 of the substrate with the grown epitaxial growth layer was pasted onto the support substrate, and the substrate 12 was thinned to a specified thickness using a grinding device.

[0134] Then, a mask covering areas other than the element isolation grooves was formed on the p-contact layer 19 side, and etching was carried out until the n-cladding layer 13 or the substrate 12 was exposed. Then, the mask was removed, and the support substrate was detached to form element isolation grooves.

[0135] [S10: Electrode formation process]

[0136] (Anode electrode formation)

[0137] By the electron beam evaporation method, a palladium (Pd) film and a gold (Au) film were sequentially formed on the surface of the epitaxial growth substrate 12 as the p-electrode 20B. The formed electrode metal film was patterned into 200×200 μm by photolithography 2 to form the p-electrode 20B.

[0138] (Cathode electrode formation)

[0139] Next, by the electron beam evaporation method, Ti and Au were sequentially formed on the back surface of the substrate 12 to form the n-electrode 20A.

[0140] [S11: Protective film formation process]

[0141] The lower surface of the substrate on which the electrode formation was completed was pasted on the support substrate to form a mask covering the anode electrode. Then, an SiO2 film as a protective film was formed on the upper surface and side surfaces of the element by sputtering.

[0142] [S12: Singulation process]

[0143] Finally, laser scribing was performed along the center line of the substrate separation groove to obtain the singulated PCSEL element (hereinafter, referred to as the PCSEL element or simply PCSEL) 10.

[0144] 2. Main air hole and sub-air hole

[0145] In order to confirm the shape of the embedded air holes in this embodiment, the stacked structure was processed from the surface by a focused ion beam (FIB) until the air holes in the air hole layer were exposed, and then SEM observation was performed. Figure 5 The upper surface SEM image in shows the air hole shapes of the main air hole 14K1 and the sub-air hole 14K2 having a size smaller than that of the main air hole 14K1 at this time. In addition, for the sub-air hole 14K2, at least one of the air hole diameter and depth may be smaller than that of the main air hole 14K1.

[0146] In addition,[[]] Figure 6A shows Figure 5 the SEM image of the cross section at line A-A of Figure 6B shows Figure 5 the SEM image of the cross section at line B-B of

[0147] As Figure 5 shown, the major axis LK1 of the main air hole 14K1 is 75.2 nm, the minor axis WK1 is 45 nm, the ratio of the major axis to the minor axis (major axis / minor axis) RK1 = 1.67, the major axis LK2 of the sub-air hole 14K2 is 45.8 nm, the minor axis WK2 is 39.2 nm, and the ratio of the major axis to the minor axis (major axis / minor axis) RK2 = 1.17.

[0148] As shown Figure 6A , Figure 6B in the figure, the depth DK1 of the main air hole 14K1 is 102 nm, and the depth DK2 of the sub-air hole 14K2 is 78.5 nm.

[0149] As described above, it can be confirmed that a photonic crystal layer 14P is formed, in which a pair of air holes composed of the main air hole 14K1 and the sub-air hole 14K2 is arranged at each square lattice point with a period PC = 164 nm. That is, the main air hole 14K1 is arranged at the square lattice point with the period PC, and the sub-air hole 14K2 is arranged at the square lattice point with the same period PC. Moreover, the pair of air holes is arranged so that the distance (distance between the centers of gravity) between the center of gravity D1 of the main air hole 14K1 and the center of gravity D2 of the sub-air hole 14K2 is Δx in the x direction and Δy (constant) in the y direction.

[0150] In addition, in this specification, the "distance between the centers of gravity" of the main air hole and the sub-air hole refers to the distance between the center of gravity axis of the main air hole and the center of gravity axis of the sub-air hole, which is represented by the distances by which the sub-air hole and the main air hole are spaced apart in the x direction and the y direction.

[0151] In addition, the main air hole 14K1 and the sub-air hole 14K2 have a flat hexagonal prism shape with the long axis parallel to the <11 - 20> axis. Moreover, {1 - 102} facets appear at the bottoms (substrate 12 side) of the main air hole 14K1 and the sub-air hole 14K2, and the portions other than the bottoms are in the shape of a flat hexagonal prism.

[0152] Specifically, the distances Δx and Δy between the center of gravity D1 of the main air hole 14K1 and the center of gravity D2 of the sub-air hole 14K2 are both 65.4 nm (Δx = Δy = 0.4 × PC), and there is no change compared with before embedding. In addition, the long axes of the main air hole 14K1 and the sub-air hole 14K2 are arranged parallel to the <11 - 20> axis (i.e., the a axis).

[0153] In addition, in this specification, the "long axis or short axis" of the air hole (or hole) refers to the long axis or short axis of the cross-section (opening surface) of the air hole in the plane parallel to the photonic crystal layer.

[0154] In addition, the percentage of the value obtained by dividing the area of the air hole observed from the direction orthogonal to the plane of the photonic crystal layer 14P by the square of the period PC of the air hole is called the air hole filling factor FF (filling factor). The air hole filling factors FF1 and FF2 of the main air hole 14K1 and the sub-air hole 14K2 are calculated, and the results are FF1 = 10.5% and FF2 = 5.1%.

[0155] 3. Element characteristics, evaluation

[0156] 3.1 Double lattice structure and single lattice structure

[0157] (1) Comparative Example 1

[0158] As Comparative Example 1 of the PCSEL element 10 of the present embodiment, a PCSEL element having a single air hole (single lattice photonic crystal) formed at a lattice point was fabricated. Since only S3b (air hole forming process) is different from the above manufacturing process, this will be described.

[0159] Figure 7 It is an SEM image showing the cylindrical holes CH formed on the GaN surface portion in Comparative Example 1. Specifically, it has a circular opening with a diameter of 80 nm, and the holes CH are arranged at square lattice points with a period PC = 164 nm in the x and y directions.

[0160] More specifically, a resist was patterned such that the x-axis as the air hole arrangement direction was parallel to the <1-100> axis (i.e., the m-axis), and the y-axis was parallel to the <11-20> axis (i.e., the a-axis). Then, dry etching using an ICP-RIE apparatus was performed to form cylindrical air holes 14C arranged in a square lattice pattern in the x and y directions. The diameter of the cylindrical air holes 14C was 79 nm, and the period PC = 164 nm.

[0161] (2) Threshold Gain (Coupled Wave Theory)

[0162] Based on the electric field intensity distribution of the fundamental mode in the structures of Example 1 and Comparative Example 1, the optical confinement factor (Γact) of the active layer and the optical confinement factor (Γmg) of the layer doped with Mg (p contact layer, p cladding layer, electron blocking layer) were estimated. In addition, using the two-dimensional coupled wave theory, the in-plane resonator loss (α p ) and the resonator loss (α n ) in the direction perpendicular to the photonic crystal layer 14P of the photonic crystal layer 14P were estimated. They are shown in Table 1.

[0163] In Example 1 and Comparative Example 1, the absorption coefficient αmg of the layer doped with Mg was estimated to be 160 cm -1 . Based on Γmg and αmg, the absorption loss αi in each structure satisfying the following (Equation 1) is the value shown in Table 1.

[0164] αi = Γmg × αmg (Equation 1)

[0165] The threshold gain Gth of the laser is obtained by (Equation 2). As shown in Table 1, it was estimated to be 1119 cm -1 in Example 1 and 724 cm -1 in Comparative Example 1.

[0166] Γact Gth = α p +α n+αi (Equation 2)

[0167] [Table 1]

[0168] Table 1. Optical losses in Example 1 and Comparative Example 1

[0169] <![CDATA[Γ act > <![CDATA[Γ mg > <![CDATA[α p > <![CDATA[α n > <![CDATA[α i > <![CDATA[G th > Example 1 3.96％ 11.24％ <![CDATA[12.2cm -1 > <![CDATA[14.6cm -1 > <![CDATA[18.0cm -1 > <![CDATA[1119cm -1 > Comparative Example 1 3.69％ 8.61％ <![CDATA[10.8cm -1 > <![CDATA[2.36cm -1 > <![CDATA[13.8cm -1 > <![CDATA[724cm -1 >

[0170] In Table 1, α of Example 1 n is greater than α of Comparative Example 1 n . This is because the double lattice structure destroys the rotational symmetry of the lattice point structure. In Comparative Example 1, since the lattice point structure has a two-fold rotational symmetry, the light diffracted in the vertical direction in the light propagating in the pore layer is canceled out due to destructive interference. In Example 1, since the rotational symmetry becomes lower, this destructive interference becomes weaker and more light is diffracted in the vertical direction. That is, α n increases. In other words, in order to increase α n , it is preferable that the lattice point structure has a one-fold rotational symmetry, and it is sufficient that the pore groups of the main pores 14K1 and the sub-pores 14K2 have the same shape or arrangement when rotated 360°.

[0171] (3) Light output characteristics, emission spectrum

[0172] Figure 8A Shows the I-L characteristics (current-light output characteristics) of the PCSEL element 10 of Example 1 and the PCSEL element of Comparative Example 1, Figure 8B shows the emission spectrum near the threshold current. In addition, the measurement is performed by driving with a pulsed current having a pulse width of 100 ns and a pulse period of 1 kHz.

[0173] The PCSEL element 10 of Example 1 performs single-mode laser oscillation with a threshold current of 1.24 A (threshold current density: 3.9 kA / cm 2 ). On the other hand, the PCSEL element of Comparative Example 1 performs single-mode laser oscillation with a threshold current of 0.71 A (threshold current density: 2.2 kA / cm 2 ). The threshold current of Example 1 is larger than that of Comparative Example 1 because the threshold gain Gth in Table 1 increases. In Example 1 and Comparative Example 1, the increase ratio of the threshold gain Gth is approximately the same as the increase ratio of the threshold current, and the increase in the threshold current is considered to be caused by the increase in resonator loss and absorption loss, and it is considered that even when the double lattice structure is introduced as in Example 1, it does not affect the quality of the active layer.

[0174] On the other hand, it is known that the slope efficiency of the PCSEL element 10 in Example 1 is 0.23 W / A, which is significantly increased compared to 0.10 W / A in Comparative Example 1. This is because, in Example 1, as described above, α n (i.e., the leakage of light in the vertical direction = the light component that functions as the output) is large, so the light extracted as the output is large. That is, by making the lattice points in the pore layer have a double lattice structure, a larger output can be obtained with a smaller current.

[0175] 3.2 Configuration relationship between main pores and sub-pores in the double lattice structure

[0176] [Example 2]

[0177] (1) Example 2 and Comparative Example 2

[0178] In order to evaluate the surface shape after embedding by introducing a double lattice structure, a photonic crystal layer having two structures was fabricated, and the processes up to S3d were carried out in the same manner as in the above-described example to embed pores.

[0179] More specifically, two structures in which the main pores and the sub-pores have the same size and the same shape, but the major axis directions of the main pores and the sub-pores differ by 90° were studied.

[0180] Figure 9A is an SEM image of the upper surface of the main hole 14H1 and the sub-hole 14H2 formed on the GaN surface portion in the structure (Structure A) formed in the same manner as in Example 1 above. Specifically, in Structure A (Example 2), a pair of holes composed of an elliptical cylinder-shaped main hole 14H1 with a major axis / minor axis ratio of 2.75 (=79.8 nm / 29 nm) and an elliptical cylinder-shaped sub-hole 14H2 with a major axis / minor axis ratio of 1.14 (=42.8 nm / 37.6 nm) is formed in a square lattice pattern with a period PC = 164 nm.

[0181] Figure 9B is an SEM image of the upper surface of the main hole CH1 and the sub-hole CH2 formed on the GaN surface portion in Comparative Example 2. In Comparative Example 2 (Structure B), a pair of holes composed of an elliptical cylinder-shaped main hole CH1 with a major axis / minor axis ratio of 2.76 (=79.4 nm / 28.8 nm) and an elliptical cylinder-shaped sub-hole CH2 with a major axis / minor axis ratio of 1.10 (=41.8 nm / 37.9 nm) is formed in a square lattice pattern with a period PC = 164 nm.

[0182] In Structure A ( Figure 9A ), the major axes of the main hole 14H1 and the sub-hole 14H2 are arranged parallel to the <11-20> axis (i.e., the a axis). On the other hand, in Structure B ( Figure 9B)In it, the major axes of the main hole CH1 and the sub-hole CH2 are arranged to be orthogonal to the <11-20> axis (i.e., the a-axis).

[0183] That is, Structure A (Example 2) and Structure B (Comparative Example 2) have main holes and sub-holes with substantially the same size and the same shape, but the major axis direction of the holes in Structure B (Comparative Example 2) is different from that in Structure A (Example 2) by 90°.

[0184] Therefore, by embedding the main hole 14H1 and the sub-hole 14H2 of Structure A, a photonic crystal layer 14P is obtained in which the major axes of the main air hole 14K1 and the sub-air hole 14K2 are arranged parallel to the <11-20> axis (see Figure 11A ). In addition, by embedding the main hole CH1 and the sub-hole CH2 of Structure B, a photonic crystal layer is obtained in which the major axes of the main air hole CK1 and the sub-air hole CK2 are arranged orthogonal to the <11-20> axis (see Figure 11B ).

[0185] (2) Surface roughness of the embedding layer

[0186] Figure 10A 、 Figure 10B These are the images of an atomic force microscope (AFM: Atomic Force Microscope) showing the surface morphology of the embedding layer after embedding the main air hole and the sub-air hole in the cases of Structure A (Example 2) and Structure B (Comparative Example 2), respectively. In addition, the horizontal axis direction of the AFM image is the m-axis, and the vertical axis direction is the a-axis.

[0187] As Figure 10A shown, when the major axis of each air hole is parallel to the a-axis (<11-20> axis) (Structure A: Example 2), a flat surface with a surface roughness (RMS) of 0.594 nm is obtained.

[0188] On the other hand, as Figure 10B shown, when the major axis of each air hole is orthogonal to the a-axis (Structure B: Comparative Example 2), undulations with a height of about 7 nm appear on the surface, and the surface roughness (RMS 0.836 nm) is larger than that in the case of Structure A (Example).

[0189] If an active layer is grown on an embedding layer with such large irregularities on the surface of the embedding layer, compositional non-uniformity of In will occur at the locations with irregularities, and the quality of the active layer will deteriorate. Therefore, since the threshold current increases, it is preferable that the major axis of the air hole of the photonic crystal layer is parallel to the a-axis.

[0190] Figure 11A 、 Figure 11BIt is a top view schematically showing the shape change of the hole during the formation of the embedding layer. Referring to these figures, the following examines the case where the major axis of the hole is parallel to the a-axis of the crystal orientation and the case where they are orthogonal, and the case where the surface roughness of the embedding layer is different.

[0191] When embedding holes in group-III nitrides, due to mass transfer, the hole shape deforms into a shape composed of thermally stable planes, forming air holes. That is, in the +c plane substrate, the side surface of the air hole changes its shape to the {1-100} plane (i.e., the m plane). That is, the shape changes from an elliptical columnar shape to a flat hexagonal columnar shape with the side surface composed of the m plane.

[0192] Figure 11A Schematically shows the shape change of the air hole in the case where the major axis of the elliptical columnar hole is parallel to the a-axis (<11-20> axis) (Structure A). After deformation, the air hole sizes of holes 14H1 and 14H2 decrease, and group-III nitride atoms corresponding to the change amount are supplied from the surrounding crystal parts by mass transfer (arrows in the figure). Then, the shape changes to air holes 14K1 and 14K2, which are flat hexagonal prisms inscribed in the shapes of the original holes 14H1 and 14H2.

[0193] On the other hand, Figure 11B Schematically shows the shape change of the air hole in the case where the major axis of the elliptical columnar hole is perpendicular to the a-axis (Structure B). Due to mass transfer, the air hole sizes of holes CH1 and CH2 decrease (arrows in the figure). This shape change is larger than the case of the air hole whose major axis is parallel to the a-axis ( Figure 11A ).

[0194] In a multi-lattice photonic crystal, the distance between air holes is shorter than that in a single-lattice photonic crystal. Therefore, adjacent air holes (i.e., the main air hole and the sub-air hole) are arranged at a distance of approximately the air hole size. Therefore, when the shape change of the air hole caused by mass transfer occurs, the shape changes of adjacent air holes interfere with each other. In the part where the shape change interferes and the part where it does not interfere, large irregularities (height differences) are formed on the embedding surface. Therefore, as Figure 11B shown, when the major axis of the hole is orthogonal to the a-axis, due to the large shape change, surface roughness is generated. On the other hand, it is considered that when the major axis of the hole is parallel to the a-axis, the shape change can be suppressed to a minimum, and a flat surface can be obtained after embedding.

[0195] (3) Positional relationship between the main air hole and the sub-air hole and resonator loss

[0196] In the air hole layer (photonic crystal layer), when the air holes are arranged in a square lattice, in order to prevent the non-uniform distribution of light depending on the direction in the two-dimensional photonic crystal and stably obtain laser oscillation at a single wavelength, it is preferable to have the same feedback effect (diffraction efficiency) in the x-axis direction and the y-axis direction.

[0197] That is, the two-dimensional photonic crystal forming the air hole layer is preferably symmetric with respect to an axis inclined 45° from the x-axis and y-axis of the square lattice. When the main air holes 14K1 and the sub air holes 14K2 are symmetric structures with respect to an axis inclined 45° from the x-axis and y-axis, it is preferable that the distance Δx between the centers of gravity in the x-axis direction and the distance Δy between the centers of gravity in the y-axis direction between the main air holes 14K1 and the sub air holes 14K2 are equal (Δx = Δy).

[0198] Figure 12A 、 Figure 12B Shows the resonator loss α in the directions perpendicular and horizontal to the photonic crystal layer 14P when the distance (interval) Δx, Δy between the centers of gravity of the main air holes 14K1 and the sub air holes 14K2 forming the photonic crystal layer 14P in the structure of Example 1 is Δx = Δy and varies from 0.0 PC to 0.5 PC (PC is the period of the square lattice). n 、α p . In addition, the horizontal axis represents the ratio d with respect to the period PC (that is, d = Δx / PC = Δy / PC).

[0199] In addition, Figure 12C shows R obtained according to the following (Equation 3). n That is, R n is the ratio of the resonator loss α n in the vertical direction to the total resonator loss (α p +α n ).

[0200] R n =α n / (α p +α n ) (Equation 3)

[0201] In a photonic crystal surface emitting laser, as shown in (Equation 4), the slope efficiency ηSE is proportional to the ratio of α i in the total loss including the absorption loss α n (resonator loss in the vertical direction).

[0202] [Mathematical formula 1]

[0203] ηSE∝α n / (α p +α n +α i ) (Equation 4)

[0204] Therefore, assuming that the absorption loss α i caused by the constituent materials can be made zero, then ηSE is proportional to R nIs proportional to. That is, in order to improve the emission efficiency of the photonic crystal surface emitting laser (i.e., ηSE) and obtain a photonic crystal surface emitting laser with high output, it is desirable to increase R n .

[0205] According to Table 1, R in the existing single-lattice photonic crystal surface emitting laser (Comparative Example 1) n is about 0.18. In the double-lattice photonic crystal surface emitting laser (Example 1), in order to make R n higher than that of the existing laser (R n = 0.18), referring to Figure 12C , the relative position d (=Δx / PC = Δy / PC) of the sub-air hole with respect to the main air hole is preferably 0.06 or more or 0.47 or less.

[0206] (4) Oscillation mode

[0207] Referring to Figure 12C , when the distances (intervals) Δx and Δy between the centers of gravity of the main air hole 14K1 and the sub-air hole 14K2 (Δx = Δy) are 0.28×PC and 0.40×PC, R n changes discontinuously. This is because the oscillation mode changes with this distance between the centers of gravity as the boundary.

[0208] Figure 13 Shows the photonic band structure near the Γ point of the square lattice photonic crystal. In the photonic crystal surface emitting laser, the standing wave state of light at the band edge of the Γ point of the photonic band structure of the air hole layer is used as the resonance effect. At the band edge of the Γ point, there are four band edge modes A, B, C, and D (represented by black dots) starting from the low-frequency side. Laser oscillation can be obtained in the mode with the lowest threshold gain (smaller resonator loss) among these four band edge modes.

[0209] Figure 14 Shows the threshold gain (resonator loss) of each mode obtained by the coupled wave theory when the distances Δx and Δy between the centers of gravity are changed in Example 1. It can be seen that as the mode with the smallest threshold gain, it is mode A when d≤0.28, mode D when 0.28PC<d<0.40, and mode B when 0.40≤d.

[0210] Figure 15Schematically shows the refractive index, carrier density, and photon density in the current injection region during laser oscillation of a surface-emitting laser. In group III nitride semiconductors, generally, the refractive index of the current injection region decreases due to the carrier plasma effect. On the other hand, in a semiconductor laser, in the center of the resonator where the photon density is high, the stimulated emission rate becomes high and the carrier density becomes low. In addition, the temperature in the central part rises due to heat generation. Therefore, the refractive index of the central part of the current injection region is higher than that of its surroundings.

[0211] Figure 16A Schematically shows in the case of band-edge modes A and B, Figure 16B Schematically shows the frequencies of the photon band edges at the Γ point near the current injection region during current injection in the case of band-edge modes C and D.

[0212] The frequency ω is expressed as in (Equation 5) using the refractive index n, the speed of light c, and the wave number k.

[0213] ω = c / n × k (Equation 5)

[0214] According to (Equation 5), when the refractive index distribution changes as shown during current injection (laser oscillation), the frequency distributions of the A, B, C, and D modes of each band-edge mode also change as shown with the change in the refractive index (from a trapezoidal shape to a trapezoidal shape with a central depression). Figure 15 shown, Figure 16A and Figure 16B shown and change with the change in the refractive index (from a trapezoidal shape to a trapezoidal shape with a central depression).

[0215] As Figure 16A shown, in the case of band-edge modes A and B (hereinafter simply referred to as modes A and B), in the central part of the current injection region, the oscillation mode frequency exists within the photon bandgap. Therefore, the presence of photons at the central part of the injection region can be suppressed, and photons are generated in a region outside the central part of the injection region.

[0216] Figure 17A Schematically shows the refractive index, carrier density, and photon density in the current injection region during the oscillation operation in band-edge modes A and B. The case considering the photon band effect is shown by a solid line, and the case not considering the photon band effect is shown by a dashed line.

[0217] When considering the photon band effect, as described above, in modes A and B, the photon distribution is in a wider region, and as the injection current increases, the photon density becomes flat throughout the current region.

[0218] Accordingly, the carrier density and the refractive index are also homogenized throughout the current injection region. Therefore, when performing the oscillation operation in modes A and B, even when performing a high-output operation by injecting a large current, as the current increases, the photon density distribution becomes flat throughout the injection region, and thus the emitted light beam has a stable beam pattern.

[0219] On the other hand, as Figure 16B shown, in the case of the edge modes C and D, in the region outside the central part of the current injection region, the oscillation mode frequency exists within the bandgap. Therefore, photons are locally present in the central part of the injection region.

[0220] Figure 17B Schematically shows the refractive index, carrier density, and photon density of the current injection region when performing the oscillation operation in the edge modes C and D. The case considering the photon band effect is shown by a solid line, and the case not considering the photon band effect is shown by a dashed line.

[0221] When considering the photon band effect, photons are concentrated and locally present in the central part of the current injection region. Therefore, the carrier density and the refractive index also change significantly locally in the central part of the current injection region and have a non-uniform distribution in the current injection region.

[0222] Therefore, when performing the oscillation operation in the edge modes C and D, if a large current is injected for a high-output operation, as the current increases, the photon density distribution is localized and concentrated, and thus the emitted light beam has an unstable beam pattern. In addition, if a large current is injected, the distribution of the carrier density and the refractive index has a large non-uniformity, and thus the oscillation operation is also likely to be multimoded, and a stable oscillation operation cannot be obtained.

[0223] As described above, in order to obtain stable oscillation when injecting a high current, it is preferable to perform the oscillation in modes A and B, and the relative position d (=Δx / PC =Δy / PC) of the secondary air hole 14K2 with respect to the primary air hole 14K1 is preferably 0.06PC to 0.28PC (0.06≤d≤0.28) or 0.40PC to 0.47PC (0.40≤d≤0.47).

[0224] [Example 3]

[0225] In Example 3, a PCSEL element 10 having an air hole layer (photonic crystal layer) with a dual lattice structure composed of two main air holes 14K1 and secondary air holes 14K2 in the shape of regular hexagonal prisms was studied.

[0226] 1. Manufacturing process

[0227] Hereinafter, the manufacturing process of the PCSEL element 10 of Example 3 will be described in detail. In addition, the points different from and the main points of the manufacturing process of the above-described example will be described. In addition, the structure of the PCSEL element 10 and the layer configuration of the semiconductor structure layer 11 are the same as those Figure 1A shown.

[0228] [S3b: Hole and air hole formation process]

[0229] The substrate of the growth layer on which the n-type GaN layer is grown as the preparation layer of the n-guiding layer 14 is cleaned to obtain a clean surface. In addition, this n-type GaN growth layer is a preparation layer for forming a layer composed of the lower guiding layer 14A and the photonic crystal layer 14P.

[0230] After cleaning the substrate of the growth layer to obtain a clean surface, a silicon nitride film (Si x N y ) is formed by plasma CVD. An electron beam lithography resist is coated thereon by spin coating, and it is put into an electron beam (EB) lithography apparatus for patterning of a two-dimensional periodic structure.

[0231] Thus, the following patterning is performed: A pair of openings composed of a main opening K1 having a substantially circular shape and a sub-opening K2 smaller than the main opening K1 is two-dimensionally arranged in a square lattice pattern in the plane of the resist with a period PC = 164 nm (see Figure 3 ).

[0232] More specifically, the centroids CD1 of the main openings K1 are arranged at square lattice points with a period PC = 164 nm in two directions (x direction and y direction) orthogonal to each other. Similarly, for the sub-openings K2, their centroids CD2 are arranged at square lattice points with a period PC = 164 nm in the x direction and the y direction.

[0233] In addition, the major axis of the main opening K1 is 76 nm and the minor axis is 66 nm (major axis / minor axis = 1.15), and the major axis of the sub-opening K2 is 59 nm and the minor axis is 51 nm (major axis / minor axis = 1.12). The patterning is performed such that the long axis of each opening is parallel to the <11-20> axis (i.e., the a axis).

[0234] The patterning is performed such that the distance Δx = Δy between the centroids of the main opening K1 and the sub-opening K2 in the x direction and the y direction becomes 65.6 nm (= 0.4 × 164 nm).

[0235] After developing the patterned resist, the Si x N yThe film is dry-etched. Thus, the main openings K1 and the sub-openings K2 arranged at square lattice points with a period of 164 nm are formed to penetrate the Si x N y film.

[0236] In addition, the main openings K1 and the sub-openings K2 have an elliptical shape slightly deviated from a perfect circular shape, but may also be formed into a perfect circular shape.

[0237] Next, the resist is removed, and the patterned Si x N y film is used as a hard mask to form holes on the GaN surface. The GaN is dry-etched using a chlorine-based gas by an ICP-RIE apparatus, thereby forming a plurality of hole pairs 14H (main holes 14H1 and sub-holes 14H2) perpendicular to the GaN surface.

[0238] [S3c: Cleaning process]

[0239] After the substrate on which the holes 14H1 and 14H2 are formed is degreased and cleaned, the Si x N y film is removed with buffered hydrofluoric acid (HF). Figure 18 The SEM image of the GaN surface at this time is shown.

[0240] As Figure 18 shown, a plurality of hole pairs 14H (main holes 14H1 and sub-holes 14H2) are formed in a two-dimensional square lattice arrangement with a period PC of 164 nm, that is, two-dimensionally arranged at square lattice points. The holes 14H1 and 14H2 are substantially cylindrical holes opening on the upper surface (GaN surface).

[0241] More specifically, the major axis length LH1 of the opening of the main hole 14H1 on the GaN surface is 76 nm, the minor axis length WH1 is 68 nm, that is, RH1 (= major axis / minor axis) = 1.12, and the major axis length LH2 of the opening of the sub-hole 14H2 is 59 nm, the minor axis length WH2 is 53 nm, RH2 (= major axis / minor axis) = 1.11.

[0242] At this time, the intervals between the center of gravity CD1 of the main hole 14H1 and the center of gravity CD2 of the sub-hole 14H2 in the x-direction and the y-direction are 65.3 nm (= 0.4 × PC), respectively. In addition, the major axes of the main hole 14H1 and the sub-hole 14H2 are arranged parallel to the <11-20> axis (i.e., the a-axis).

[0243] In addition, the main hole 14H1 and the sub-hole 14H2 have an elliptical cylindrical shape slightly deviated from a perfect cylindrical shape, but may also be formed into a perfect cylindrical shape.

[0244] [S3d: Embedding layer formation process]

[0245] The substrate is re-introduced into the reactor of the MOVPE apparatus, ammonia (NH3) is supplied, and the temperature is raised to 950 °C (the first embedding temperature). Then, trimethylgallium (TMG) and NH3 are supplied, and the openings of the main hole 14H1 and the sub-hole 14H2 are closed to form the first embedding layer 14B1.

[0246] In this temperature range, since N atoms are attached to the outermost surface of the growth substrate, the N-polar surface is selectively grown. Therefore, the {1-101} facets are selectively grown on the surface. The opposing {1-101} facets collide with each other, whereby the holes are closed and embedded in the GaN layer.

[0247] Next, after closing the main hole 14H1 and the sub-hole 14H2, a second embedding layer 14B2 with a thickness of 50 nm is grown. The growth of the second embedding layer 14B2 is carried out as follows: after cooling the substrate temperature to 820 °C (the second embedding temperature), triethylgallium (TEG) and trimethylindium (TMI) are supplied as the supply sources of group III atoms, and NH3 is supplied as the nitrogen source.

[0248] In addition, the In composition of the second embedding layer 14B2 is 2% (i.e., Ga 0.98 In 0.02 N layer). The second embedding layer 14B2 functions as a light distribution adjustment layer for adjusting the coupling efficiency (light field) of light with the photonic crystal layer 14P.

[0249] [S4: Light-emitting layer formation process]

[0250] Next, a multi-quantum well (MQW) layer is grown as the light-emitting layer, i.e., the active layer 15. More specifically, similar to the above-described embodiment, the barrier layer and the well layer of the MQW are GaN and InGaN, respectively. The growth of the barrier layer is carried out as follows: after cooling the substrate to 820 °C, triethylgallium (TEG) is supplied as the supply source of group III atoms, and NH3 is supplied as the nitrogen source. In addition, the growth of the well layer is carried out as follows: at the same temperature as the barrier layer, TEG and trimethylindium (TMI) are supplied as the supply sources of group III atoms, and NH3 is supplied as the nitrogen source. The center wavelength of the PL emission from the active layer in this embodiment is 412 nm.

[0251] The processes after S5 (p-side guiding layer formation process) are the same as the above-described manufacturing processes to form the PCSEL element 10 of Example 3.

[0252] 2. Main air hole and sub-air hole

[0253] In order to confirm the shape of the air holes formed by embedding in the embodiment, the layered structure is processed from the surface by FIB until the air holes in the air hole layer are exposed, and then SEM observation is carried out.Figure 19A The SEM image of the upper surface in shows the pore shapes of the main pores 14K1 and the secondary pores 14K2 that are smaller in size than the main pores 14K1 at this time. In addition, for the secondary pores 14K2, it is sufficient that at least one of the pore diameter and the depth is smaller than that of the main pores 14K1.

[0254] In addition, Figure 19B is the SEM image of the cross-section at line A-A showing Figure 19A and Figure 19C is the SEM image of the cross-section at line B-B showing Figure 19A .

[0255] According to Figure 19A , it can be confirmed that the main pores 14K1 and the secondary pores 14K2 have a hexagonal shape. In addition, through SEM observation, the major axis length LK1 of the main pores 14K1 is 57.2 nm, the minor axis length WK1 is 49.5 nm, and the ratio of the major axis to the minor axis (major axis / minor axis) RK1 = 1.15. In addition, the depth DK1 of the main pores 14K1 is 91.3 nm.

[0256] In addition, the major axis length LK2 of the secondary pores 14K2 is 43.5 nm, the minor axis length WK2 is 37.7 nm, and the ratio of the major axis to the minor axis (major axis / minor axis) RK2 = 1.15. In addition, the depth DK2 of the secondary pores 14K2 is 79.4 nm.

[0257] The ratio of the major axis to the minor axis of a regular hexagon is RR = 2 / 3 1 / 2 = 1.15. Therefore, based on this ratio RK1 of the main pores 14K1 and this ratio RK2 of the secondary pores 14K2, it can be confirmed that the main pores 14K1 and the secondary pores 14K2 have a regular hexagonal prism shape.

[0258] In addition, the distances (distance between centroids) Δx and Δy between the centroid D1 of the main pores 14K1 and the centroid D2 of the secondary pores 14K2 are 65.4 nm (= 0.4 × PC), respectively, and there is no change compared with before embedding.

[0259] In addition, the major axes of the main pores 14K1 and the secondary pores 14K2 are arranged parallel to the <11-20> axis (i.e., the a axis).

[0260] 3. Element characteristics, evaluation

[0261] (1) Comparative Example 1 and Comparative Example 2

[0262] In the evaluation of the PCSEL element 10 of Example 3, it was compared with the PCSEL element of Comparative Example 1 having a single crystal lattice structure with a single pore formed at the lattice point. In addition, Example 3 was compared with the PCSEL element of Comparative Example 2 in which the major axis directions of the main pores and the secondary pores differ by 90°.

[0263] (2) Threshold gain (coupled wave theory)

[0264] Based on the electric field intensity distribution of the fundamental mode in the structures of Example 3 and Comparative Example 1, the optical confinement factor (Γact) of the active layer and the optical confinement factor (Γmg) of the layer doped with Mg (p-contact layer, p-cladding layer, electron blocking layer) were estimated. Additionally, using the two-dimensional coupled wave theory, the resonator loss (α p ) in the in-plane direction of the photonic crystal layer 14P and the resonator loss (α n ) in the direction perpendicular to the photonic crystal layer 14P were estimated.

[0265] In Example 3 and Comparative Example 1, the absorption coefficient α of the layer doped with Mg mg was estimated to be 160 cm -1 . Based on the optical confinement factor (Γmg) and the absorption coefficient α mg , through the above (Equation 1), the absorption loss α i was the value shown in Table 2. The threshold gain Gth of the laser was obtained through the above (Equation 2). As shown in Table 2, it was estimated to be 1068 cm -1 in Example 3 and 724 cm -1 in Comparative Example 1. They are summarized in Table 2.

[0266] [Table 2]

[0267] Table 2: Optical losses and threshold gains in Example 3 and Comparative Example 1

[0268] <![CDATA[Γ act > <![CDATA[Γ mg > <![CDATA[α p (α / / )]]> <![CDATA[α n (α⊥)]]> <![CDATA[α i > <![CDATA[G th > Example 3 3.78％ 9.40％ <![CDATA[10.5cm -1 > <![CDATA[14.9cm -1 > <![CDATA[15.0cm -1 > <![CDATA[1068cm -1 > Comparative Example 1 3.69％ 8.61％ <![CDATA[10.8cm -1 > <![CDATA[2.36cm -1 > <![CDATA[13.8cm -1 > <![CDATA[724cm -1 >

[0269] In Table 2, α n of Example 3 is greater than α n of Comparative Example 1. This is because the double lattice structure destroys the 90° rotational symmetry of the lattice point structure. In Comparative Example 1, since the lattice point structure has 90° rotational symmetry, the light diffracted in the vertical direction in the light propagating in the air hole layer is canceled out due to destructive interference.

[0270] In Example 3, since the 90° rotational symmetry is lower, this destructive interference becomes weaker and more light is diffracted in the vertical direction. That is, α n increases.

[0271] As described above, it can be confirmed that in Example 3 where the main air hole 14K1 and the sub air hole 14K2 have a regular hexagonal prism shape, compared with the photonic crystal layer of the single lattice structure, the light component propagating in the vertical direction also increases significantly.

[0272] (3) Light output characteristics, emission spectrum

[0273] Figure 20A Shows the I-L characteristics (current-optical output characteristics) of the PCSEL element 10 of Example 3 and the PCSEL element of Comparative Example 1. Figure 20B Shows the emission spectrum near the threshold current. In addition, the measurement was carried out by driving with a pulsed current having a pulse width of 100 ns and a pulse period of 1 kHz.

[0274] The PCSEL element 10 of Example 3 performs single-mode laser oscillation with a threshold current of 1.21 A (threshold current density: 3.8 kA / cm 2 ). On the other hand, the PCSEL element of Comparative Example 1 performs single-mode laser oscillation with a threshold current of 0.71 A (threshold current density: 2.2 kA / cm 2 ). The threshold current of Example 3 is larger than that of Comparative Example 1 because the threshold gain Gth shown in Table 2 increases.

[0275] In Example 3 and Comparative Example 1, the increase ratio of the threshold gain Gth is approximately the same as the increase ratio of the threshold current. The increase in the threshold current is considered to be caused by the increase in resonator loss and absorption loss, and it is considered that even when the double lattice structure is introduced as in Example 3, it does not affect the quality of the active layer.

[0276] On the other hand, it is known that the slope efficiency of the PCSEL element 10 of Example 3 is 0.35 W / A, which is significantly increased compared to 0.10 W / A of Comparative Example 1. This is because, in Example 3, as described above, α n (that is, the increase in the light propagating in the vertical direction) is large, so the light extracted as the output is large. That is, by making the lattice structure in the air hole layer a double lattice structure, a larger output can be obtained with a smaller current.

[0277] (4) Positional relationship between main air holes and sub-air holes and resonator loss

[0278] In Example 3, a PCSEL element is fabricated with an air hole layer having a double lattice structure composed of main air holes 14K1 and sub-air holes 14K2 in the shape of regular hexagonal prisms with two lattice points.

[0279] Figure 21A , Figure 21B Shows the resonator losses α n , α pIn addition, the horizontal axis represents the ratio d of the distance between centers of gravity (the interval between the main air hole and the sub air hole) Δx, Δy to the period PC of the square lattice (i.e., d = Δx / PC = Δy / PC).

[0280] In addition, in Figure 21C shows the center-of-gravity distance correlation of R obtained according to the above (Equation 3). That is, R n is the ratio of the resonator loss α n in the vertical direction to the total resonator loss (α n +α p +α n ).

[0281] In addition, in a photonic crystal surface emitting laser, as shown in the above (Equation 4), the slope efficiency ηSE is proportional to the ratio of α n (the resonator loss in the vertical direction) in the total loss including the absorption loss αi.

[0282] Therefore, assuming that the absorption loss αi caused by the constituent materials can be made zero, ηSE is proportional to R n . That is, in order to improve the emission efficiency of the PCSEL element (i.e., ηSE) and obtain a PCSEL element with high output, it is desirable to increase R n .

[0283] According to Table 2, R n in the existing single lattice structure PCSEL element (Comparative Example 1) is about 0.18. In the PCSEL element with a double lattice structure composed of a regular hexagonal prism-shaped main air hole and a sub air hole in Example 3, in order to make R n higher than that of the single lattice structure PCSEL element (R n = 0.18), referring to Figure 21C , the distance between the centers of gravity (relative position d) of the main air hole 14K1 and the sub air hole 14K2 (= Δx / PC = Δy / PC) is preferably 0.06 or more or 0.47 or less.

[0284] In addition, it is considered that by making the air hole shape a flat hexagonal prism shape with a large major axis / minor axis ratio, the four-fold (90°) rotational symmetry of the spatial refractive index distribution within the lattice point can be broken, but it is known that a relatively high R n can also be obtained even in a regular hexagonal prism-shaped air hole with a major axis / minor axis ratio as small as 1.15.

[0285] However, in a PCSEL element using a GaN-based material, in order to stably embed the air hole, it is preferable to change the side shape of the air hole to the thermally stable m-plane during growth. That is, the major axis / minor axis ratio of the air holes forming the air hole layer is preferably at least 1.15 or more.

[0286] (5) Oscillation mode

[0287] Figure 21D Shows the threshold gain (resonator loss) of each mode obtained by the coupled-wave theory when the relative position d (= Δx / PC = Δy / PC) of the sub-aperture 14K2 with respect to the main aperture 14K1 is changed in Example 3.

[0288] It can be seen that as the mode with the minimum threshold gain, when the relative position d is 0.24×PC or less (d ≤ 0.24), it is mode A; when it is in the range of 0.24PC to 0.28PC (0.24 < d ≤ 0.28), it is mode B; when it is in the range of 0.28PC to 0.34PC (0.28 < d < 0.34), it is mode C; when it is in the range of 0.34PC to 0.40PC (0.34 ≤ d < 0.40), it is mode D; and when it is 0.40PC or more (0.40 ≤ d), it is mode B.

[0289] In addition, as described with reference to Figure 16A 、 16B For obtaining stable oscillation when injecting a high current, it is preferable to oscillate in modes A and B.

[0290] (6) Aperture filling factor (FF: filling factor)

[0291] In the structure of Example 3, the resonator loss is obtained by the two-dimensional coupled-wave theory when the aperture filling factor FF2 of the sub-aperture 14K2 is fixed at 4.5% and the aperture filling factor FF1 of the main aperture 14K1 is changed in the range of 4.5% to 40%. Figure 22A and Figure 22B Show, respectively, with respect to the aperture filling factor ratio FF1 / FF2, R n and the sum of the resonator losses in the vertical and horizontal directions (α n +α p ).

[0292] In addition, as described above, in this specification, the aperture filling factor refers to the ratio of the area occupied by each aperture per unit area of the two-dimensional periodic arrangement. Specifically, if the areas of the main aperture 14K1 and the sub-aperture 14K2 in the aperture layer are set as S1 and S2 respectively, in the case of a square lattice (period PC), the aperture filling factor FF1 of the main aperture 14K1 = S1 / PC 2 , and the aperture filling factor FF2 of the sub-aperture 14K2 = S2 / PC 2 .

[0293] Generally, the photon band structure near the Γ point of a square lattice photonic crystal is as shown in the above Figure 13 , and there are four band-edge modes. As Figure 22A and Figure 22BAs shown, the edge mode with the minimum loss changes with the change in the pore filling ratio FF1 / FF2.

[0294] As described in detail in Example 1 and Example 2, in order to obtain stable oscillation when injecting a high current, it is preferable to perform oscillation in modes A and B. That is, in order to perform oscillation in modes A and B, as Figure 22A and Figure 22B shown, it is preferable that the pore filling ratio RF = FF1 / FF2 is in the range of 1.7 to 7.5, that is, 1.7 ≤ (FF1 / FF2) ≤ 7.5.

[0295] In addition, in the above embodiments, the cases where the main pores 14K1 and the sub-pores 14K2 have a flat hexagonal prism shape and a regular hexagonal prism shape are described, but the sub-pores 14K2 may also have a cylindrical shape with a circular cross-section, a regular hexagonal prism shape, etc.

[0296] In addition, the cases where the embedded main pores 14K1 have a flat hexagonal prism shape and a regular hexagonal prism shape are described, but it is not limited thereto. The main pores 14K1 may also be an elliptical cylinder shape, or may have an intermediate shape during the process of the pore changing from a cylindrical shape or an elliptical cylinder shape to a regular hexagonal prism shape or a flat hexagonal prism shape by epitaxial growth. Therefore, in this specification, "regular hexagonal prism shape, flat hexagonal prism shape or elliptical cylinder shape" includes the intermediate shape during the process of changing from a cylindrical shape or an elliptical cylinder shape to a regular hexagonal prism shape or a flat hexagonal prism shape.

[0297] In addition, when the main pores 14K1 have a regular hexagonal prism shape, a flat hexagonal prism shape or an elliptical cylinder shape with the major axis parallel to the <11-20> axis, the sub-pores 14K2 may also have a regular hexagonal prism shape, a flat hexagonal prism shape or an elliptical cylinder shape with the major axis parallel to the <11-20> axis.

[0298] In addition, in the above embodiments, the photonic crystal layer 14P in which a pair of pores composed of the main pores 14K1 and the sub-pores 14K2 is arranged at each square lattice point is described, but a pore group composed of the main pores 14K1, the sub-pores 14K2 and at least one pore may also be arranged at each square lattice point to form a multi-lattice photonic crystal layer.

[0299] In addition, the numerical values in the above embodiments are only examples and can be applied by appropriately changing them.

[0300] As described in detail above, according to the above-described present embodiment, it is possible to provide a photonic crystal surface-emitting laser (PCSEL) element and a manufacturing method thereof, in which the flatness of the surface of the embedded layer in which the multi-lattice photonic crystal is embedded is significantly improved.

[0301] In addition, it is possible to provide a photonic crystal surface emitting laser and a method for manufacturing the same, in which the photonic crystal surface emitting laser has a high quality and crystallinity of an active layer grown on a multi-lattice photonic crystal layer, a high light extraction efficiency, and can perform an oscillation operation with a low threshold current density and a high quantum efficiency.

[0302] Symbol Explanation

[0303] 10: PCSEL element; 11: semiconductor structure layer; 12: substrate; 13: first cladding layer; 14: first guiding layer; 14A: lower guiding layer; 14P: photonic crystal layer (PC layer); 14B: embedding layer; 15: active layer; 16: second guiding layer; 17: electron blocking layer; 18: second cladding layer; 19: contact layer; 20A: first electrode; 20B: second electrode; 20L: light emission region; 25: second embedding layer; CD1; CD2: center of gravity; K1 / K2: main / auxiliary opening; 14H1 / 14H2: main / auxiliary hole; 14K1 / 14K2: main / auxiliary air hole

Claims

1. A surface-emitting laser element composed of a group-III nitride semiconductor and having: A first guiding layer having a photonic crystal layer and an embedding layer, the photonic crystal layer being formed on the c-plane of the group-III nitride semiconductor and having air holes two-dimensionally periodically arranged in a plane parallel to the layer, and the embedding layer being formed on the photonic crystal layer to close the air holes; An active layer formed on the first guiding layer; And A second guiding layer formed on the active layer, An air hole group is arranged at each square lattice point in a plane parallel to the photonic crystal layer, and the air hole group includes at least a main air hole and a sub-air hole having an air hole diameter and depth smaller than those of the main air hole, The embedding and closing surfaces of the main air hole and the sub-air hole are located on the side closer to the active layer in the photonic crystal layer, The main air hole has a regular hexagonal prism shape, a flattened hexagonal prism shape, or an elliptical cylinder shape with its major axis parallel to the <11-20> axis.

2. The surface-emitting laser element according to claim 1, wherein The sub-air hole has a regular hexagonal prism shape, a flattened hexagonal prism shape, or an elliptical cylinder shape with its major axis parallel to the <11-20> axis.

3. The surface-emitting laser element according to claim 1, wherein The main air hole and the sub-air hole have a regular hexagonal prism shape with their major axes parallel to the <11-20> axis.

4. The surface-emitting laser element according to any one of claims 1 to 3, wherein The sub-air hole is arranged at a position where the center of gravity of the sub-air hole and the center of gravity of the main air hole are spaced apart in the <1-100> direction.

5. The surface-emitting laser element according to any one of claims 1 to 3, wherein The air hole group is arranged in the x-direction and the y-direction that are orthogonal to each other and have an angle of 45° with respect to the <11-20> axis and the <1-100> axis, The relative positions Δx and Δy of the sub-air hole with respect to the main air hole satisfy Δx = Δy, and when the period of the square lattice is set as PC and Δx = Δy = d×PC, 0.06 ≤ d ≤ 0.28 or 0.40 ≤ d ≤ 0.47 is satisfied.

6. The surface-emitting laser element according to any one of claims 1 to 3, wherein The main air hole and the sub-air hole have a hexagonal prism shape with an m-plane as the side surface.

7. The surface-emitting laser element according to any one of claims 1 to 3, wherein When the air hole filling rates of the main air hole and the sub-air hole in the photonic crystal layer are set as FF1 and FF2, the air hole filling rate ratio RF = FF1 / FF2 satisfies 1.7 ≤ RF ≤ 7.

5.

8. The surface-emitting laser element according to any one of claims 1 to 3, wherein The guiding layer is a GaN layer, The embedding layer has a first embedding layer that is a GaN layer and a second embedding layer formed on the first embedding layer and containing In (indium) in its composition.

9. A method for manufacturing a surface-emitting laser element composed of a group-III nitride semiconductor, the manufacturing method having: A step of forming a guiding layer on the c-plane of the group-III nitride semiconductor; The step of forming an etching mask on the guiding layer, the etching mask having an opening group including at least a main opening and a sub-opening smaller in size than the main opening at each square lattice point; The process of etching the guiding layer using the etching mask to form main holes and sub-holes; The process of performing crystal growth including mass transfer to form an embedding layer that closes the openings of the main holes and sub-holes, and to form a multi-lattice photonic crystal layer having a group of air holes arranged at each of the square lattice points, the group of air holes including a main air hole and a sub-air hole having an air hole diameter and depth smaller than those of the main air hole; and The process of forming a semiconductor layer including an active layer on the multi-lattice photonic crystal layer, The embedding and closing surfaces of the main air hole and the sub-air hole are on the side closer to the active layer in the photonic crystal layer, The main air hole has a regular hexagonal prism shape, a flat hexagonal prism shape, or an elliptical cylinder shape with its major axis parallel to the <11-20> axis.

10. The method for manufacturing a surface-emitting laser element according to claim 9, wherein, The sub-air hole has a regular hexagonal prism shape, a flat hexagonal prism shape, or an elliptical cylinder shape with its major axis parallel to the <11-20> axis.

11. A surface-emitting laser element composed of a group-III nitride semiconductor and having: A first guiding layer having a photonic crystal layer and an embedding layer, the photonic crystal layer being formed on the c-plane of the group-III nitride semiconductor and having air holes two-dimensionally and periodically arranged in a plane parallel to the layer, and the embedding layer being formed on the photonic crystal layer to close the air holes; An active layer formed on the first guiding layer; And A second guiding layer formed on the active layer, A group of air holes is arranged at each square lattice point in a plane parallel to the photonic crystal layer, the group of air holes including at least a main air hole and a sub-air hole smaller in size than the main air hole, The embedding and closing surfaces of the main air hole and the sub-air hole are on the side closer to the active layer in the photonic crystal layer, The main air hole and the sub-air hole have a regular hexagonal prism shape with their major axes parallel to the <11-20> axis.

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