Photonic crystal surface emitting laser and manufacturing method thereof

Abstract

The invention provides a photonic crystal surface emitting laser capable of improving light output and a manufacturing method thereof. A photonic crystal surface emitting laser includes: a first semiconductor layer; the active layer is stacked on the first semiconductor layer; a second semiconductor layer provided opposite to the first semiconductor layer with respect to the active layer; the photonic crystal layer is arranged between the first semiconductor layer and the second semiconductor layer; a first electrode electrically connected to the first semiconductor layer; an insulating film provided on a surface of the second semiconductor layer opposite to the active layer; and a second electrode provided on a surface of the insulating film opposite to the second semiconductor layer, the photonic crystal layer having a first region and a plurality of second regions having a refractive index different from that of the first region, the insulating film having a plurality of openings, and the first region and the second region having a refractive index different from that of the first region. The second electrode is electrically connected with the second semiconductor layer.

Description

Technical Field

[0001] This disclosure relates to a photonic crystal surface-emitting laser and a method for manufacturing the same. 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 (Patent Document 1, etc.).

[0003] Existing technical documents Patent documents Patent Document 1: International Publication No. 2016 / 031966 Summary of the Invention The problem that the invention aims to solve Electrodes are disposed on the surface of a semiconductor layer. Light can be extracted by reflecting light generated in the active layer using the electrodes. However, the output is reduced because the light is scattered. Therefore, the objective is to provide a photonic crystal surface-emitting laser capable of improving light output and a method for manufacturing the same.

[0004] means for solving problems The photonic crystal surface-emitting laser disclosed herein comprises: a first semiconductor layer; an active layer stacked on the first semiconductor layer; a second semiconductor layer configured opposite to the first semiconductor layer relative to the active layer; a photonic crystal layer disposed between the first semiconductor layer and the second semiconductor layer; a first electrode electrically connected to the first semiconductor layer; an insulating film disposed on the side of the second semiconductor layer opposite to the active layer; and a second electrode disposed on the side of the insulating film opposite to the second semiconductor layer. The photonic crystal layer has a first region and a plurality of second regions having a refractive index different from the first region. The insulating film has a plurality of openings, in which the second electrode is electrically connected to the second semiconductor layer.

[0005] Invention Effects According to this disclosure, a photonic crystal surface-emitting laser capable of improving light output and a method for manufacturing the same can be provided. Attached Figure Description

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

[0007] Figure 2A This is a top view illustrating a photonic crystal layer.

[0008] Figure 2B This is a magnified top view of a region of the photonic crystal layer.

[0009] Figure 2C This is an enlarged cross-sectional view of the photonic crystal layer.

[0010] Figure 3A This is a bottom view illustrating an example of a photonic crystal surface-emitting laser.

[0011] Figure 3B This is a top view illustrating a photonic crystal surface-emitting laser.

[0012] Figure 4 This is a graph illustrating slope efficiency.

[0013] Figure 5A This is a cross-sectional view illustrating an example of a method for manufacturing a surface-emitting laser from a photonic crystal.

[0014] Figure 5B This is a cross-sectional view illustrating an example of a method for manufacturing a surface-emitting laser from a photonic crystal.

[0015] Figure 5C This is a cross-sectional view illustrating an example of a method for manufacturing a surface-emitting laser from a photonic crystal.

[0016] Figure 6A This is a cross-sectional view illustrating an example of a method for manufacturing a surface-emitting laser from a photonic crystal.

[0017] Figure 6B This is a cross-sectional view illustrating an example of a method for manufacturing a surface-emitting laser from a photonic crystal.

[0018] Figure 6C This is a cross-sectional view illustrating an example of a method for manufacturing a surface-emitting laser from a photonic crystal.

[0019] Figure 7A This is a cross-sectional view illustrating an example of a method for manufacturing a surface-emitting laser from a photonic crystal.

[0020] Figure 7B This is a cross-sectional view illustrating an example of a method for manufacturing a surface-emitting laser from a photonic crystal.

[0021] Figure 8 This is a cross-sectional view illustrating a photonic crystal surface-emitting laser according to the second embodiment.

[0022] Figure 9 This is a diagram illustrating light output as an example.

[0023] Figure 10 This is a graph showing the calculated results of reflectivity.

[0024] Figure 11A This is a graph representing slope efficiency.

[0025] Figure 11BThis is a graph representing slope efficiency.

[0026] Figure 11C This is a graph representing slope efficiency.

[0027] Figure 12A This is a cross-sectional view illustrating an example of a method for manufacturing a surface-emitting laser from a photonic crystal.

[0028] Figure 12B This is a cross-sectional view illustrating an example of a method for manufacturing a surface-emitting laser from a photonic crystal.

[0029] Figure 13A This is a top view illustrating a photonic crystal surface-emitting laser according to the third embodiment.

[0030] Figure 13B This is a top view illustrating the photonic crystal surface-emitting laser according to the fourth embodiment. Detailed Implementation

[0031] [Description of embodiments of this disclosure] First, the contents of the embodiments disclosed herein will be listed and explained.

[0032] One aspect of this disclosure is (1) a photonic crystal surface-emitting laser comprising: a first semiconductor layer; an active layer stacked on the first semiconductor layer; a second semiconductor layer configured opposite to the first semiconductor layer relative to the active layer; a photonic crystal layer disposed between the first semiconductor layer and the second semiconductor layer; a first electrode electrically connected to the first semiconductor layer; an insulating film disposed on the side of the second semiconductor layer opposite to the active layer; and a second electrode disposed on the side of the insulating film opposite to the second semiconductor layer, 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 insulating film has a plurality of openings in which the second electrode is electrically connected to the second semiconductor layer. Because an insulating film is disposed between the second electrode and the second semiconductor layer, the contact area between the second electrode and the second semiconductor layer is reduced. The lower surface of the second electrode is less prone to roughening, resulting in higher reflectivity. The phase of the light is adjusted by the thickness of the insulating film. This improves light output.

[0033] (2) Based on (1) above, the plurality of openings may also be periodically arranged within the surface of the insulating film, enabling uniform current injection.

[0034] (3) Based on (1) or (2) above, the area fill rate of the plurality of openings relative to the region where the second semiconductor layer is disposed may be 5% or more and 50% or less. This can suppress contact resistance and improve reflectivity.

[0035] (4) Based on any one of (1) to (3) above, the planar shape of the opening may also be rectangular, and the length of the opening may be more than 1 μm and less than 10 μm. This allows for easy fabrication of the opening. It also allows for near-uniform current distribution.

[0036] (5) Based on any one of (1) to (4) above, the second electrode may also include a first metal layer and a second metal layer, wherein the reflectivity of the second metal layer is higher than that of the first metal layer, the first metal layer is disposed at the plurality of openings of the insulating film, and the second metal layer is disposed on the surface of the insulating film. By increasing the reflectivity, the light output can be improved.

[0037] (6) Based on any one of (1) to (5) above, a third semiconductor layer may also be provided, which is disposed between the active layer and the second semiconductor layer, wherein the first semiconductor layer has an n-type conductivity, and the second and third semiconductor layers have a p-type conductivity. A pin junction is formed. The second electrode is connected to the second semiconductor layer through the opening. Carriers can be injected into the active layer.

[0038] (7) A method for manufacturing a photonic crystal surface-emitting laser, comprising: a step of stacking an active layer on a first semiconductor layer; a step of forming a photonic crystal layer; a step of forming a second semiconductor layer opposite to the first semiconductor layer relative to the active layer; a step of forming a first electrode electrically connected to the first semiconductor layer; a step of forming an insulating film on the side of the second semiconductor layer opposite to the active layer; a step of forming a plurality of openings in the insulating film; and a step of forming a second electrode on the side of the insulating film opposite to the second semiconductor layer, 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 second electrode is electrically connected to the second semiconductor layer in the plurality of openings. Because an insulating film is provided between the second electrode and the second semiconductor layer, the contact area between the second electrode and the second semiconductor layer is reduced. The lower surface of the second electrode is less prone to roughening, and the reflectivity is increased. The phase of the light is adjusted by the thickness of the insulating film. Light output can be improved.

[0039] (8) Based on (7) above, it is also possible to have a step of stacking a third semiconductor layer on the active layer, with the second semiconductor layer stacked on the third semiconductor layer, and in the step of forming the insulating film, to form an insulating film having a thickness based on the thickness from the active layer to the second semiconductor layer. By controlling the thickness of the insulating film, the phase of the light can be adjusted and the light output can be improved.

[0040] [Details of the embodiments disclosed herein] Hereinafter, specific examples of a photonic crystal surface-emitting laser and its manufacturing method according to embodiments of the present disclosure will be described with reference to the accompanying drawings. Furthermore, the present disclosure 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.

[0041] <First Implementation> (Photonic crystal surface-emitting laser) Figure 1 This is a cross-sectional view illustrating, by way of example, 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 (third semiconductor layer), a semiconductor layer 21, a contact layer 22 (second semiconductor layer), an electrode 24 (first electrode), and an electrode 26 (second electrode). The surfaces of each layer are parallel to the XY plane. The X-axis, Y-axis, and Z-axis are orthogonal to each other.

[0042] Semiconductor layers are stacked along the Z-axis. On substrate 10, cladding layer 12, photonic crystal layer 14, cladding layer 16, active layer 18, cladding layer 20, semiconductor layer 21, and contact layer 22 are stacked in this order. In the XY plane, the portion where semiconductor layer 21 and contact layer 22 are disposed is designated as region 29. The length L0 of region 29 is, for example, 200 μm.

[0043] An insulating film 23 is provided on the upper surface of the contact layer 22 and outside the region 29. Within the region 29 and above the contact layer 22, the insulating film 23 has a plurality of openings 27. The openings 27 penetrate the insulating film 23.

[0044] An electrode 26 is disposed on the upper surface of the insulating film 23. The electrode 26 is in contact with the upper surface of the insulating film 23 and in contact with the upper surface of the contact layer 22 at the opening 27, and is electrically connected to the contact layer 22. The inner side of the opening 27 is filled with the electrode 26. The electrode 24 is in contact with the lower surface of the substrate 10 and is electrically connected to the substrate 10 and the covering layer 12.

[0045] 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.

[0046] 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.

[0047] 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 aluminum gallium indium arsenide (AlGaInAs). The active layer 18 provides optical gain.

[0048] The cladding layer 20 is formed, for example, of p-type indium phosphide (p-InP) with a thickness of 3 μm. The semiconductor layer 21 is formed, for example, of p-type indium gallium arsenide phosphide (p-InGaAsP) with a thickness of 100 nm. The contact layer 22 is formed, for example, of p-type indium gallium arsenide (p-InGaAs) with a thickness of 200 nm. The p-type dopant is, for example, zinc (Zn) or carbon (C). The insulating film 23 is formed of an insulator such as silicon nitride (SiN). The above materials are examples; each layer can be formed of other materials, or a combination of the above materials and other materials.

[0049] 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 the parent material of the photonic crystal layer 14, namely InGaAsP, is higher than that of the cladding layer, for example, 3.4.

[0050] Figure 2A This is a top view illustrating a photonic crystal layer 14. The lengths L1 and L2 of one side are, for example, 1000 μm. Region 15 of the photonic crystal layer 14 is located at the center of the photonic crystal layer 14. The planar shape of region 15 is circular. The diameter D1 of region 15 is, for example, 300 μm. A hole is provided in region 15. If the photonic crystal surface emits a laser 100 viewed from the Z-axis direction, then region 15 and... Figure 1 Region 29 overlaps.

[0051] Figure 2B This is a magnified top view of region 15 of the photonic crystal layer 14. Figure 2C This is an enlarged cross-sectional view of the photonic crystal layer 14, illustrating the cross-section along... Figure 2B The cross-section of line AA. The photonic crystal layer 14 has a substrate 30 (first region), voids 32 (second region), and voids 34 (second region). The substrate 30 is an InGaAsP layer, etc., as described above. A plurality of voids 32 and a plurality of voids 34 are provided in the substrate 30.

[0052] like Figure 2BAs shown, a plurality of voids 32 and 34 are arranged in a two-dimensional configuration. The voids 32 are arranged in a square lattice. The voids 34 are arranged in a square lattice. The voids 32 and 34 are periodically arranged in the X-axis and Y-axis directions. The lattice constant is, for example, 400 nm. That is, the distance between adjacent voids 32 and the distance between adjacent voids 34 in the X-axis and Y-axis directions are 400 nm. The planar shape of the void 32 is elliptical. The major and minor axes of the void 32 are inclined from the direction in which the voids 32 are arranged. The planar shape of the void 34 is circular.

[0053] like Figure 2C As shown, holes 32 and 34 extend along the Z-axis. One end of each hole 32 and 34 is located on one face of the photonic crystal layer 14. The other end of each hole 32 and 34 is located midway through the photonic crystal layer 14. Holes 32 and 34 can penetrate the photonic crystal layer 14 and extend to the cladding layer 12. Hole 32 is longer than hole 34. The interiors of holes 32 and 34 are filled with air. The refractive indices of holes 32 and 34 are different from those of the parent material 30. Within the face of the photonic crystal layer 14, the refractive index changes periodically.

[0054] Figure 3A This is a bottom view illustrating an example of a photonic crystal surface-emitting laser 100. (Example:) Figure 3A As shown, an opening 25 is provided in the electrode 24. The planar shape of the opening 25 is circular. The diameter D2 of the opening 25 is, for example, 340 μm. The opening 25 penetrates the electrode 24, and the substrate 10 is exposed from the opening 25. The opening 25 functions as an aperture for emitting light. The surface of the substrate 10 inside the opening 25 can be covered by an insulating film.

[0055] 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 one side close to substrate 10.

[0056] Figure 3B This is a top view illustrating a photonic crystal surface-emitting laser 100, showing the electrode 26. The electrode 26 covers the entire upper surface of the insulating film 23. In region 29, within the plane of the insulating film 23, a plurality of openings 27 are arranged in a two-dimensional configuration. The planar shape of the openings 27 is, for example, rectangular. The length L3 of one side of an opening 27 is, for example, 1.6 μm. The distance (spacing L4) between corresponding sides of adjacent openings 27 is, for example, 5 μm. The area fill factor (FF) of the openings 27 is calculated by the following formula and is approximately 10%.

[0057] FF = (L3) 2 / (L4)2 The contact layer 22 is exposed from multiple openings 27, and the electrode 26 contacts the contact layer 22. That is, the electrode 26 has a mesh structure and periodically contacts the contact layer 22 in the XY plane. In the region between adjacent openings 27, an insulating film 23 is disposed between the electrode 26 and the contact layer 22. The electrode 26 is a p-type electrode, for example, formed by stacking titanium (Ti), platinum (Pt), and gold (Au) from the side near the contact layer 22. The electrode 26 may also be an electrode in which an Au layer is stacked on top of a Ti layer.

[0058] 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 via electrodes 24 and 26. Charge carriers are injected into the active layer 18, thereby generating light. Within the plane of the photonic crystal layer 14, the light is diffracted and scattered, and light with wavelengths corresponding to the periods of apertures 32 and 34 is amplified, resulting in laser oscillation. The laser wavelengths are, for example, in the 1.3 μm band and the 1.5 μm band.

[0059] The laser beam is emitted along the Z-axis. Figure 1 Light propagating downwards exits from the opening 25 of electrode 24. Light propagating upwards is reflected by the lower surface of electrode 26, propagates downwards, and exits from the opening 25.

[0060] The light output depends on the reflectivity of the surface of electrode 26 and the thickness of insulating film 23. By emitting light reflected by electrode 26, the light output can be improved.

[0061] To achieve electrical conductivity between electrode 26 and contact layer 22, heat treatment is performed. However, there is a risk that the lower surface of electrode 26 may become rough due to heat treatment, leading to reduced reflectivity. If electrode 26 is a single-surface electrode, the entire lower surface is in contact with contact layer 22. Due to the large contact area, a rough surface is easily formed, increasing the likelihood of reduced reflectivity. In the first embodiment, as... Figure 1 As shown, electrode 26 is disposed on insulating film 23 and contacts contact layer 22 inside opening 27. Therefore, the contact area between electrode 26 and contact layer 22 is reduced. The portion of electrode 26 in contact with insulating film 23 does not easily become rough even after heat treatment. Therefore, reflectivity is increased.

[0062] The intensity of the emitted light varies depending on the phase of the reflected light from the lower surface of electrode 26 and the phase of the light from the active layer 18 toward the opening 25. When the phases are synchronized, the light is amplified, and the light output is increased. The phase of the reflected light depends on the refractive index and thickness of the insulating film 23. By setting the thickness appropriately, the phase can be adjusted.

[0063] (Reflectivity) The reflectance of four samples, A, B, C, and D, was measured. Sample A consisted of a 180 nm thick SiN layer, a 600 μm thick GaAs substrate, a 160 nm thick SiN layer, a Ti layer, and an Au layer, stacked sequentially. Sample B had the same structure as sample A but lacked a SiN layer between the GaAs and Ti layers. Sample C consisted of a 180 nm thick SiN layer, a 250 μm thick InP substrate, a 40 nm thick InGaAsP layer, a 70 nm thick C-doped InGaAs layer, a 100 nm thick SiN layer, a Ti layer, a Pt layer, and an Au layer, stacked sequentially. Sample D had the same structure as sample C but lacked a SiN layer between the InGaAs and Ti layers.

[0064] Reflectance was obtained by shining light onto the SiN layer of each sample and measuring the reflected light. Sample A had a reflectance of 96%. Sample B had a reflectance of 79%. Sample C had a reflectance of 62%. Sample D had a reflectance of 45%. Samples A and C had a SiN layer between the GaAs and Ti layers. Samples B and D did not have a SiN layer at this location. The reflectance was increased by placing a SiN layer between the semiconductor layer and the metal.

[0065] (Slope efficiency) Figure 4 This is a graph illustrating the slope efficiency. The horizontal axis represents the thickness of the insulating film 23. The vertical axis represents the slope efficiency (SE) of the photonic crystal surface-emitting laser 100. The wavelength of the light is set to 1310 nm. The reflectivity of the electrode 26 at the opening 27 is set to 0.5. The slope efficiency is calculated by setting the refractive index of the insulating film 23 to 1.99 and the refractive index of InP to 3.2.

[0066] Figure 4 The dashed line corresponds to the case where the overall reflectivity of electrode 26 is 0. Higher reflectivity results in higher slope efficiency. Higher slope efficiency leads to higher light output when the current flowing to the photonic crystal surface-emitting laser 100 is increased. The slope efficiency varies periodically with respect to the thickness of the insulating film 23. The period of the slope efficiency waveform is calculated to be approximately 320 nm for the thickness of the insulating film 23. That is, the slope efficiency reaches a minimum at a thickness of 0 nm and approximately 320 nm. It reaches a maximum at a thickness of approximately 160 nm. At the maximum slope efficiency, the overall reflectivity of electrode 26 is 0.5. By setting the thickness of the insulating film 23 appropriately, the phase is adjusted. Light output can be improved by enhancing the emitted and reflected light from the active layer 18.

[0067] (Manufacturing method) Figures 5A to 7BThis is a cross-sectional view illustrating, for example, a method for manufacturing a photonic crystal surface-emitting laser 100. (Example) Figure 5A As shown, for example, a cladding layer 12 and a photonic crystal layer 14 are epitaxially grown on a substrate 10 in this order using metal-organic chemical vapor deposition (MOCVD). In this process, a base material 30 (InGaAsP) is formed for the photonic crystal layer 14, but no voids are formed.

[0068] Figure 5B as well as Figure 5C This is an enlarged view of photonic crystal layer 14. (See image below.) Figure 5B As shown, a mask 50 is disposed on the upper surface of the photonic crystal layer 14. The mask 50 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 the like, and the resist pattern is transferred to the insulating film, thereby forming the mask 50. The mask 50 has an opening 51 and an opening 52. The upper surface of the substrate 30 is exposed through the openings 51 and 52. The plurality of openings 51 and 52 are arranged in a two-dimensional shape.

[0069] like Figure 5C As shown, vias 32 and 34 are formed in the photonic crystal layer 14 using 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. Via 32 is formed at the position on the mask 50 that overlaps with the opening 51. Via 34 is formed at the position that overlaps with the opening 52. The planar shapes of vias 32 and 34 are determined by the planar shapes of the openings 51 and 52. For example, opening 51 is elliptical, and opening 52 is circular. Figure 2B This forms elliptical holes 32 and circular holes 34. After etching, the mask 50 is removed.

[0070] like Figure 6A As shown, an epitaxial layer 16, an active layer 18, an cladding layer 20, a semiconductor layer 21, and a contact layer 22 are grown on top of 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, becoming voids. On the flat cladding layer 16, the active layer 18, the cladding layer 20, the semiconductor layer 21, and the contact layer 22 are epitaxially grown. By adjusting the growth conditions, carbon (C) is doped into the contact layer 22, for example.

[0071] like Figure 6BAs shown, the peripheral portion of the contact layer 22, semiconductor layer 21, and cladding layer 20 is etched. The upper surface of the active layer 18 is exposed from the etched portion. The thickness from the upper surface of the active layer 18 to the upper surface of the contact layer 22 is measured.

[0072] like Figure 6C As shown, the insulating film 23 is formed, for example, by plasma enhanced CVD (PECVD). The thickness of the insulating film 23 is determined based on the thickness from the active layer 18 to the contact layer 22.

[0073] like Figure 7A As shown, a mask 54 is provided on the insulating film 23. A photoresist is used as the mask 54, for example. Multiple openings are formed on the mask 54 by patterning with the photoresist. The portion of the insulating film 23 exposed from the mask 54 is removed by dry etching, forming multiple openings 27. The mask 54 is then removed.

[0074] like Figure 7B As shown, a mask 55 is provided on the outer periphery of the insulating film 23. A photoresist is used as the mask 55, for example. An opening is formed in the portion of the mask 55 that overlaps with the opening 27 by patterning with the photoresist. An electrode 26 is formed by vapor deposition and stripping. For example, a Ti layer, a Pt layer, and an Au layer are sequentially stacked. The mask 55 is then removed. On the lower surface of the substrate 10, as shown... Figure 1 Electrode 24 is arranged as shown, forming opening 25. For example, heat treatment is performed at a temperature above 300°C to achieve contact between the electrode and the semiconductor. The wafer is cut by scribing the outer periphery. The photonic crystal surface-emitting laser 100 is formed through the above processes.

[0075] According to the first embodiment, the insulating film 23 has a plurality of openings 27. For example... Figure 1 As shown, electrode 26 is disposed on the upper surface of insulating film 23 and contacts the upper surface of contact layer 22 through opening 27, thus being electrically connected to contact layer 22. Because insulating film 23 is disposed between contact layer 22 and electrode 26, the contact area between electrode 26 and contact layer 22 is reduced. Even after heat treatment, the lower surface of electrode 26 is less prone to roughening. The reflectivity of the lower surface of electrode 26 is increased. Light is less easily scattered and is reflected by electrode 26 and emitted from opening 25. Light output is increased.

[0076] By setting the thickness of the insulating film 23 to the desired size, the phase of the reflected light is adjusted. When the phase difference between the reflected light and the emitted light from the active layer 18 is 2nπ (n=0, 1, 2...), the light is enhanced and the light output increases.

[0077] For example in Figure 6BIn the process of manufacturing, before the insulating film 23 is formed, the thickness of the semiconductor layer from the active layer 18 to the contact layer 22 is measured. Based on this thickness, the thickness of the insulating film 23 is determined. By controlling the thickness of the insulating film 23 to an optimal value during manufacturing, the phase of light can be adjusted and the light output improved. For example, in... Figure 4 The thickness with the highest slope efficiency is selected. The thickness of the insulating film 23 is controlled, for example, by the film formation time.

[0078] like Figure 3B As shown, multiple openings 27 are periodically arranged in the X-axis and Y-axis directions. The electrode 26 is electrically connected to the contact layer 22 through the multiple openings 27. Current can be uniformly injected into the active layer 18. The arrangement of the openings 27 can also be non-periodic, but this poses a risk of current deviation. The openings 27 are periodically arranged at a certain interval L4, thereby making the current nearly uniform.

[0079] If the fill factor (FF) of the multiple openings 27 in region 29 is small, the contact area between electrode 26 and contact layer 22 decreases, and the contact resistance increases. If the FF is large, the contact area increases, and the area of ​​electrode 26 on insulating film 23 decreases. The lower surface becomes rougher, and the reflectivity decreases. FF can be set, for example, to 5% or more and 50% or less, or to 10% or more, 20% or more, 40% or less, or 45% or less. This can suppress contact resistance and improve reflectivity.

[0080] If the opening 27 is small, manufacturing becomes difficult. If the opening 27 is large, it is difficult to inject current uniformly. The opening 27 is rectangular, and the length L3 of the opening 27 is, for example, set to be more than 1 μm and less than 10 μm. The length L3 can be more than 2 μm, more than 3 μm, less than 8 μm, or less than 9 μm. The opening 27 is easy to manufacture and can inject current uniformly.

[0081] The insulating film 23 is formed of SiN with a refractive index of 1.99. The phase of light depends on the refractive index and the thickness. The thickness is controlled by dividing the product of the thickness of the SiN insulating film 23 and the refractive index by the wavelength of light in a way that is an integer multiple of 2π. This allows for phase adjustment and improved reflectivity.

[0082] C is doped into contact layer 22. This is achieved by setting the C concentration to 1 × 10⁻⁶. 19 cm -3 The above can reduce contact resistance. This is achieved by increasing the C concentration, for example, to 1 × 10⁻⁶. 20 cm -3 In comparison to Zn doping, the contact resistance between the contact layer 22 and the electrode 26 is reduced to about 1 / 10.

[0083] The substrate 10, cladding layer 12, photonic crystal layer 14, and cladding layer 16 have n-type conductivity. The active layer 18 is undoped. The cladding layer 20 and contact layer 22 have p-type conductivity. By stacking these layers, a pin junction (positive-intrinsic-negative) is formed. The electrode 26 is connected to the p-type contact layer 22 at the opening 27. A voltage can be applied to the electrode to inject carriers into the active layer 18. Alternatively, the conductivity can be set to the opposite of the above. An n-type layer is provided on one side of the active layer 18, and a p-type layer is provided on the opposite side.

[0084] There are two types of voids, but there can be one type or more than three types. The planar shape of the voids can 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 cladding layer 20, between the cladding layer 12 and the active layer 18, or between the active layer 18 and the cladding layer 20.

[0085] <Second Implementation> Figure 8 This is a cross-sectional view illustrating a photonic crystal surface-emitting laser 200 according to the second embodiment. Descriptions of configurations identical to those in the first embodiment are omitted. The electrode 26 has multiple metal layers 40 (first metal layers) and metal layers 42 (second metal layers). Metal layers 40 are disposed at openings 27 of the insulating film 23 and contact the upper surface of the contact layer 22. Metal layers 42 are disposed on the upper surfaces of the insulating film 23 and the metal layers 40, and contact these surfaces.

[0086] Metal layer 40 is formed by stacking a Ti layer, a Pt layer, and an Au layer from the side closest to contact layer 22. Metal layer 42 is formed by stacking a Ti layer, a Pt layer, and an Au layer from the side closest to insulating film 23. The thickness of the Ti layer in metal layer 42 is thinner than the thickness of the Ti layer in metal layer 40. Electrode 26 may be formed of a metal other than those described above.

[0087] (Slope efficiency) Figure 9 This diagram illustrates the light output. The horizontal axis represents the current flowing through the photonic crystal surface-emitting laser. The vertical axis represents the light output. The dotted line represents Comparative Example 1. The dashed line represents Comparative Example 2. The solid line represents the second embodiment. In Comparative Examples 1 and 2, the entire upper surface of the contact layer 22 is exposed from the insulating film 23. The electrode 26 is a full-surface electrode, making full contact with the upper surface of the contact layer 22. The electrode 26 in Comparative Example 1 has the same configuration as the metal layer 40 described above. The electrode 26 in Comparative Example 2 has the same configuration as the metal layer 42 described above.

[0088] like Figure 9 As shown, the tilt angle of the second embodiment is larger than that of Comparative Example 1 and Comparative Example 2. Comparative Example 1 has a slope efficiency of 0.19 W / A and a maximum light output of 224 mW. Comparative Example 2 has a slope efficiency of 0.17 W / A and a maximum light output of 193 mW. The second embodiment has a slope efficiency of 0.41 W / A and a maximum light output of 365 mW. According to the second embodiment, the slope efficiency of the photonic crystal surface-emitting laser 200 is more than twice that of Comparative Example 1 and Comparative Example 2. The light output of the photonic crystal surface-emitting laser 200 can be increased to 300 mW or more.

[0089] Verify the change in slope efficiency when the thickness of insulating film 23 is varied. First, calculate the change in reflectivity. Figure 10 This is a graph showing the calculated reflectance. The horizontal axis represents the thickness of the insulating film 23. The vertical axis represents the overall reflectance of the lower surface of the electrode 26. The black circle represents the total reflectance in all directions. The white circle represents the reflectance in the vertical direction (…). Figure 8 The reflectivity in the downward direction (the area below the light source). The difference between the total reflectivity and the vertical reflectivity is equivalent to the light scattering loss. The higher the vertical reflectivity, the higher the light output.

[0090] The slope efficiency is calculated. The following parameters are used in the slope efficiency calculation: absorption coefficient A, wavelength λ, quantum efficiency ηi, reflectivity R, light loss αv, α||, α0 depending on the polarization direction, and phase θ. Phase θ is expressed by the following formula.

[0091] [Mathematical Expression 1]

[0092] T1 is the total thickness of the multiple semiconductor layers from the reflection point of the photonic crystal layer 14 to the lower surface of the insulating film 23. T2 is the thickness of the insulating film 23. n1 is the equivalent refractive index of the semiconductor layer (the layer from the substrate 10 to the contact layer 22). n2 is the refractive index of the insulating film 23. B is the adjustment parameter for the phase deviation of light.

[0093] In three photonic crystal surface-emitting lasers 200 (chips E to G), the thickness of the insulating film 23 is varied, and the slope efficiency is calculated. In the three chips, the refractive index n1 is 3.3, n2 is 1.78, the total film thickness T1 is 2700 nm, the wavelength is 1330 nm, and the loss α0 is 4.5 cm. -1 The area fill rate of the opening 27 in chip E is 10%, and the loss αv is 11.5 cm. -1 The loss α|| is 9.5cm -1The area fill factor in chip F is 13%, and the loss αv is 12cm. -1 The loss α|| is 11.5cm. -1 The area fill factor in chip G is 16.8%, and the loss αv is 11.5 cm. -1 The loss α|| is 18cm -1 As the reflectivity R, use Figure 10 The value in the vertical direction.

[0094] Figures 11A to 11C This is a graph representing the slope efficiency, showing the results for chips E, F, and G respectively. The horizontal axis represents the film thickness of insulating film 23. The vertical axis represents the slope efficiency. The solid line represents the calculated slope efficiency. The slope efficiency varies periodically with changes in film thickness. By using... Figure 10 The variation in reflectivity shown and mathematical formula 1 enable high-precision calculation of slope efficiency.

[0095] (Manufacturing method) Figure 12A as well as Figure 12B This is a cross-sectional view illustrating, by way of example, the manufacturing method of a photonic crystal surface-emitting laser 200. Figure 7A The processes described above are also common in the second embodiment. For example... Figure 12A As shown, a mask 56 is disposed on the insulating film 23. An opening is formed in the mask 56 that overlaps with the opening 27 by patterning with a photoresist. Multiple metal layers 40 are formed in the opening 27 by vapor deposition and stripping. The mask 56 is then removed.

[0096] A mask 57 is provided on the outer periphery for resist patterning. A metal layer 42 is formed on the insulating film 23 and the metal layer 40 by vapor deposition and stripping. Then, the mask 57 is removed. For example, heat treatment is performed at a temperature above 300°C to achieve contact between the electrode and the semiconductor. The above processes form a photonic crystal surface-emitting laser 200.

[0097] According to the second embodiment, since an insulating film 23 is provided between the contact layer 22 and the electrode 26, the contact area between the electrode 26 and the contact layer 22 is reduced. This results in higher reflectivity and increased light output.

[0098] Electrode 26 has a metal layer 40 and a metal layer 42. Metal layer 40 is in contact with contact layer 22. Metal layer 42 is located above insulating film 23 and has a higher reflectivity than metal layer 40. This achieves a balance between electrical conductivity and high reflectivity. The Ti layer of metal layer 42 is thinner than the Ti layer of metal layer 40. The reflectivity of metal layer 42 is thus higher.

[0099] like Figures 11A to 11CAs shown, the phase of the reflected light is adjusted by changing the thickness of the insulating film 23. When the phase difference between the reflected light and the emitted light from the active layer 18 is 2nπ (n=0, 1, 2...), the light is enhanced and the light output increases.

[0100] <Third Implementation Method> Figure 13A This is a top view illustrating the photonic crystal surface-emitting laser 300 according to the third embodiment, showing the electrode 26. Descriptions of configurations identical to those in the first or second embodiment are omitted. The electrode 26 may be the same as in the first embodiment or the second embodiment.

[0101] like Figure 13A As shown, the planar shape of the opening 27 is rectangular. The length L5 of the opening 27 in the X-axis direction is, for example, 1 μm or more and 10 μm or less. The length L6 in the Y-axis direction is longer than L5, for example, 200 μm. The openings 27 of the insulating film 23 are arranged periodically in the X-axis direction. The spacing L7 is, for example, 5 μm. The FF of the opening 27 is 5% or more and 10% or less.

[0102] According to the third embodiment, electrode 26 contacts the upper surface of contact layer 22 through opening 27. The contact area between electrode 26 and contact layer 22 is reduced. Reflectivity increases, and light output increases.

[0103] <Fourth Implementation> Figure 13B This is a top view illustrating the photonic crystal surface-emitting laser 400 according to the fourth embodiment, showing the electrode 26. Descriptions of configurations identical to those in the first or second embodiment are omitted. The electrode 26 may be the same as in the first embodiment or the second embodiment.

[0104] like Figure 13B As shown, a plurality of openings 27 are arranged in concentric circles. One of the openings 27, 27a, is circular. Opening 27b is annular and surrounds opening 27a. The width L8 of the openings 27 is, for example, 1 μm or more and 10 μm or less. The spacing L9 is, for example, 5 μm. The outermost opening 27 has an outer diameter of 200 μm. The FF of the openings 27 is 5% or more and 10% or less.

[0105] According to the fourth embodiment, electrode 26 contacts the upper surface of contact layer 22 through opening 27. The contact area between electrode 26 and contact layer 22 is reduced. Reflectivity increases, and light output increases.

[0106] Multiple openings 27 are arranged periodically within the plane of the insulating film 23. The planar shape of the openings 27 can be polygonal, or it can be a shape that includes circles, curves, etc.

[0107] The embodiments of this disclosure have been described in detail above, but this disclosure is not limited to the specific embodiments described above, and various modifications and alterations can be made within the scope of the spirit of this disclosure as set forth in the claims.

Claims

1. A photonic crystal surface-emitting laser, wherein, The photonic crystal surface-emitting laser has the following features: First semiconductor layer; An active layer is stacked on top of the first semiconductor layer; The second semiconductor layer is configured to be opposite to the first semiconductor layer relative to the active layer; A photonic crystal layer is disposed between the first semiconductor layer and the second semiconductor layer; The first electrode is electrically connected to the first semiconductor layer; An insulating film is disposed on the side of the second semiconductor layer opposite to the active layer; as well as The second electrode is disposed on the side of the insulating film opposite to the second semiconductor layer. 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 insulating film has multiple openings. In the plurality of openings, the second electrode is electrically connected to the second semiconductor layer.

2. The photonic crystal surface-emitting laser according to claim 1, wherein, The plurality of openings are periodically disposed within the surface of the insulating film.

3. The photonic crystal surface-emitting laser according to claim 1 or 2, wherein, The area fill rate of the plurality of openings relative to the region where the second semiconductor layer is disposed is 5% or more and less than 50%.

4. The photonic crystal surface-emitting laser according to claim 1 or 2, wherein, The planar shape of the opening is rectangular. The length of the opening is more than 1 μm and less than 10 μm.

5. The photonic crystal surface-emitting laser according to claim 1 or 2, wherein, The second electrode comprises a first metal layer and a second metal layer. The reflectivity of the second metal layer is higher than that of the first metal layer. The first metal layer is disposed at the plurality of openings of the insulating film, and the second metal layer is disposed on the surface of the insulating film.

6. The photonic crystal surface-emitting laser according to claim 1 or 2, wherein, The photonic crystal surface-emitting laser includes a third semiconductor layer disposed between the active layer and the second semiconductor layer. The first semiconductor layer has an n-type conductivity. The second semiconductor layer and the third semiconductor layer have p-type conductivity.

7. A method for manufacturing a photonic crystal surface-emitting laser, wherein, The method for manufacturing the photonic crystal surface-emitting laser includes: The process of stacking an active layer on top of the first semiconductor layer; The process of forming a photonic crystal layer; The process of forming a second semiconductor layer opposite to the first semiconductor layer, relative to the active layer; The process of forming a first electrode electrically connected to the first semiconductor layer; The process of forming an insulating film on the side of the second semiconductor layer opposite to the active layer; The process of forming multiple openings in the insulating film; as well as The process of forming a second electrode on the side of the insulating film opposite to the second semiconductor layer. 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. In the plurality of openings, the second electrode is electrically connected to the second semiconductor layer.

8. The method for manufacturing a photonic crystal surface-emitting laser according to claim 7, wherein, The method for manufacturing the photonic crystal surface-emitting laser includes a step of stacking a third semiconductor layer on the active layer. The second semiconductor layer is stacked on top of the third semiconductor layer. In the process of forming the insulating film, the insulating film is formed having a thickness based on the thickness from the active layer to the second semiconductor layer.

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