Visible light wave band photonic crystal surface emitting laser and preparation method thereof

Abstract

The invention discloses a visible light wave band photonic crystal surface emitting laser and a preparation method thereof. The visible light wave band photonic crystal surface emitting laser comprises a first semiconductor layer, a columnar structure array and a second semiconductor layer. The first semiconductor layer and the second semiconductor layer are used for conducting current; the columnar structure array comprises a plurality of columnar structures which are periodically arranged; the columnar structure is a multi-layer structure comprising an optical confinement structure layer; the tops of the multiple columnar structures make contact with one another, so that the upper surface of the columnar structure array forms a seamless plane, the second semiconductor layer stacked on the seamless plane is a continuous thin film, current can be expanded in the horizontal direction, and due to the fact that the second semiconductor layer is the continuous thin film, the current can be expanded in the horizontal direction. The electrode deposited on the second semiconductor layer subsequently does not cause short circuit of the device due to the fact that the conductive electrode material is deposited in the gap and the side wall of the columnar structure array, thereby simplifying the preparation process of the device and reducing the cost.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductors, and in particular relates to a visible light band photonic crystal surface emitting laser and a preparation method thereof. Background Art

[0002] Vertical cavity surface emitting laser (VCSEL) diodes use distributed Bragg reflectors (DBRs) to achieve optical feedback and emit coherent beams vertically from the device surface. They have the advantages of low threshold current, round and low divergence output beams, etc. In theory, VCSELs based on GaN (gallium nitride) substrates are expected to achieve laser emission in the visible and ultraviolet spectra, but due to the reflectivity and conductivity limitations of GaN-based DBRs, the development of GaN-based electrically pumped VCSELs still faces a series of challenges. DBRs are composed of two material layers with different refractive indices stacked alternately to provide extremely high reflectivity and good conductivity. For GaN-based VCSEL devices, the materials that can be used include GaN, AlN (aluminum nitride), InN (indium nitride), and their ternary alloys. However, there are large lattice mismatches between GaN and AlN and between GaN and InN, which are about 2.5% and 11%, respectively, and the p-type conductivity is poor, resulting in the disadvantages of high resistivity, large defect density and dislocations, and low reflectivity in GaN-based DBRs for shorter operating wavelengths. Therefore, preparing a DBR-free optical feedback structure has become a new technical route for preparing GaN basal surface emitting lasers.

[0003] Two-dimensional photonic crystals can form optical feedback in the plane. The reciprocal lattice of the photonic crystal structure used in the surface-emitting laser has six equivalent gamma points in the Brillouin zone. These points are coupled to each other in the plane through the Bragg grating vector. The corresponding light wavelength forms a standing wave resonance in the photonic crystal without DBR. In addition to the optical feedback formed by the in-plane coupling, there is also out-of-plane coupling between the six gamma points and the gamma point with zero in-plane wave vector, thus forming a vertical laser surface emission output, which can get rid of the dependence of VCSEL devices on high-quality DBR structures.

[0004] For two-dimensional photonic crystals formed by columnar arrays, an etching preparation process is usually used to form a periodic photonic crystal subwavelength structure. However, the etching process can cause side wall damage and form a large number of surface states on the side wall surface, resulting in a higher surface non-radiative recombination rate and reducing the luminescence efficiency. The active area of ​​the device undergoes stress relaxation after the mesa etching is completed, and the luminescent wavelength of the active area shifts, reducing the controllability of the device's luminescent wavelength.

[0005] In order to improve the luminescence performance of photonic crystal surface emitting lasers and overcome the problems of wavelength shift and sidewall damage, a bottom-up grown micro-nanostructure represented by nanopillars was proposed, which alleviated the problems of large lattice adaptation and high stress, and can incorporate indium gallium nitride with a higher indium content (SID Symposium Digest of Technical Papers, Volume 53, Issue S1, 2022, pp 124-124). Since the indium gallium nitride layer is not etched, the wavelength shift and sidewall damage problems associated with etching are avoided (Japanese Journal of Applied Physics, Volume 63, Issue 3, 2024).

[0006] However, there are gaps between the separated micro- or nano-pillars. In order to prepare a certain area of ​​photonic crystal surface emitting laser, the gaps need to be filled before the electrodes can be deposited. Otherwise, the deposition of conductive electrode materials will easily cause a short circuit between the top and bottom of the nano-pillars. Therefore, the preparation process of photonic crystal surface emitting lasers is relatively complicated, which increases the cost of this technical path and requires further simplification of the process. Summary of the invention

[0007] In order to solve the above problems existing in the prior art, the present invention provides a visible light band photonic crystal surface emitting laser and a preparation method thereof.

[0008] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0009] In a first aspect, the present invention provides a visible light band photonic crystal surface emitting laser, comprising:

[0010] A first semiconductor layer; the first semiconductor layer is used for conducting current;

[0011] A columnar structure array; the columnar structure array is superimposed on the first semiconductor layer; the columnar structure array includes a plurality of columnar structures arranged in a periodic manner; the columnar structure is a multilayer structure; the tops of the plurality of columnar structures are in contact with each other, so that the upper surface of the columnar structure array forms a seamless plane;

[0012] A second semiconductor layer; the second semiconductor layer is superimposed on the seamless plane; the second semiconductor layer is used for conducting current.

[0013] Optionally, the columnar structure includes, from bottom to top, a first doped Group III nitride semiconductor, a first cladding layer, a waveguide layer, a second cladding layer and a second doped Group III nitride semiconductor.

[0014] Optionally, the materials of the first cladding layer and the second cladding layer are both AlGaN with an Al content greater than 5%.

[0015] Optionally, the waveguide layer includes a first sub-waveguide layer, a quantum confinement layer superimposed on the first sub-waveguide layer, and a second sub-waveguide layer superimposed on the quantum confinement layer; the quantum confinement layer is a single quantum confinement layer or a plurality of stacked quantum confinement layers; in the plurality of stacked quantum confinement layers, a barrier layer is arranged between every two quantum confinement layers; the materials of the first sub-waveguide layer and the second sub-waveguide layer are both GaN or InGaN with a Ga content greater than 70%; the material of the quantum confinement layer is InGaN with an In content greater than 5%; the material of the barrier layer is GaN or InGaN with an In content less than the In content in the quantum confinement layer.

[0016] Optionally, the doping types of the first semiconductor layer and the first doped Group III nitride semiconductor are both the first doping type; and the doping types of the second doped Group III nitride semiconductor and the second semiconductor layer are both the second doping type.

[0017] Optionally, the columnar structure array further includes a third doped group III nitride semiconductor; the third doped group III nitride semiconductor is superimposed on the second doped group III nitride semiconductor;

[0018] The doping types of the first semiconductor layer, the second semiconductor layer, the first doped III-nitride semiconductor and the third doped III-nitride semiconductor are all the first doping type; the doping type of the second doped III-nitride semiconductor is the second doping type; the second doped III-nitride semiconductor and the third doped III-nitride semiconductor in contact therewith form a tunnel junction.

[0019] Optionally, the columnar structure array further includes a third doped group III nitride semiconductor; the third doped group III nitride semiconductor is superimposed below the first doped group III nitride semiconductor;

[0020] The doping types of the first semiconductor layer, the second semiconductor layer, the second doped III-nitride semiconductor and the third doped III-nitride semiconductor are all the first doping type; the doping type of the first doped III-nitride semiconductor is the second doping type; the third doped III-nitride semiconductor and the first doped III-nitride semiconductor in contact therewith form a tunnel junction.

[0021] Optionally, the visible light band photonic crystal surface emitting laser further includes a first electrode and a second electrode;

[0022] The first electrode contacts an upper surface of the first semiconductor layer; and the second electrode contacts an upper surface of the second semiconductor layer.

[0023] In a second aspect, the present invention provides a method for preparing a photonic crystal surface emitting laser in the visible light band, the preparation method comprising:

[0024] Selecting a substrate, and sequentially epitaxially growing an unintentionally doped layer and a doped semiconductor layer on the upper surface of the substrate;

[0025] A columnar array is etched downward on the upper surface of the doped semiconductor layer, and a multi-layer structure is epitaxially grown upward from the etched portion of the upper layer in the doped semiconductor layer to form a columnar structure array; a first semiconductor layer is formed from the unetched portion of the lower layer in the doped semiconductor layer; wherein, when growing the uppermost layer of the columnar structure array, the tops of the columnar structures in the columnar structure array are contacted with each other by increasing the lateral growth rate, so that the upper surface of the columnar structure array forms a seamless plane;

[0026] A second semiconductor layer is epitaxially grown upward on the gap-free plane.

[0027] Optionally, methods of increasing the lateral growth rate include:

[0028] When the uppermost part of the columnar structure is grown by a metal organic chemical vapor deposition process, the lateral growth rate is increased by increasing the growth temperature, ammonia flow rate and Ga precursor flow rate; or when the uppermost part of the columnar structure is grown by a molecular beam epitaxy process, the lateral growth rate is increased by increasing the Ga beam flow, nitrogen flow rate, nitrogen plasma source power, etc.

[0029] The tops of multiple columnar structures in a columnar structure array in a visible light band photonic crystal surface emitting laser provided by the present invention are in contact with each other, so that the upper surface of the columnar structure array forms a seamless plane. Therefore, the second semiconductor layer superimposed on the seamless plane is a continuous thin film, which can expand the current in the horizontal direction and allow the current to flow between the first semiconductor layer and the second semiconductor layer through the columnar structure array.

[0030] And because the second semiconductor layer is a continuous thin film, the electrodes subsequently deposited on the second semiconductor layer will not cause short circuits in the device due to the conductive electrode material being deposited in the gaps and on the side walls of the columnar structure array, thereby simplifying the preparation process of the visible light band photonic crystal surface emitting laser and reducing costs.

[0031] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1It is a schematic structural diagram of a visible light band photonic crystal surface emitting laser provided by an embodiment of the present invention;

[0033] Figure 2 It is a schematic flow chart of a method for preparing a visible light band photonic crystal surface emitting laser provided by an embodiment of the present invention;

[0034] Figure 3(a) to Figure 3(e) A schematic diagram showing a process for preparing a visible light band photonic crystal surface emitting laser provided by an embodiment of the present invention is shown;

[0035] Figure 4 is a schematic diagram of preparing a first electrode provided by an embodiment of the present invention;

[0036] FIG. 5( a ) and FIG. 5( b ) are schematic diagrams of preparing the second electrode provided in an embodiment of the present invention.

[0037] Figure numerals: 1, substrate; 2, unintentional doping layer; 3, first semiconductor layer; 4, first doped III-nitride semiconductor lower layer; 5, first doped III-nitride semiconductor upper layer; 6, optical confinement structure layer; 61, second cladding layer; 62, waveguide layer; 63, first cladding layer; 7, second doped III-nitride semiconductor lower layer; 8, second doped III-nitride semiconductor upper layer; 9, second semiconductor layer; 10, doped semiconductor layer; 11, first electrode; 12, second electrode. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0039] In order to solve the technical problems of complex preparation process and high cost of the existing photonic crystal surface emitting laser, the embodiment of the present invention provides a photonic crystal surface emitting laser in the visible light band, see Figure 1 , Figure 1 1 is a schematic structural diagram of a visible light band photonic crystal surface emitting laser provided by an embodiment of the present invention. The visible light band photonic crystal surface emitting laser comprises a first semiconductor layer 3, a columnar structure array and a second semiconductor layer 9.

[0040] In the embodiment of the present invention, both the first semiconductor layer 3 and the second semiconductor layer 9 are used to conduct current. Specifically, the material of the first semiconductor layer 3 is a group III nitride semiconductor with a Ga (gallium) content of not less than 50% or an Al (aluminum) content of not less than 50%; the material of the second semiconductor layer 9 is a group III nitride semiconductor with a Ga content of not less than 50% or an Al content of not less than 50%.

[0041] In the embodiment of the present invention, the columnar structure array is superimposed on the first semiconductor layer 3. The columnar structure array includes a plurality of columnar structures arranged in a periodic manner. The columnar structure is a multilayer structure, the diameter of the upper end of the columnar structure is larger than the diameter of the lower end, and the tops of the plurality of columnar structures are in contact with each other, so that the upper surface of the columnar structure array forms a seamless plane.

[0042] Specifically, the columnar structure may be a hexagonal columnar structure, the maximum diameter of which is less than 10 μm.

[0043] In the embodiment of the present invention, the columnar structure includes, from bottom to top, a first doped Group III nitride semiconductor, a first cladding layer 63 , a waveguide layer 62 , a second cladding layer 61 , and a second doped Group III nitride semiconductor.

[0044] The first cladding layer 63 , the waveguide layer 62 and the second cladding layer 61 together constitute the optical confinement structure layer 6 .

[0045] In the embodiment of the present invention, the materials of the first cladding layer 63 and the second cladding layer 61 are both AlGaN (aluminum gallium nitride) with an Al content greater than 5%. In AlGaN with an Al content greater than 5%, the Al content is larger, and the refractive index is smaller, so the light can be mainly confined in the waveguide layer 62 with a larger refractive index.

[0046] In the embodiment of the present invention, the first semiconductor layer 3 and the first doped III-nitride semiconductor are both doped with the first doping type; the second doped III-nitride semiconductor and the second semiconductor layer 9 are both doped with the second doping type.

[0047] Specifically, when the first doping type is n-type doping, the second doping type is p-type doping; when the first doping type is p-type doping, the second doping type is n-type doping.

[0048] For example, when the doping type of the first semiconductor layer 3 and the first doped III-nitride semiconductor is n-type doping, the doping type of the second doped III-nitride semiconductor and the second semiconductor layer 9 is p-type doping. Conversely, when the doping type of the first semiconductor layer 3 and the first doped III-nitride semiconductor is p-type doping, the doping type of the second doped III-nitride semiconductor and the second semiconductor layer 9 is n-type doping.

[0049] Electrons and holes are injected from the first doped Group III nitride semiconductor and the second doped Group III nitride semiconductor into the waveguide layer 62 to generate light emission.

[0050] In an embodiment of the present invention, the tops of multiple columnar structures in the columnar structure array are in contact with each other, so that the upper surface of the columnar structure array forms a seamless plane. Therefore, the second semiconductor layer 9 superimposed on the seamless plane is a continuous thin film, which can expand the current in the horizontal direction and allow the current to flow between the first semiconductor layer 3 and the second semiconductor layer 9 through the columnar structure array.

[0051] And because the second semiconductor layer 9 is a continuous thin film, the electrodes subsequently deposited on the second semiconductor layer 9 will not cause short circuits in the device due to the conductive electrode material being deposited in the gaps and on the side walls of the columnar structure array, thereby simplifying the preparation process of the visible light band photonic crystal surface emitting laser and reducing costs.

[0052] In one implementation, the visible light band photonic crystal surface emitting laser further includes a first electrode 11 and a second electrode 12 ; the first electrode 11 contacts the upper surface of the first semiconductor layer 3 ; and the second electrode 12 contacts the upper surface of the second semiconductor layer 9 .

[0053] In the embodiment of the present invention, when the first electrode 11 is an n-type electrode, the material of the first electrode 11 may be Ti (titanium), Cr (chromium), Pt (platinum), Al (aluminum), Au (gold) or a composite layer of these materials.

[0054] When the material of the first electrode 11 is a composite layer of Ti and Au, its thickness can be Ti 20nm and Au 100nm; when the material of the first electrode 11 is a composite layer of Ti, Au and Al, its thickness can be Ti 20nm, Au 100nm and Al 300nm; when the material of the first electrode 11 is Cr, its thickness can be 30nm; when the material of the first electrode 11 is Pt, its thickness can be 30nm; when the material of the first electrode 11 is Au, its thickness can be 50nm.

[0055] When the first electrode 11 is a p-type electrode, the material of the first electrode 11 may be ITO (indium tin oxide), Ni (nickel), Au or a composite layer of these materials. ITO has the characteristics of high transparency, low resistance, good mechanical strength and appropriate toughness.

[0056] Similarly, when the second electrode 12 is an n-type electrode, the material of the second electrode 12 can be Ti, Cr, Pt, Al, Au or a composite layer of these materials. When the second electrode 12 is a p-type electrode, the material of the second electrode 12 can be Ni, Au, ITO or a composite layer of these materials.

[0057] In one implementation, a tunnel junction may also be included in the columnar structure. By adding a heavily doped pn junction as a tunnel junction in the columnar structure, the injection of carriers can be facilitated.

[0058] In one implementation, the columnar structure array including the tunneling junction further includes a third doped III-group nitride semiconductor; wherein the third doped III-group nitride semiconductor is superimposed on the second doped III-group nitride semiconductor. The doping types of the first semiconductor layer 3, the second semiconductor layer 9, the first doped III-group nitride semiconductor and the third doped III-group nitride semiconductor are all the first doping type. The doping type of the second doped III-group nitride semiconductor is all the second doping type. wherein the second doped III-group nitride semiconductor and the third doped III-group nitride semiconductor in contact therewith form a tunneling junction.

[0059] For example, the doping types of the first semiconductor layer 3, the second semiconductor layer 9, the first doped III-group nitride semiconductor, and the third doped III-group nitride semiconductor are all n-type doping, and the doping type of the second doped III-group nitride semiconductor is p-type doping. Conversely, the doping types of the first semiconductor layer 3, the second semiconductor layer 9, the first doped III-group nitride semiconductor, and the third doped III-group nitride semiconductor are all p-type doping, and the doping type of the second doped III-group nitride semiconductor is n-type doping.

[0060] In the embodiment of the present invention, the second doped Group III nitride semiconductor and the third doped Group III nitride semiconductor in contact therewith form a heavily doped pn junction as a tunneling junction to facilitate the injection of carriers.

[0061] In one implementation, the columnar structure array including the tunneling junction further includes a third doped III-group nitride semiconductor; the third doped III-group nitride semiconductor is superimposed below the first doped III-group nitride semiconductor; wherein the doping types of the first semiconductor layer 3, the second semiconductor layer 9, the second doped III-group nitride semiconductor and the third doped III-group nitride semiconductor are all the first doping type; the doping type of the first doped III-group nitride semiconductor is the second doping type. Therefore, the third doped III-group nitride semiconductor and the first doped III-group nitride semiconductor in contact therewith form a tunneling junction.

[0062] For example, the doping types of the first semiconductor layer 3, the second semiconductor layer 9, the second doped III-nitride semiconductor, and the third doped III-nitride semiconductor are all n-type doping, and the doping type of the first doped III-nitride semiconductor is p-type doping. Conversely, the doping types of the first semiconductor layer 3, the second semiconductor layer 9, the second doped III-nitride semiconductor, and the third doped III-nitride semiconductor are all p-type doping, and the doping type of the first doped III-nitride semiconductor is n-type doping.

[0063] In the embodiment of the present invention, the third doped Group III nitride semiconductor and the first doped Group III nitride semiconductor in contact therewith form a heavily doped pn junction as a tunneling junction to facilitate the injection of carriers.

[0064] In addition, for a visible light band photonic crystal surface emitting laser including a tunneling junction, the first cladding layer 63 and the second cladding layer 61 can be swapped. The doping types of the first cladding layer 63 and the second cladding layer 61 are opposite, when the doping type of the first cladding layer 63 is p-type doping, the doping type of the second cladding layer 61 is n-type doping; when the doping type of the first cladding layer 63 is n-type doping, the doping type of the second cladding layer 61 is p-type doping.

[0065] In one implementation, the waveguide layer 62 includes a first sub-waveguide layer, a quantum confinement layer, and a second sub-waveguide layer, wherein the quantum confinement layer is superimposed on the first sub-waveguide layer, and the second sub-waveguide layer is superimposed on the quantum confinement layer.

[0066] In the embodiment of the present invention, the quantum confinement layer may be a single quantum confinement layer or a plurality of quantum confinement layers stacked together.

[0067] The multiple stacked quantum confinement layers refer to multiple quantum confinement layers stacked from bottom to top in a direction perpendicular to the first sub-waveguide layer, and in the multiple stacked quantum confinement layers, a barrier layer is arranged between every two quantum confinement layers.

[0068] For example, when the number of quantum confinement layers is 3, namely quantum confinement layer a, quantum confinement layer b and quantum confinement layer c, quantum confinement layer b is superimposed on quantum confinement layer a, and barrier layer a is arranged between quantum confinement layer a, and quantum confinement layer c is superimposed on quantum confinement layer b, and barrier layer b is arranged between quantum confinement layer b.

[0069] The specific number of quantum confinement layers can be set by technicians according to needs and is not limited here. The thickness of a single quantum confinement layer does not exceed 20 nm, and the thickness of the barrier layer is preferably 6 nm.

[0070] In the embodiment of the present invention, the materials of the first sub-waveguide layer and the second sub-waveguide layer are GaN or InGaN (indium gallium nitrogen) with a Ga (gallium) content greater than 70%, the material of the quantum confinement layer is InGaN with an In content greater than 5%, and the material of the barrier layer is GaN or InGaN with an In content less than the In content in the quantum confinement layer. In plays a role in regulating the band structure and photoelectric properties of InGaN. By changing the In content, the band gap of InGaN can be adjusted, thereby affecting its emission wavelength. When the In content is greater than 5%, the bandgap width of InGaN will decrease, which means that it can emit light in the range of purple, blue, green and even red light.

[0071] In the embodiment of the present invention, when the material of the barrier layer is InGaN, the band gap of the barrier layer can be adjusted to be larger by setting the In content in the material of the barrier layer to be smaller than the In content in the quantum confinement layer.

[0072] In one implementation, the waveguide layer 62 further includes an electron blocking layer, which is superimposed on the quantum confinement layer, wherein the electron blocking layer can be used to reduce electron overflow.

[0073] Specifically, the material of the electron blocking layer may be AlGaN, wherein the content of Al is greater than 20%, and the thickness of the electron blocking layer may be 30 nm.

[0074] The photonic crystal surface emitting laser in the visible light band provided by the embodiment of the present invention has the characteristics of low threshold current density and performance not limited by high-quality DBR and lattice matching. It can be used as a core device structure in the fields of optical fiber communication, intelligent lighting, biosensors, etc.

[0075] Based on the same inventive concept, the present invention also provides a method for preparing a visible light band photonic crystal surface emitting laser, see Figure 2 , Figure 2 1 is a flow chart of a method for preparing a visible light band photonic crystal surface emitting laser provided by an embodiment of the present invention, taking the doping type of the first semiconductor layer 3 as n-type doping and the doping type of the second semiconductor layer 9 as p-type doping as an example, combined with Figure 3(a) to Figure 3(e) The preparation method of the photonic crystal surface emitting laser in the visible light band is described. Figure 3(a) to Figure 3(e) The following is a schematic diagram showing a process for preparing a visible light band photonic crystal surface emitting laser provided by an embodiment of the present invention. The specific steps of the method for preparing a visible light band photonic crystal surface emitting laser are as follows:

[0076] Step S201 , selecting a substrate 1 , and epitaxially growing an unintentionally doped layer 2 and a doped semiconductor layer 10 in sequence on the upper surface of the substrate 1 .

[0077] In the embodiment of the present invention, a substrate 1 with a thickness of 650 μm is first prepared, and the substrate 1 is placed in a reaction chamber of a metal organic vapor deposition system. The substrate 1 is heated to a temperature of 1100° C., and the substrate 1 is subjected to high temperature treatment for 20 minutes in a hydrogen atmosphere. The temperature is then reduced to 515° C., ammonia is introduced into the reaction chamber for 3 minutes, and TMGa (trimethylgallium) is introduced to epitaxially grow a 20 nm GaN nucleation layer. The temperature is then raised to 1050° C., and TMGa and ammonia are introduced to epitaxially grow an unintentionally doped layer 2 and a doped semiconductor layer 10 with a thickness of 1 μm. When growing the doped semiconductor layer 10, SiH4 (monosilane) is introduced at the same time, and the doping concentration is 5×10 18 cm -3, the preparation of the planar n-type doped GaN template is completed, as shown in Figure 3(a).

[0078] Among them, the material of the substrate 1 can be sapphire, silicon, silicon carbide, gallium oxide, zinc oxide, boron nitride, lithium aluminate, lithium niobate, germanium, aluminum nitride or lithium gallate; the unintentionally doped layer 2 can be an unintentionally doped GaN layer, and the doped semiconductor layer 10 can be an n-type doped GaN layer with a thickness of 2μm.

[0079] Step S202, etching the columnar array downward on the upper surface of the doped semiconductor layer 10, and epitaxially growing a multi-layer structure upward from the etched portion of the upper layer in the doped semiconductor layer 10 to form a columnar structure array; the unetched portion of the lower layer in the doped semiconductor layer 10 forms a first semiconductor layer 3; wherein, when growing the uppermost layer of the columnar structure array, the lateral growth rate is increased so that the tops of the columnar structures in the columnar structure array are in contact with each other, so that the upper surface of the columnar structure array forms a seamless plane.

[0080] First, a photoresist with a thickness of 500 nm is evenly spin-coated on the surface of the planar n-type doped GaN template in step S201, and an electron beam lithography machine is used to expose a pattern containing a nanoscale circular array, and then the pattern is developed to obtain a photoresist column array, which is used as a mask layer for etching the n-type doped GaN layer. The period of the array is 250 nm, the diameter of the column is 130 nm, and the distance between the columns is 120 nm.

[0081] A planar n-type doped GaN template having a patterned photoresist column array on its surface is placed in the chamber of an inductively coupled plasma etcher, and the n-type GaN template is etched 600 nm by an inductively coupled plasma etching process in an atmosphere of chlorine and argon. The GaN not covered by the photoresist column array is etched, and a GaN column array is formed in the area covered by the photoresist column array. The template is then placed in a degumming solution and heated in a water bath at 80°C until the remaining photoresist columns are removed to obtain a first doped III-group nitride semiconductor lower layer 4, below which is a continuous unetched n-type doped GaN layer, i.e., a first semiconductor layer 3, as shown in FIG3(b).

[0082] The patterning process may be photolithography or nanoimprinting, and the etching mask layer material may be photoresist, nanoimprinting glue, dielectric or metal.

[0083] The template with the n-type doped GaN column array on the surface is placed in the reaction chamber of the metal organic vapor deposition system to epitaxially grow a part of the photonic crystal surface emitting laser structure, as shown in FIG3(c). The growth steps are as follows:

[0084] 1) The temperature of the reaction chamber is raised to 1020°C, TMGa, SiH4, ammonia and hydrogen are introduced, and a 200 nm thick n-type doped GaN layer, i.e., the first doped III-group nitride semiconductor upper layer 5, is grown on the n-type doped GaN column array template. The concentration of n-type doping is 5×10 18 cm -3 , and the shape of the first doped group III nitride semiconductor changes to a hexagonal column. The first doped group III nitride semiconductor includes a first doped group III nitride semiconductor lower layer 4 and a first doped group III nitride semiconductor upper layer 5.

[0085] 2) Preparation of optical confinement structure layer 6: Growth of first cladding layer 63, waveguide layer 62 and second cladding layer 61. First, the temperature is lowered to 900°C and the gas is switched to TEGa (triethylgallium), SiH4, TMAl (trimethylaluminum), ammonia and hydrogen to grow a 500nm thick first cladding layer 63, wherein the material of the first cladding layer 63 can be n-type doped AlGaN, and the Al content is greater than 10%. Then the temperature is adjusted to 800°C and the gas is switched to TEGa, ammonia and nitrogen. A first waveguide layer with a thickness of 120nm is grown, wherein the material of the first waveguide layer can be GaN. Then the gas is switched to TEGa, TMIn (trimethylindium), ammonia and nitrogen to grow two periods of InGaN / GaN quantum confinement layer and barrier layer. The material of the quantum confinement layer can be InGaN, and its growth temperature is 670°C, the thickness is 2nm, and the In content is 12%. The material of the barrier layer can be GaN, and its growth temperature is 800°C, and the thickness is 6nm. Then, the flow rate and reaction time of TMAl are changed, and a 30nm thick electron blocking layer is continued to grow. The material of the electron blocking layer can be AlGaN, wherein the Al content is greater than 20%. Then, the gas is switched to TEGa, ammonia and nitrogen, and a second sub-waveguide layer with a thickness of 120nm is grown. The material of the second sub-waveguide layer can be GaN. Then, the gas is switched to TEGa, TMAl, bismuth magnesium, ammonia and hydrogen, and a 500nm thick second cladding layer 61 is grown. The material of the second cladding layer 61 can be p-type doped AlGaN, wherein the Al content is greater than 10%, and the growth temperature of AlGaN is 900℃.

[0086] 3) growing a second doped group III nitride semiconductor lower layer 7, switching the gas to TMGa, bismuth magnesium, ammonia and hydrogen, growing a 50 nm second doped group III nitride semiconductor lower layer 7, the material of the second doped group III nitride semiconductor lower layer 7 is p-type doped GaN, and the p-type doping concentration is 1×10 19 cm -3 , completing the epitaxial growth of part of the structure of the photonic crystal surface emitting laser device.

[0087] When growing the top layer of a columnar structure array, the lateral growth rate is increased by increasing the lateral growth rate so that the tops of each columnar structure in the columnar structure array contact each other. The method of increasing the lateral growth rate includes increasing the growth temperature, ammonia flow rate and Ga precursor flow rate to increase the lateral growth rate when growing the top part of the columnar structure using a metal organic chemical vapor deposition process; or increasing the Ga beam flow, nitrogen flow rate, nitrogen plasma source power to increase the lateral growth rate when growing the top part of the columnar structure using a molecular beam epitaxy process.

[0088] Specifically, after the second doped III-nitride semiconductor lower layer 7 is grown, the substrate 1 is heated to 80°C, the ammonia flow rate is increased by 30 times, and the TMGa flow rate is increased by 30%, so that the lateral growth rate is increased, and the p-type doped GaN merging promotion layer, i.e., the second doped III-nitride semiconductor upper layer 8, is continued to grow. As shown in FIG3(d), the tops of the columnar structures in the columnar structure array are contacted with each other by increasing the lateral growth rate, so that the upper surface of the columnar structure array forms a seamless plane, and the preparation of the columnar structure array is completed. Among them, the second doped III-nitride semiconductor includes the second doped III-nitride semiconductor lower layer 7 and the second doped III-nitride semiconductor upper layer 8.

[0089] Step S203, epitaxially growing a second semiconductor layer 9 on a seamless plane.

[0090] In the embodiment of the present invention, a continuous p-type doped GaN layer, namely the second semiconductor layer 9, is epitaxially grown upward on the gap-free plane, as shown in FIG. 3( e ), with a growth thickness of 180 nm. Thus, the growth of the photonic crystal surface emitting laser device is completed.

[0091] In an embodiment of the present invention, the tops of multiple columnar structures in the columnar structure array are in contact with each other, so that the upper surface of the columnar structure array forms a seamless plane. Therefore, the second semiconductor layer 9 superimposed on the seamless plane is a continuous thin film, which can expand the current in the horizontal direction and allow the current to flow between the first semiconductor layer 3 and the second semiconductor layer 9 through the columnar structure array.

[0092] Furthermore, since the second semiconductor layer 9 is a continuous thin film, the electrodes subsequently deposited on the second semiconductor layer 9 will not cause short circuits in the device due to the conductive electrode material being deposited in the gaps and on the side walls of the columnar structure array, thereby simplifying the preparation process and reducing costs.

[0093] Compared with the existing VCSEL (Vertical-Cavity Surface-Emitting Laser), the photonic crystal surface-emitting laser provided by the embodiment of the present invention can realize laser surface emission without using thick, resistive DBR, simplifying the process flow and reducing costs. At the same time, in the preparation process, the photonic crystal surface-emitting laser device structure grown on the stress-relaxed patterned GaN template can effectively relax the stress of the heterostructure.

[0094] In one implementation, the visible light band photonic crystal surface emitting laser further includes a first electrode 11 and a second electrode 12. The first electrode 11 and the second electrode 12 are prepared as follows:

[0095] A photoresist with a thickness of 700 nm was uniformly spin-coated on the substrate surface after the photonic crystal surface emitting laser device was grown. A stepper photolithography machine was used to expose the area where the n-type GaN metal electrode was to be deposited. Then, the surface of the first semiconductor layer 3 was exposed by development. The substrate was placed in the chamber of the electron beam evaporation deposition system. The electron beam evaporation deposition process was used at 1.4×10 -6 Pa or higher vacuum, evaporate n-type GaN metal electrode, i.e., first electrode 11. After the evaporation is completed, put it into the degumming solution and heat it in a water bath at 80°C until the photoresist column is dissolved and removed, and the metal film deposited on the photoresist layer is naturally peeled off, and the metal electrode deposited on the surface of the first semiconductor layer 3 is retained. Figure 4 , Figure 4 Schematic diagram of the preparation of the first electrode 11 provided in an embodiment of the present invention. The substrate is rinsed with water and blown dry with nitrogen. Then, it is placed in a thermal annealing furnace, and the n-type GaN metal electrode is annealed for 18 minutes at a temperature of 550° C. in a nitrogen atmosphere, and the preparation of the first electrode 11 is completed.

[0096] In the embodiment of the present invention, the first electrode 11 is an n-type electrode, and the material of the first electrode 11 can be Ti (titanium), Cr (chromium), Pt (platinum), Al (aluminum), Au (gold) or a composite layer of these materials.

[0097] When the material of the first electrode 11 is a composite layer of Ti and Au, its thickness can be Ti 20nm and Au 100nm; when the material of the first electrode 11 is a composite layer of Ti, Au and Al, its thickness can be Ti 20nm, Au 100nm and Al 300nm; when the material of the first electrode 11 is Cr, its thickness can be 30nm; when the material of the first electrode 11 is Pt, its thickness can be 30nm; when the material of the first electrode 11 is Au, its thickness can be 50nm.

[0098] A photoresist with a thickness of 1600 nm is uniformly spin-coated on the surface of the substrate on which the photonic crystal surface-emitting laser device is grown, and a stepper lithography machine is used to expose the area where the second electrode 12 is to be deposited, and then the surface of the second semiconductor layer 9 is exposed, as shown in FIG5(a). FIG5(a) and FIG5(b) are schematic diagrams of the preparation of the second electrode 12 provided in an embodiment of the present invention. The second semiconductor layer 9 on the surface is a continuous film rather than a separate column array, and an ITO film can be directly deposited as an electrode. The chamber of the substrate magnetron sputtering deposition system is used to deposit an 80 nm thick ITO layer as the second electrode 12 in an argon atmosphere using a magnetron sputtering deposition process. The RF source power used is 150 W, the vacuum degree during sputtering is 0.3 Pa, and the argon flow rate is 14 sccm. After the deposition is completed, the degumming solution is placed in a water bath heated at 80°C until the photoresist is dissolved and removed, and the ITO layer deposited on the photoresist layer is naturally peeled off, and the metal electrode deposited on the surface of the second semiconductor layer 9 is retained, as shown in FIG5(b). The substrate is rinsed with water and blown dry with nitrogen. Then, the ITO electrode is placed in a thermal annealing furnace and annealed for 10 minutes at a temperature of 350° C. in an oxygen atmosphere. Thus, the second electrode 12 on the surface of the second semiconductor layer 9 is prepared.

[0099] In the embodiment of the present invention, the second electrode 12 is a p-type electrode, and the material of the second electrode 12 can be Ni, Au, ITO or a composite layer of these materials. Specifically, it can be a p-type GaN ITO electrode.

[0100] In the embodiment of the present invention, for the existing columnar structure array, it is necessary to first fill the nanowire gaps before depositing the electrode, otherwise it is easy to cause short circuit and leakage. However, since the second semiconductor layer 9 on the upper surface of the device provided by the embodiment of the present invention is a continuous film, the second electrode 12 will not be deposited between the columnar structures and on the side walls of the columnar structures, thereby simplifying the electrode preparation process and reducing costs.

[0101] It should be noted that the terms "first", "second", etc. are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of devices and methods consistent with some aspects of the present invention.

[0102] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0103] Although the present invention is described herein in conjunction with various embodiments, in the process of implementing the claimed invention, those skilled in the art can understand and implement other changes to the disclosed embodiments by viewing the drawings and the disclosed content. In the description of the present invention, the term "comprising" does not exclude other components or steps, "one" or "an" does not exclude multiple situations, and "multiple" means two or more, unless otherwise clearly and specifically limited. In addition, certain measures are recorded in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0104] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0105] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0106] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0107] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A visible light band photonic crystal surface emitting laser, characterized in that: include: A first semiconductor layer; the first semiconductor layer is used for conducting current; Columnar structure array; The columnar structure array is superimposed on the first semiconductor layer; The columnar structure array includes a plurality of columnar structures arranged in a periodic manner; The columnar structure is a multi-layer structure; The tops of the plurality of columnar structures are in contact with each other, so that the upper surface of the columnar structure array forms a seamless plane; a second semiconductor layer; The second semiconductor layer is superimposed on the seamless plane; the second semiconductor layer is used for conducting current.

2. The visible light band photonic crystal surface emitting laser according to claim 1, characterized in that: The columnar structure includes, from bottom to top, a first doped Group III nitride semiconductor, a first cladding layer, a waveguide layer, a second cladding layer, and a second doped Group III nitride semiconductor.

3. The visible light band photonic crystal surface emitting laser according to claim 2, characterized in that: The materials of the first cladding layer and the second cladding layer are both AlGaN with an Al content greater than 5%.

4. The visible light band photonic crystal surface emitting laser according to claim 2, characterized in that: The waveguide layer includes a first sub-waveguide layer, a quantum confinement layer superimposed on the first sub-waveguide layer, and a second sub-waveguide layer superimposed on the quantum confinement layer; the quantum confinement layer is a single quantum confinement layer or a plurality of stacked quantum confinement layers; in the plurality of stacked quantum confinement layers, a barrier layer is arranged between every two quantum confinement layers; the materials of the first sub-waveguide layer and the second sub-waveguide layer are GaN or InGaN with a Ga content greater than 70%; the material of the quantum confinement layer is InGaN with an In content greater than 5%; the material of the barrier layer is GaN or InGaN with an In content less than the In content in the quantum confinement layer.

5. The visible light band photonic crystal surface emitting laser according to claim 2, characterized in that: The doping types of the first semiconductor layer and the first doped Group III nitride semiconductor are both the first doping type; the doping types of the second doped Group III nitride semiconductor and the second semiconductor layer are both the second doping type.

6. The visible light band photonic crystal surface emitting laser according to claim 2, characterized in that: The columnar structure array further includes a third doped group III nitride semiconductor; the third doped group III nitride semiconductor is superimposed on the second doped group III nitride semiconductor; The doping types of the first semiconductor layer, the second semiconductor layer, the first doped III-nitride semiconductor and the third doped III-nitride semiconductor are all the first doping type; the doping type of the second doped III-nitride semiconductor is the second doping type; the second doped III-nitride semiconductor and the third doped III-nitride semiconductor in contact therewith form a tunnel junction.

7. The visible light band photonic crystal surface emitting laser according to claim 2, characterized in that: The columnar structure array further includes a third doped group III nitride semiconductor; the third doped group III nitride semiconductor is superimposed below the first doped group III nitride semiconductor; The doping types of the first semiconductor layer, the second semiconductor layer, the second doped III-nitride semiconductor and the third doped III-nitride semiconductor are all the first doping type; the doping type of the first doped III-nitride semiconductor is the second doping type; the third doped III-nitride semiconductor and the first doped III-nitride semiconductor in contact therewith form a tunnel junction.

8. The visible light band photonic crystal surface emitting laser according to claim 1, characterized in that: The visible light band photonic crystal surface emitting laser further comprises a first electrode and a second electrode; The first electrode contacts an upper surface of the first semiconductor layer; and the second electrode contacts an upper surface of the second semiconductor layer.

9. A method for preparing a visible light band photonic crystal surface emitting laser, characterized in that: The preparation method comprises: Selecting a substrate, and sequentially epitaxially growing an unintentionally doped layer and a doped semiconductor layer on the upper surface of the substrate; A columnar array is etched downward on the upper surface of the doped semiconductor layer, and a multi-layer structure is epitaxially grown upward from the etched portion of the upper layer in the doped semiconductor layer to form a columnar structure array; a first semiconductor layer is formed from the unetched portion of the lower layer in the doped semiconductor layer; wherein, when growing the uppermost layer of the columnar structure array, the tops of the columnar structures in the columnar structure array are contacted with each other by increasing the lateral growth rate, so that the upper surface of the columnar structure array forms a seamless plane; A second semiconductor layer is epitaxially grown upward on the gap-free plane.

10. The preparation method according to claim 9, characterized in that: Ways to increase the lateral growth rate include: When the uppermost part of the columnar structure is grown by a metal organic chemical vapor deposition process, the lateral growth rate is increased by increasing the growth temperature, ammonia flow rate and Ga precursor flow rate; or when the uppermost part of the columnar structure is grown by a molecular beam epitaxy process, the lateral growth rate is increased by increasing the Ga beam flow, nitrogen flow rate, nitrogen plasma source power, etc.

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