Photonic crystal surface emitting laser

Abstract

A photonic crystal surface emitting laser includes: a first semiconductor layer; an active layer; a photonic crystal layer; a second semiconductor layer; a first electrode; a second electrode; and a dielectric film. The photonic crystal layer has a first region, and a plurality of second regions having a refractive index different from that of the first region. The first electrode has an opening. The second electrode overlaps the opening in the stacking direction. One of the central portion and the outer peripheral portion of the second electrode has a contact portion and a non-contact portion. At the contact portion, the second electrode is in contact with the second semiconductor layer. In the non-contact portion, a dielectric film is provided between the second electrode and the second semiconductor layer. The second electrode is in contact with the second semiconductor layer at the other of the central portion and the outer peripheral portion of the second electrode.

Description

Technical Field

[0001] This invention relates to photonic crystal surface-emitting lasers. Background Technology

[0002] Photonic-crystal surface-emitting lasers (PCSELs) are known to be formed by stacking a photonic crystal and an active layer with optical gain. Techniques for enabling PCSELs to operate in single mode are being researched (Non-Patent Document 1 and Non-Patent Document 2, etc.).

[0003] Existing technical documents Non-patent literature Non-patent literature 1: Ryohei Morita et.al. "Photonic-crystal lasers with two-dimensionally arranged gain and loss sections for high-peak-power short-pulse operation", NATURE PHOTONICS VOL.15, 311-318 (April 2021) Non-Patent Document 2: Miyai Eiji et al., "Current Distribution Control for Improving the Robustness of Single-Mode Operation of Photonic Crystal Lasers", Proceedings of the 83rd Autumn Academic Lecture of the Chinese Society of Applied Physics, 21a-A101-7 (2022). Summary of the Invention The problem the invention aims to solve However, there is a risk of increased threshold current and component resistance, as well as decreased efficiency. Therefore, the aim is to provide a photonic crystal surface-emitting laser capable of oscillating in a single mode.

[0004] means for solving problems The photonic crystal surface-emitting laser of the present invention comprises: a first semiconductor layer; an active layer disposed on one side of the first semiconductor layer; a photonic crystal layer stacked on the active layer; a second semiconductor layer disposed on the side of the active layer opposite to the first semiconductor layer; a first electrode disposed opposite to the active layer relative to the first semiconductor layer; a second electrode disposed on the side of the second semiconductor layer opposite to the active layer; and a dielectric film, wherein the photonic crystal layer has a first region and a plurality of second regions having a refractive index different from the first region, and the first electrode has an opening in the first semiconductor layer, the active layer, and the photonic crystal layer. In the direction in which the photonic crystal layer and the second semiconductor layer are stacked, the second electrode overlaps with the opening. One of the central portion and the outer peripheral portion of the second electrode has at least one contact portion and a non-contact portion. In the at least one contact portion, the second electrode is in contact with the second semiconductor layer. In the non-contact portion, the dielectric film is disposed between the second electrode and the second semiconductor layer, and the second electrode is separated from the second semiconductor layer. In the other of the central portion and the outer peripheral portion of the second electrode, the dielectric film is not disposed between the second electrode and the second semiconductor layer, and the second electrode is in contact with the second semiconductor layer.

[0005] Invention Effects According to the present invention, a photonic crystal surface laser capable of oscillating in a single mode can be provided. Attached Figure Description

[0006] Figure 1 This is a cross-sectional view illustrating the photonic crystal surface-emitting laser according to the first embodiment.

[0007] Figure 2A This is a magnified cross-sectional view of the photonic crystal layer.

[0008] Figure 2B This is a top view illustrating a photonic crystal layer.

[0009] Figure 3A This is a bottom view illustrating a surface-emitting laser from a photonic crystal.

[0010] Figure 3B This is a top view illustrating a surface-emitting laser from a photonic crystal.

[0011] Figure 4A This is a cross-sectional view illustrating the central portion of the electrode.

[0012] Figure 4B This is a top view illustrating the outer periphery of the electrode.

[0013] Figure 4C It is a sectional view illustrating the outer periphery.

[0014] Figure 5A This is a schematic diagram illustrating the distribution of light.

[0015] Figure 5B This is a schematic diagram illustrating the distribution of light.

[0016] Figure 6A This is a graph illustrating the threshold gain.

[0017] Figure 6B This is a diagram illustrating the threshold current.

[0018] Figure 7 This is a diagram illustrating the intensity of light.

[0019] Figure 8A This is a cross-sectional view illustrating a method for manufacturing a surface-emitting laser from a photonic crystal.

[0020] Figure 8B This is a cross-sectional view illustrating a method for manufacturing a surface-emitting laser from a photonic crystal.

[0021] Figure 8C This is a cross-sectional view illustrating a method for manufacturing a surface-emitting laser from a photonic crystal.

[0022] Figure 9 This is a top view illustrating the photonic crystal surface-emitting laser according to the second embodiment.

[0023] Figure 10A This is a cross-sectional view illustrating the central portion of the electrode.

[0024] Figure 10B This is a cross-sectional view illustrating the outer periphery of the electrode. Detailed Implementation

[0025] [Description of embodiments of the present invention] First, the embodiments of the present invention will be listed and described.

[0026] One aspect of the present invention is (1) a photonic crystal surface-emitting laser, the photonic crystal surface-emitting laser comprising: a first semiconductor layer; an active layer disposed on one side of the first semiconductor layer; a photonic crystal layer stacked on the active layer; a second semiconductor layer disposed on the side of the active layer opposite to the first semiconductor layer; a first electrode disposed opposite to the active layer relative to the first semiconductor layer; a second electrode disposed on the side of the second semiconductor layer opposite to the active layer; and a dielectric film, the photonic crystal layer having a first region and a plurality of second regions having a refractive index different from the first region, the first electrode having an opening in the first semiconductor layer. In the stacked direction of the body layer, the active layer, the photonic crystal layer, and the second semiconductor layer, the second electrode overlaps with the opening. One of the central portion and the outer peripheral portion of the second electrode has at least one contact portion and one non-contact portion. At the at least one contact portion, the second electrode contacts the second semiconductor layer. At the non-contact portion, a dielectric film is disposed between the second electrode and the second semiconductor layer, separating the second electrode from the second semiconductor layer. In the other of the central and outer peripheral portions of the second electrode, no dielectric film is disposed between the second electrode and the second semiconductor layer, and the second electrode contacts the second semiconductor layer. In a photonic crystal surface-emitting laser, the threshold gain of the central portion is lower than that of the outer peripheral portion. The fundamental mode oscillates easily, while higher-order modes are difficult to oscillate. A photonic crystal surface-emitting laser can oscillate in a single mode.

[0027] (2) In (1) above, the reflection phase in the central portion of the second electrode and the reflection phase in the outer peripheral portion can differ by more than π / 2 and less than 3π / 2. The gain difference between the central portion and the outer peripheral portion of the photonic crystal surface-emitting laser increases. Single-mode oscillation is possible.

[0028] (3) In (1) or (2) above, when the length of the second electrode is L, the width of the outer periphery of the second electrode may also be L / 4 or less. By increasing the gain difference, higher-order modes are suppressed, and oscillation with the fundamental mode is easier.

[0029] (4) In any of (1) to (3) above, the ratio of the area of ​​the at least one contact portion to the total area of ​​the at least one contact portion and the non-contact portion may be 5% or more and 30% or less. This can improve the threshold gain of the outer periphery of the photonic crystal surface-emitting laser. It can also suppress the increase in contact resistance.

[0030] (5) In any of (1) to (4) above, the at least one contact portion comprises a plurality of contact portions, which may also be arranged periodically. This enables the current to be nearly uniform.

[0031] (6) In any of (1) to (5) above, the planar shape of the second electrode may be circular, and the planar shape of the outer periphery of the second electrode may be annular. The threshold gain of the central portion of the photonic crystal surface-emitting laser is lower than that of the outer periphery, thereby enabling single-mode oscillation.

[0032] (7) In any of (1) to (6) above, the outer periphery of the second electrode may have at least one contact portion and the non-contact portion, and in the central portion of the second electrode, no dielectric film is disposed between the second electrode and the second semiconductor layer, and the second electrode is in contact with the second semiconductor layer. Single-mode oscillation is possible. Contact resistance is reduced.

[0033] (8) In any of (1) to (6) above, the central portion of the second electrode may have at least one contact portion and the non-contact portion, and the dielectric film is not disposed between the second electrode and the second semiconductor layer at the outer periphery of the second electrode, and the second electrode is in contact with the second semiconductor layer. Single-mode oscillation is possible.

[0034] (9) In (1) to (8) above, the second semiconductor layer may also include a cladding layer and a contact layer, with the cladding layer and the contact layer sequentially stacked between the active layer and the second electrode. A voltage can be applied to the first electrode and the second electrode to inject charge carriers into the active layer.

[0035] [Detailed description of the embodiments of the present invention] Specific examples of a photonic crystal surface-emitting laser according to embodiments of the present invention will be described below with reference to the accompanying drawings. Furthermore, the present invention is not limited to these examples, but is defined by the claims and is intended to include all modifications equivalent to and within the scope of the claims.

[0036] <First Implementation> (Photonic crystal surface-emitting laser) Figure 1 This is a cross-sectional view illustrating the photonic crystal surface-emitting laser 100 according to the first embodiment. Figure 1 As shown, the photonic crystal surface-emitting laser (PCSEL) 100 includes a substrate 10, a cladding layer 12 (first semiconductor layer), a photonic crystal layer 14, a cladding layer 16, an active layer 18, a cladding layer 20 (second semiconductor layer), a contact layer 22 (second semiconductor layer), an electrode 24 (first electrode), and an electrode 26 (second electrode). Figure 1 Not shown in the figure, but the photonic crystal surface-emitting laser 100 has a dielectric film 50.

[0037] The semiconductor layers are stacked along the Z-axis. Above the substrate 10, a cladding layer 12, a photonic crystal layer 14, a cladding layer 16, an active layer 18, a cladding layer 20, and a contact layer 22 are stacked sequentially. The surfaces of each layer are parallel to the XY plane. The X-axis, Y-axis, and Z-axis are orthogonal to each other. Electrode 24 is electrically connected to the substrate 10. Electrode 26 is electrically connected to the contact layer 22.

[0038] The substrate 10, cladding layer 12, and cladding layer 16 are formed, for example, of n-type indium phosphide (n-InP). The n-type dopant is, for example, silicon (Si). The thickness of cladding layer 12 is, for example, 500 nm. The thickness of cladding layer 16 is, for example, 100 nm.

[0039] The photonic crystal layer 14 is formed, for example, of n-type indium gallium arsenide phosphide (InGaAsP) or aluminum indium gallium arsenide (AlInGaAs). The thickness of the photonic crystal layer 14 is, for example, 300 nm.

[0040] The active layer 18 comprises multiple well layers and a barrier layer, exhibiting a multi-quantum-well (MQW) structure. The well layers and barrier layers are formed, for example, from undoped indium gallium arsenide phosphide (InGaAsP) or indium aluminum gallium arsenide (AlGaInAs). These materials are examples; the layers can be formed from other materials, or a combination of the aforementioned materials with other materials can be used.

[0041] The cladding layer 20 is formed, for example, of p-type indium phosphide (p-InP) with a thickness of 3 μm. The contact layer 22 is formed, for example, of p-type indium gallium arsenide (p-InGaAs) with a thickness of 300 nm. The p-type dopant is, for example, zinc (Zn).

[0042] The refractive index of the active layer 18 is, for example, 3.5. The refractive index of the InP cladding layer is, for example, 3.2. The refractive index of InGaAsP, which serves as the parent material of the photonic crystal layer 14, is higher than that of the cladding layer, for example, 3.4.

[0043] Figure 2A This is a magnified cross-sectional view of photonic crystal layer 14. Figure 2B This is a top view illustrating the photonic crystal layer 14. The photonic crystal layer 14 has a substrate 30 (first region), vias 32 (second region), and vias 34 (second region). The substrate 30, as described above, is an InGaAsP layer or the like. Multiple vias 32 and multiple vias 34 are provided in the substrate 30.

[0044] like Figure 2AAs shown, holes 32 and 34 extend along the Z-axis. One end of each of holes 32 and 34 is located on one face of the photonic crystal layer 14. The other end of each of holes 32 and 34 is located midway through the photonic crystal layer 14. Holes 32 and 34 may also extend into the cladding layer 12, for example. Hole 32 is longer than hole 34. The interior of holes 32 and 34 is air. The refractive index of holes 32 and 34 differs from that of the parent material 30. Within the face of the photonic crystal layer 14, the refractive index changes periodically.

[0045] like Figure 2B As shown, multiple holes 32 are arranged in a square lattice pattern. Multiple holes 34 are also arranged in a square lattice pattern. The multiple holes 32 are arranged periodically in the X-axis and Y-axis directions. The lattice constant of the square lattice is 400 nm. That is, the distance between adjacent holes 32 and the distance between adjacent holes 34 are 400 nm. The multiple holes 34 are arranged circumferentially. The planar shape of the holes 32 is elliptical. The major and minor axes of the holes 32 are inclined from the direction in which the multiple holes 32 are arranged. The planar shape of the holes 34 is circular.

[0046] Figure 3A This is a bottom view illustrating a photonic crystal surface-emitting laser 100. (Example) Figure 3A As shown, an opening 25 is provided on electrode 24. The planar shape of opening 25 is circular. The diameter D1 of opening 25 is, for example, 340 μm. Opening 25 extends through electrode 24. Substrate 10 is exposed from opening 25. Opening 25 functions as an opening for emitting light. The lengths L1 and L2 of one side of photonic crystal surface-emitting laser 100 are, for example, 1000 μm.

[0047] Electrode 24 is an n-type electrode that is in surface contact with substrate 10. Electrode 24 is formed of metal, for example, by stacking nickel (Ni), germanium (Ge), and gold (Au) from a portion close to substrate 10.

[0048] Figure 3B This is a top view illustrating a photonic crystal surface-emitting laser 100. The planar shape of electrode 26 is circular. Electrode 26 is a p-type electrode, formed, for example, by stacking titanium (Ti), platinum (Pt), and gold (Au) near the contact layer 22. The center of electrode 26 in the XY plane is designated C.

[0049] Electrode 26 has a central portion 40 and an outer peripheral portion 42. The central portion 40 is located in the center of electrode 26. The outer peripheral portion 42 is... Figure 3BThe portion marked with a diagonal line is located outside the central portion 40, surrounding it. The planar shape of the central portion 40 is circular. The planar shape of the outer peripheral portion 42 is annular. The diameter L of the electrode 26 is, for example, 200 μm or more and 300 μm or less. The width W of the outer peripheral portion 42 is, for example, about 10% of the diameter L, and can be 20 μm or more and 30 μm or less. The diameter D2 of the central portion 40 is equal to L-2W.

[0050] Figure 4A This is a cross-sectional view illustrating the central portion 40 of electrode 26, showing the range from the coating layer 20 to electrode 26. (See attached image.) Figure 4A As shown, the central portion 40 of electrode 26 is a solid structure. No dielectric film 50 is disposed between electrode 26 and contact layer 22 in the central portion 40. The entire surface 26a of electrode 26 is in contact with contact layer 22.

[0051] Figure 4B This is a top view illustrating the outer periphery 42 of electrode 26. (Example) Figure 4B As shown, the outer peripheral portion 42 has a mesh structure, with contact portions 44 and non-contact portions 46. The mesh structure refers to the arrangement of multiple contact portions 44. The non-contact portions 46 are located around the contact portions 44.

[0052] The planar shape of the contact portion 44 is rectangular. The length L3 of one side of the contact portion 44 is, for example, 1.6 μm. Multiple contacts 44 can be arranged periodically or randomly. Figure 4B In the example, multiple contact portions 44 are periodically arranged in the X-axis and Y-axis directions. The distance (spacing) L4 between the corresponding edges of adjacent contact portions 44 is, for example, 5.0 μm. The area adequacy (Filling Factor: FF) of the contact portions 44 is calculated by the following formula (1), for example, more than 5% and less than 30%.

[0053] FF = (L3) 2 / (L4) 2 (1) Figure 4C This is a sectional view illustrating the outer periphery 42, along... Figure 4B The cross-section of line AA is illustrated. For example... Figure 4C As shown, a dielectric film 50 is disposed between the electrode 26 and the contact layer 22 in the outer peripheral portion 42. The dielectric film 50 is formed of an insulator such as silicon nitride (SiN). Let the thickness of the dielectric film 50 be T1.

[0054] In the contact portion 44, an opening 52 is provided in the dielectric film 50. The opening 52 extends through the dielectric film 50 along the Z-axis. An electrode 26 is disposed within the opening 52. The surface 26b of the electrode 26 is in contact with the contact layer 22. In the non-contact portion 46, no opening 52 is provided in the dielectric film 50. The electrode 26 in the non-contact portion 46 is disposed on the upper surface of the dielectric film 50 and is not in contact with the contact layer 22. The surface 26c of the electrode 26 is in contact with the dielectric film 50.

[0055] The operation of the photonic crystal surface-emitting laser 100 will be explained. A voltage is applied to the photonic crystal surface-emitting laser 100 through electrodes 24 and 26. Carriers are injected into the active layer 18, generating light. The light is diffracted within the plane of the photonic crystal layer 14. A resonator is formed between electrode 26 and photonic crystal layer 14. Electrode 26 functions as one mirror of the resonator of the photonic crystal surface-emitting laser 100. Photonic crystal layer 14 functions as the other mirror of the resonator of the photonic crystal surface-emitting laser 100. The light resonates between electrode 26 and photonic crystal layer 14. The light, having wavelengths corresponding to the periods of apertures 32 and 34, is amplified, causing laser oscillation. The laser wavelengths are in the 1.3 μm band and the 1.55 μm band, etc.

[0056] The laser beam is emitted along the Z-axis. Figure 1 Light propagating downwards is emitted from the opening 25 of electrode 24. Light propagating upwards is reflected by the lower surface of electrode 26, propagates downwards, and is emitted from the opening 25.

[0057] Figure 5A as well as Figure 5B This is a schematic diagram illustrating the distribution of light. Figure 5A Represents the fundamental mode. Figure 5B Representing higher-order modes. Light is illustrated with dashed lines. For example... Figure 5A as well as Figure 5B As shown, the fundamental mode and higher-order modes are generated. Figure 5A As shown, the fundamental mode is strongly distributed in the central part 40. (As indicated...) Figure 5B As shown, the higher-order mode extends outward to the outer periphery 42.

[0058] To achieve single-mode laser oscillation, the fundamental mode oscillates while suppressing the oscillation of higher-order modes. By reducing the threshold gain of the resonator at the lower part of the central portion 40, the fundamental mode becomes easier to oscillate. By making the threshold gain of the lower part of the outer peripheral portion 42 higher than that of the lower part of the central portion 40, higher-order modes become more difficult to oscillate. Figure 3B As shown, the central part 40 is a solid structure and the outer peripheral part 42 is a mesh structure, thereby enabling the threshold gain to be changed between the central part 40 and the outer peripheral part 42.

[0059] The threshold gain gth is expressed by the following equation (2).

[0060] gth=(1+(√R)cosθ)α1+α2+α3 (2) R is the reflectivity of light relative to electrode 26. α1 is the emissivity of the oscillation band. α2 is the in-plane loss. α3 is the internal loss. θ is the phase difference (reflection phase) between the emitted light from photonic crystal layer 14 towards electrode 26 and the reflected light reflected by electrode 26.

[0061] like Figure 4A As shown, in the central portion 40, the surface 26a of the electrode 26 contacts the contact layer 22. Light that has passed through the contact layer 22 is reflected by the surface 26a. Figure 4C As shown, in the outer peripheral portion 42, the electrode 26 has a surface 26b and a surface 26c. Surface 26b is in contact with the contact layer 22. Light transmitted through the contact layer 22 is reflected by surface 26b. Surface 26c is disposed on the dielectric film 50. Light transmitted through the contact layer 22 and the dielectric film 50 is reflected by surface 26c.

[0062] Due to the influence of the thickness and refractive index of the dielectric film 50, the optical path length in the non-contact portion 46 is different from that in the contact portion 44 and the central portion 40. The phase of the reflected light changes due to the change in optical path length, and the phase difference θ also changes. This allows the threshold gain gth of the resonator at the lower part of the central portion 40 to be different from the threshold gain gth of the resonator at the lower part of the outer peripheral portion 42.

[0063] Figure 6A This is a graph illustrating the threshold gain. The horizontal axis represents the reflection phase. The vertical axis represents the threshold gain. The threshold gain gth is calculated using equation (2) above. Corresponding to the reflection phase θ, the threshold gain gth varies periodically. The threshold gain gth has a minimum value when the reflection phase θ is π and 3π. The threshold gain gth has a maximum value when the reflection phase θ is 0 and 2π. The minimum value is approximately 16 cm. -1 The maximum value is approximately 33 cm. -1 .

[0064] Figure 6B This diagram illustrates the threshold current. The horizontal axis represents the thickness of the dielectric film 50. The right vertical axis and the circle represent the reflection phase. The left vertical axis represents the threshold current. The triangle represents the threshold current of the mesh structure. The dashed line represents the threshold current of the solid structure. The thickness T1 of the dielectric film 50 is varied from 0 nm to 600 nm to simulate the reflection phase and threshold current. When T1 = 0 nm, no dielectric film 50 is provided between the contact layer 22 and the electrode 26, corresponding to the central portion 40 of the solid structure. When T1 is finite, a dielectric film 50 is provided between the contact layer 22 and the electrode 26, corresponding to the outer periphery 42 of the mesh structure.

[0065] Corresponding to the thickness T1, the threshold current Ith and the reflection phase θ change periodically. For example... Figure 6B The dashed line indicates that when T1 = 0 nm, the threshold current is approximately 180 mA. With a thickness T1 of approximately 250 nm, the reflection phase is π, and the threshold current Ith represents its maximum value. With thicknesses around 0 nm and approximately 400 nm, the reflection phase is close to 0, and the threshold current Ith represents its minimum value. The maximum value of the threshold current Ith is approximately 300 mA, and the minimum value is approximately 170 mA.

[0066] Figure 7 This is a diagram illustrating the intensity of light. The horizontal axis represents the position within the plane of the photonic crystal surface-emitting laser 100. 0 on the horizontal axis represents the center C of the photonic crystal surface-emitting laser 100. The diameter L of the electrode 26 is 200 μm. The width of the outer periphery 42 is 30 μm. The outer periphery 42 extends from -70 μm to -100 μm and from 70 μm to 100 μm. The central portion 40 extends from -70 μm to 70 μm. The thickness of the dielectric film 50 is 200 nm. The vertical axis represents the intensity of light, which is normalized. Solid lines represent the fundamental mode. Dashed lines represent higher-order modes of the first order. The intensity of the fundamental mode is maximum at 0 (center) and decreases further away from the center. The intensity of higher-order modes is maximum at 50 nm and -50 nm, and minimum at 0 and ±100 nm.

[0067] The threshold gain gth of the resonator in the lower part of the central section 40 is 28cm. -1 The threshold gain gth of the resonator at the lower part of the outer periphery 42 is set to 49cm. -1 Corresponding to the light intensities of the fundamental mode and higher-order modes, the threshold gain is calculated by weighted averaging of the threshold gains. The threshold gain of the higher-order modes is 33.6 cm⁻¹. -1 The threshold gain of the fundamental mode is lower than that of the higher-order modes, at 31 cm⁻¹. -1 The fundamental mode is prone to oscillation, which can suppress the oscillation of higher-order modes.

[0068] (Manufacturing method) Figures 8A to 8C This is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser 100. (Example) Figure 8A As shown, for example, a cladding layer 12 and a photonic crystal layer 14 are epitaxially grown sequentially on a substrate 10 using metal-organic chemical vapor deposition (MOCVD). In this process, the substrate 30 (InGaAsP) used to form the photonic crystal layer 14 does not form voids.

[0069] A mask (not shown) is disposed on the upper surface of the photonic crystal layer 14. The mask is formed of an insulator such as SiN. An insulating film is formed on the upper surface of the photonic crystal layer 14. A resist pattern is formed by an electron beam (EB) or similar method, and the resist pattern is transferred onto the insulating film, thereby forming the mask. The upper surface of the substrate 30 is exposed through the opening of the mask. Holes 32 and 34 are formed in the photonic crystal layer 14 by reactive ion etching (RIE) or similar methods. The etching proceeds, for example, to the middle of the photonic crystal layer 14, but not to the lower surface of the photonic crystal layer 14. The planar shape of the holes 32 and 34 is determined by the planar shape of the opening of the mask. For example, as shown... Figure 2B As shown, elliptical holes 32 and circular holes 34 are formed. After etching, the mask is removed.

[0070] like Figure 8B As shown, a cladding layer 16, an active layer 18, a cladding layer 20, and a contact layer 22 are epitaxially grown above the photonic crystal layer 14. Holes 32 and 34 are sealed by the cladding layer 16. The inner side of the holes is not filled by the cladding layer 16 and remains empty. The active layer 18, the cladding layer 20, and the contact layer 22 are epitaxially grown above the flat cladding layer 16.

[0071] exist Figure 8C In this diagram, the region from the active layer 18 to the substrate 10 is omitted; the region above the active layer 18 is shown, corresponding to the outer peripheral portion 42. In the outer peripheral portion 42, a dielectric film 50 is formed on the upper surface of the contact layer 22, for example, by plasma-enhanced CVD (PECVD). Multiple openings 52 are formed in the dielectric film 50 by etching or the like. In the central portion 40, the contact layer 22 is exposed.

[0072] Electrode 26 is formed by vapor deposition and removal. For example, a Ti layer, a Pt layer, and an Au layer are stacked sequentially. Electrode 26 is in contact with the upper surface of contact layer 22 at the central portion 40. Electrode 26 is disposed on the upper surface of dielectric film 50 at the outer peripheral portion 42 and is in contact with the upper surface of contact layer 22 inside the opening 52. On the lower surface of substrate 10, such as... Figure 1 Electrode 24 is provided, forming an opening 25. For example, heat treatment at a temperature of 300°C or higher is performed to achieve contact between the electrode and the semiconductor. Through the above process, a photonic crystal surface-emitting laser 100 is formed.

[0073] According to the first embodiment, the central portion 40 of the electrode 26 has a solid structure and contacts the contact layer 22. The outer peripheral portion 42 has a mesh structure, including a contact portion 44 and a non-contact portion 46. In the contact portion 44, the electrode 26 contacts the contact layer 22. In the non-contact portion 46, a dielectric film 50 is disposed between the electrode 26 and the contact layer 22. The electrode 26 is disposed on the dielectric film 50 and does not contact the contact layer 22. The threshold gain of the resonator at the lower part of the central portion 40 is lower than the threshold gain of the resonator at the lower part of the outer peripheral portion 42. Since the fundamental mode is strongly distributed in the central portion 40 where the threshold gain is low, it is easy to oscillate. Since the higher-order modes extend to the outer peripheral portion 42 where the threshold gain is high, it is difficult to oscillate. The higher-order modes are cut off, so the photonic crystal surface-emitting laser 100 can oscillate in a single mode.

[0074] The thickness T1 of the dielectric film 50 determines the reflection phase θ, threshold gain gth, and threshold current Ith. The threshold gain gth and threshold current Ith are determined by the thickness T1 in a manner that is low in the central portion 40 and increases in the outer peripheral portion 42. The threshold gain gth and threshold current Ith of the resonator in the lower part of the central portion 40 are lower than those in the outer peripheral portion 42, making the fundamental mode prone to oscillation and cutting off higher-order modes. Single-mode oscillation is possible.

[0075] like Figure 6A as well as Figure 6B As shown, due to the phase difference, the difference between the threshold gain and the threshold current increases between the central portion 40 and the outer peripheral portion 42. For example, the reflection phase in the central portion 40 and the reflection phase in the outer peripheral portion 42 can differ by more than π / 2 and less than 3π / 2, more preferably by π. The threshold gain of the resonator at the lower part of the central portion 40 is close to a minimum, while the threshold gain of the resonator at the lower part of the outer peripheral portion 42 is close to a maximum. Therefore, the gain difference increases between the central portion 40 and the outer peripheral portion 42. Oscillation in the fundamental mode is possible.

[0076] For example, the thickness T1 of the dielectric film 50 is 200 nm. Figure 6B As shown, the phase difference of the reflection between the central portion 40 of the solid structure and the outer peripheral portion 42 of the mesh structure is close to π. The threshold current of the resonator at the lower part of the outer peripheral portion 42 is high, while the threshold current of the resonator at the lower part of the central portion 40 is low. The threshold gain of the fundamental mode is 31cm. -1 The threshold gain of the higher-order modes is 33.6 cm⁻¹. -1 The gain difference between the fundamental mode and higher-order modes is 2.6 cm. -1 It can suppress higher-order modes.

[0077] like Figure 3AAs shown, the central portion 40 is a solid structure. No dielectric film 50 is disposed between the electrode 26 and the contact layer 22. The entire surface 26a of the electrode 26 is in contact with the contact layer 22. Due to the low contact resistance, current can be injected effectively, resulting in higher efficiency.

[0078] like Figure 3B As shown, the outer peripheral portion 42 surrounds the central portion 40. If the width of the outer peripheral portion 42 is W, and the diameter (length) of the electrode 26 is L, then the width W can be, for example, less than L / 4, less than L / 3, or less than L / 5. If the outer peripheral portion 42 is wide, the difference between the threshold gain of the fundamental mode and the threshold gain of higher-order modes becomes smaller. By making the width W L / 4, the outer peripheral portion 42 becomes narrower, which increases the difference between the threshold gain of the fundamental mode and the threshold gain of higher-order modes. The fundamental mode becomes more prone to oscillation. If the outer peripheral portion 42 is too narrow, since higher-order modes are also distributed in the central portion 40, higher-order modes become more prone to oscillation. The width W can also be greater than L / 10 or greater than L / 20. Higher-order modes can be suppressed.

[0079] The outer peripheral portion 42 has a contact portion 44 and a non-contact portion 46. If the proportion of the contact portion 44 in the outer peripheral portion 42 is large, the gain difference between the outer peripheral portion 42 and the central portion 40 becomes smaller. If the proportion of the contact portion 44 is small, the contact resistance increases. The proportion of the area of ​​the contact portion 44 in the outer peripheral portion 42 is, for example, 5% or more and 30% or less, or 10% or more and 20% or less. This can improve the threshold gain of the resonator in the lower part of the outer peripheral portion 42 and suppress the increase in contact resistance.

[0080] like Figure 4B As shown, multiple contacts 44 are arranged periodically. This allows the current injected into the active layer 18 to be nearly uniform. The multiple contacts 44 can also be arranged non-periodically. The planar shape of the contacts 44 can be rectangular, circular, elliptical, or polygonal.

[0081] like Figure 3B As shown, the planar shape of electrode 26 is circular. The planar shape of the central portion 40 is circular. The planar shape of the outer peripheral portion 42 is annular. The fundamental mode is circular and distributed in the central portion 40 where the threshold is low. The fundamental mode is prone to oscillation. The planar shapes of electrode 26 and the central portion 40 can also be elliptical or polygonal. The planar shape of the outer peripheral portion 42 is annular or can be an elliptical arc, etc.

[0082] Substrate 10, cladding layer 12, photonic crystal layer 14, and cladding layer 16 have n-type conductivity. Active layer 18 is an undoped layer. Cladding layer 20 and contact layer 22 have p-type conductivity. These layers are stacked to form a pin junction (positive-intrinsic-negative). Electrode 26 is disposed above the p-type contact layer 22. Applying a voltage to electrodes 24 and 26 allows carrier injection into active layer 18. Alternatively, the conductivity can be reversed. An n-type layer can be disposed on one side of active layer 18, and a p-type layer on the opposite side.

[0083] The photonic crystal layer 14 can have two types of voids, but it can also have one type or more than three types. The planar shape of the voids can also be elliptical, circular, or polygonal. Regions with a refractive index different from the parent material 30 are periodically provided in the photonic crystal layer 14. These regions can be voids or components different from the parent material 30. The photonic crystal layer 14 can be disposed between the cladding layer 12 and the active layer 18, or between the active layer 18 and the cladding layer 20.

[0084] <Second Implementation> Figure 9 This is a top view illustrating the photonic crystal surface-emitting laser 200 according to the second embodiment. Figure 10A This is a cross-sectional view illustrating the central portion 40 of electrode 26. Figure 10B This is a cross-sectional view illustrating the outer periphery 42 of electrode 26. The central portion 40 has a mesh structure. The outer periphery 42 has a solid structure. Descriptions of configurations identical to those in the first embodiment are omitted.

[0085] According to the second embodiment, the outer peripheral portion 42 of the electrode 26 has a solid structure. The central portion 40 has a mesh structure, including a contact portion 44 and a non-contact portion 46. In the non-contact portion 46, a dielectric film 50 is disposed between the electrode 26 and the contact layer 22. By adjusting the thickness of the dielectric film 50, the threshold gain of the resonator at the lower part of the central portion 40 is lower than the threshold gain of the resonator at the lower part of the outer peripheral portion 42. The fundamental mode oscillates easily, while higher-order modes are difficult to oscillate. Higher-order modes are cut off, and the photonic crystal surface-emitting laser 200 can oscillate in a single mode.

[0086] The reflection phase in the central portion 40 and the reflection phase in the outer peripheral portion 42 can differ by more than π / 2 and less than 3π / 2, more preferably by π. Due to this phase difference, a difference exists between the threshold gain and the threshold current between the central portion 40 and the outer peripheral portion 42. The threshold gain of the resonator at the lower part of the central portion 40 is close to a minimum, while the threshold gain of the resonator at the lower part of the outer peripheral portion 42 is close to a maximum, thereby effectively cutting off higher-order modes. Oscillation in the fundamental mode is possible.

[0087] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments described above, and various modifications and alterations can be made within the scope of the spirit of the present invention as set forth in the claims.

Claims

1. A photonic crystal surface-emitting laser, characterized in that, The photonic crystal surface-emitting laser has the following features: First semiconductor layer; An active layer is disposed on one side of the first semiconductor layer; A photonic crystal layer is stacked on the active layer; The second semiconductor layer is disposed on the side of the active layer opposite to the first semiconductor layer; The first electrode is configured opposite to the active layer relative to the first semiconductor layer; The second electrode is disposed on the side of the second semiconductor layer opposite to the active layer; as well as Dielectric film, The photonic crystal layer has a first region and a plurality of second regions having a refractive index different from that of the first region. The first electrode has an opening. In the direction in which the first semiconductor layer, the active layer, the photonic crystal layer, and the second semiconductor layer are stacked, the second electrode overlaps with the opening. The second electrode has at least one contact portion and one non-contact portion, either in its central portion or its outer peripheral portion. In at least one contact portion, the second electrode is in contact with the second semiconductor layer. In the non-contact portion, a dielectric film is disposed between the second electrode and the second semiconductor layer, wherein the second electrode is separated from the second semiconductor layer. On the other side of the central portion and the outer periphery of the second electrode, there is no dielectric film between the second electrode and the second semiconductor layer, and the second electrode is in contact with the second semiconductor layer.

2. The photonic crystal surface-emitting laser according to claim 1, characterized in that, The reflection phase in the central portion of the second electrode differs from the reflection phase in the outer peripheral portion by more than π / 2 and less than 3π / 2.

3. The photonic crystal surface-emitting laser according to claim 1 or 2, characterized in that, With the length of the second electrode being L, The width of the outer periphery of the second electrode is less than L / 4.

4. The photonic crystal surface-emitting laser according to claim 1 or 2, characterized in that, The area of ​​the at least one contact portion is 5% to 30% of the total area of ​​the at least one contact portion and the non-contact portion.

5. The photonic crystal surface-emitting laser according to claim 1 or 2, characterized in that, The at least one contact portion includes a plurality of contact portions. The plurality of contact portions are periodically arranged.

6. The photonic crystal surface-emitting laser according to claim 1 or 2, characterized in that, The second electrode has a circular planar shape. The outer periphery of the second electrode has a circular shape.

7. The photonic crystal surface-emitting laser according to claim 1 or 2, characterized in that, The outer peripheral portion of the second electrode has at least one contact portion and the non-contact portion. In the central portion of the second electrode, no dielectric film is disposed between the second electrode and the second semiconductor layer, and the second electrode is in contact with the second semiconductor layer.

8. The photonic crystal surface-emitting laser according to claim 1 or 2, characterized in that, The central portion of the second electrode has at least one contact portion and the non-contact portion. In the outer periphery of the second electrode, no dielectric film is disposed between the second electrode and the second semiconductor layer, and the second electrode is in contact with the second semiconductor layer.

9. The photonic crystal surface-emitting laser according to claim 1 or 2, characterized in that, The second semiconductor layer includes a cladding layer and a contact layer. The coating layer and the contact layer are sequentially stacked between the active layer and the second electrode.

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