CN116316063A - Gallium nitride-based photonic crystal surface-emitting blue laser and preparation method thereof - Google Patents
Gallium nitride-based photonic crystal surface-emitting blue laser and preparation method thereof Download PDFInfo
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18308—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement
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- H01S5/00—Semiconductor lasers
- H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
- H01S5/042—Electrical excitation ; Circuits therefor
- H01S5/0425—Electrodes, e.g. characterised by the structure
- H01S5/04256—Electrodes, e.g. characterised by the structure characterised by the configuration
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- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/34333—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser
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Abstract
The invention discloses a gallium nitride-based photonic crystal surface-emitting blue laser and a preparation method thereof, wherein the structure comprises the following steps: the GaN-based semiconductor device comprises a substrate layer, a bottom GaN layer, a porous GaN layer, an AlGaN-n layer, an n electrode, a GaN/InGaN paired multi-layer quantum well active layer, an AlGaN-p barrier layer, a GaN-p layer, a p electrode and a photonic crystal layer. The invention provides a novel GaN-PCSEL which utilizes porous GaN with low and controllable refractive index as a coating layer, combines a surface etching type photonic crystal structure and an optimized layer structure design, can realize that an active layer and a surface photonic crystal layer have higher resonant light field coupling strength at the same time, and is beneficial to realizing low-threshold, high-efficiency and high-performance light excitation.
Description
Technical Field
The invention discloses a gallium nitride-based photonic crystal surface-emitting blue laser and a preparation method thereof, and belongs to the field of active photonic devices.
Background
A photonic crystal surface-emitting laser (PCSEL) is a semiconductor laser with great potential, which uses optical feedback in a two-dimensional plane of a photonic crystal band edge to perform resonance, optical gain and lasing, and a resonant cavity can cover the whole photonic crystal structure, so that a formed standing wave oscillates in the photonic crystal and is easy to efficiently couple gain with an active layer. The photonic crystal surface emitting laser has the advantages of large emitting area, simple structure, good single-mode property, low divergence angle, low absorption loss, low series resistance, high power output and the like, and has extremely wide application prospect and huge market value in the fields of high-density optical storage, information transmission, micro projector light source, biomedical sensing, laser radar LiDAR, laser solid-state lighting and the like.
The gallium nitride (GaN) -based III-V material can flexibly and adjustably cover any wave band from ultraviolet to green light, and has the unique advantages in terms of manufacturing microwave and millimeter wave devices, ultraviolet photodetectors, short-wavelength visible light emitting diodes and lasers by virtue of the advantages of large forbidden bandwidth, high breakdown voltage, high saturated electron drift rate, high thermal conductance and the like. The ultraviolet/blue/green light laser based on GaN material has wide application in the fields of high-speed communication, display system, high-density memory and the like and can realize excellent performance and application prospect.
However, gallium nitride-based PCSEL is limited by material growth, alGaN with relatively high refractive index has been used as a cladding layer, and thus, the reported electric pump gallium nitride-based PCSEL is to make buried air holes inside GaN material to form Photonic Crystals (PC) so as to obtain sufficient light field distribution intensity. The method has complex process, high difficulty and high cost, and the coupling strength of the optical field and the PC area and the active area can be limited. In addition, the PCSEL which is reported to obtain the photonic crystal from the surface GaN and is carved through the active quantum well layer at present can only stay on the optical pump for excitation, and damage is generated on the active layer, so that the quantum efficiency is low. These limit the breakthroughs of high performance blue lasers.
Disclosure of Invention
Aiming at the defects in the background technology, the invention provides a gallium nitride-based photonic crystal surface-emitting blue laser and a preparation method thereof, and the surface etching type PC structure and the optimized layer structure design are beneficial to realizing the low-threshold, high-efficiency and high-performance light excitation.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: a gallium nitride-based photonic crystal surface-emitting blue laser, comprising:
the substrate layer is a sapphire substrate or a silicon substrate;
the bottom GaN layer is positioned on the substrate layer;
the porous GaN layer is positioned on the bottom GaN layer, and the refractive index of the porous GaN layer is 1.6-2.2;
an AlGaN-n layer located over the porous GaN layer;
the quantum well active layer is positioned on the AlGaN-n layer;
the AlGaN-p barrier layer is positioned on the quantum well active layer;
a GaN-p layer located on the AlGaN-p barrier layer;
etching a photonic crystal layer of periodic holes with a certain depth on the surface of the GaN-p layer;
the refractive index of the porous GaN layer is smaller than that of other bottom GaN layers, alGaN-n layers, quantum well active layers, alGaN-p barrier layers and GaN-p layers;
a p electrode located on the surface of the GaN-p layer;
an n-electrode positioned on the surface of the AlGaN-n layer;
the p-type islands are formed from top-down etching of the GaN-p layer to the AlGaN-n layer.
Further, the thickness of the bottom GaN layer is 1500-50000 nm, and the refractive index is 2.4-2.49.
Further, the thickness of the porous GaN layer is 500-10000 nm, and the refractive index of the porous GaN layer is 1.6-2.2.
Further, the thickness of the AlGaN-n layer is 100-200 nm, and the refractive index is 2.4-2.49.
Further, the quantum well active layer is a 3-12 quantum well layer composed of InGaN/GaN pairs, and each quantum well layer comprises: the InGaN well layer is 2.5nm and the GaN barrier layer is 12nm, wherein the refractive index of the InGaN layer is 2.55-2.65, and the refractive index of the GaN barrier layer is 2.4-2.49.
Further, the AlGaN-p barrier layer has a thickness of 20nm and a refractive index of 2.3-2.4, wherein the Al content is 20%.
Further, the thickness of the GaN-p layer is 50-500 nm, and the refractive index is 2.4-2.49.
Further, the photonic crystal layer lattice type is triangular lattice or tetragonal lattice or honeycomb lattice, the etching depth is 30-400 nm, the period is 150-250 nm, and the pore radius is 10-100 nm.
Further, the p-electrode includes: ohmic contact metal electrode or metal electrode and ITO composite electrode; the n-electrode includes: ohmic contact to the metal electrode.
The preparation method of the photonic crystal surface emitting laser based on the porous gallium nitride coating layer comprises the following steps:
step 1: epitaxially growing a GaN-based III-V material on a sapphire substrate or a silicon substrate, wherein a bottom GaN layer, a heavily doped GaN-n layer, an AlGaN-n layer, a quantum well active layer, an AlGaN-p barrier layer and a GaN-p layer are sequentially arranged on the substrate;
step 2: preparing a photonic crystal mask layer by Electron Beam Lithography (EBL), then performing dry etching to form a hole, and removing the mask layer to form a photonic crystal layer;
step 3: performing photoetching, medium protection and electrochemical corrosion processes to change the heavily doped GaN-n layer into a porous GaN layer;
step 4: preparing a p electrode by photoetching, and a lift-off process;
step 5: photoetching, namely defining a photoetching window, and carrying out dry etching until the AlGaN-n layer is etched to form a mesa;
step 6: the n-electrode was prepared by photolithography, lift-off process.
The working principle is as follows: when the frequency of light emitted by the active layer (MQWs layer) meets the band gap condition of the energy band gamma point of the photonic crystal, the wavelength resonates in the plane of the photonic crystal to generate a standing wave, the resonance of the standing wave in the plane can interact with the active layer to form gain and particle number inversion, so that laser is generated, and meanwhile, the out-of-plane vertical emission of the laser is realized due to the first-order Bragg diffraction of the photonic crystal.
Advantageous effects
1. The invention uses the porous GaN with low refractive index as the coating layer, so that the optical field is more limited in the area above the porous GaN, more optical fields can be distributed in the active area and the photonic crystal area by utilizing the regulation and control of the refractive index of the porous GaN, the active layer and the surface type photonic crystal layer can have higher resonant optical field coupling strength, and the invention is favorable for realizing low-threshold, high-efficiency and high-performance light excitation.
2. The invention adopts the method of directly etching the GaN-p layer on the surface to form the photonic crystal structure, thereby reducing the difficulty and cost of the preparation process and being beneficial to realizing high-quality photonic crystals; compared with a structure with air holes buried in a GaN layer, the surface etching PC structure does not need a complex process of 'growth-etching-hole protection-regrowth'. The high temperature regrowth after etching can lead to low quality interfaces, thereby introducing unnecessary non-radiative recombination, and the interface resistance of secondary growth can be very large, affecting the device performance.
3. Compared with etching GaN quantum well penetration type PhC, the method does not introduce any defects into a III-V group active material system, does not influence the luminescence of the quantum well and the uniformity of current injection and distribution, and finally reduces the IQE of the device due to the defects introduced into the quantum well by etching.
Drawings
FIG. 1 is a side elevational view of the structure of the present invention;
fig. 2 is a flow chart of the preparation process of the present invention.
Description of the embodiments
The implementation of the technical solution is described in further detail below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
The invention is characterized in that: the porous GaN with low refractive index and controllable refractive index is used as a coating layer, and the high coupling strength of the optical field in the active layer and the photonic crystal layer is realized simultaneously by combining the surface etching type PC structure and the special layer structure design.
An embodiment as shown in fig. 1: the embodiment provides a photonic crystal surface-emitting blue laser structure based on a porous gallium nitride coating layer, which comprises:
a substrate layer;
the bottom GaN layer is positioned on the substrate layer;
the porous GaN layer is positioned on the bottom GaN layer;
an AlGaN-n layer located over the porous GaN layer;
the quantum well active layer is positioned on the AlGaN-n layer;
the AlGaN-p barrier layer is positioned on the quantum well active layer;
a GaN-p layer located on the AlGaN-p barrier layer;
a photonic crystal layer located over the GaN-p layer;
a p-electrode located on the surface of the GaN-p layer;
an n-electrode positioned on the surface of the AlGaN-n layer;
etching depth of the GaN-p layer into photonic crystal is 100nm; the photonic crystal layer has a triangular lattice type, a period of 216nm and a pore radius of 60nm.
The thickness of the underlying GaN layer was 1500nm and the refractive index was 2.46.
The thickness of the porous GaN layer was 1000nm and the refractive index was 1.7.
The AlGaN-n layer had a thickness of 200nm and a refractive index of 2.46.
The quantum well active layer is a 5-layer quantum well layer formed by InGaN2.5nm/GaN12nm pairwise, wherein the refractive index of the InGaN layer is 2.62, and the content of in is as follows: 10% of GaN barrier layer refractive index is 2.46.
The AlGaN-p barrier layer had a thickness of 20nm and a refractive index of 2.36, with an Al content of 20%.
The GaN-p layer had a thickness of 200nm and a refractive index of 2.46.
Under this parameter, a resonant wavelength of 451.043nm, a quality factor Q of 18277, a photonic crystal layer confinement factor ΓPhC of 4%, an active region confinement factor Γact of 20% and a confinement factor improvement of about 30% and 50% respectively compared with the prior art are obtained.
The preparation process steps of this example are as follows:
step 1: and epitaxially growing a GaN-based III-V material on the sapphire substrate, wherein a bottom layer GaN, a heavily doped GaN-n layer, an AlGaN-n layer, a quantum well active layer, an AlGaN-p barrier layer and a GaN-p layer are sequentially arranged on the substrate.
Step 2: and spin-coating PMMA, preparing a photonic crystal mask layer by Electron Beam Lithography (EBL), performing dry etching to form a hole, removing the mask layer to form the photonic crystal layer, wherein the target etching depth is 100 nm.
Step 3: and performing photoetching, medium protection and electrochemical corrosion processes to change the heavily doped GaN-n layer into a porous GaN layer.
Step 4: spin-coating 5 mu m thick photoresist on the front surface, pre-baking at 90 ℃ for 3min, performing UV exposure by using a mask plate with a certain pattern as a mask, developing to expose a specific area of a metal electrode to be deposited with p-type gallium nitride, and drying; sputtering Ni/Au two layers of metal with a certain thickness, stripping photoresist and metal on the photoresist by lift-off, and finally leaving a metal electrode with a thickness of 100nm in a specific area; and (5) drying.
Step 5: photoetching, namely defining a photoetching window, and carrying out dry etching until the AlGaN-n layer is formed, so as to form a mesa with the length and the width of 300 mu m.
Step 6: spin-coating 8 mu m thick photoresist, baking the photoresist, performing alignment with the photoetching in the previous step, developing to expose a specific area where an n electrode is to be deposited, and baking; sputtering Ni/Au two layers of metal with a certain thickness, stripping photoresist and metal on the photoresist by lift-off, and finally leaving a metal electrode with a thickness of 100nm in a specific area; and (5) drying.
Examples
The present embodiment provides: the manufacturing method of the photonic crystal surface-emitting blue laser based on the porous gallium nitride coating layer comprises the following steps:
a substrate layer;
the bottom GaN layer is positioned on the substrate layer;
the porous GaN layer is positioned on the bottom GaN layer;
an AlGaN-n layer located over the porous GaN layer;
the quantum well active layer is positioned on the AlGaN-n layer;
the AlGaN-p barrier layer is positioned on the quantum well active layer;
a GaN-p layer located on the AlGaN-p barrier layer;
a photonic crystal layer located over the GaN-p layer;
a p-electrode located on the surface of the GaN-p layer;
an n-electrode positioned on the surface of the AlGaN-n layer;
etching depth of the GaN-p layer into photonic crystal is 200nm; the photonic crystal layer has a tetragonal lattice type, a period of 216nm and a pore radius of 50nm.
The thickness of the underlying GaN layer was 1500nm and the refractive index was 2.46.
The thickness of the porous GaN layer was 1000nm and the refractive index was 1.9.
The AlGaN-n layer had a thickness of 100nm and a refractive index of 2.46.
The quantum well active layer is a 5-layer quantum well layer formed by InGaN2.5nm/GaN12nm pairwise, wherein the refractive index of the InGaN layer is 2.62, and the content of in is as follows: 10% of GaN barrier layer refractive index is 2.46.
The AlGaN-p barrier layer had a thickness of 20nm and a refractive index of 2.36, with an Al content of 20%.
The GaN-p layer had a thickness of 300nm and a refractive index of 2.46.
Under this parameter, a resonant wavelength of 450.766nm, a quality factor Q of 16714, a photonic crystal layer confinement factor ΓPhC of 3.9%, and an active region confinement factor Γact of 24% were obtained.
The preparation process of the second embodiment comprises the following steps:
step 1: and epitaxially growing a GaN-based III-V material on the silicon substrate, wherein a lattice matching transition layer, a bottom GaN layer, a heavily doped GaN-n layer, an AlGaN-n layer, a quantum well active layer, an AlGaN-p barrier layer and a GaN-p layer are sequentially arranged on the substrate.
Step 2: and spin-coating photoresist with a thickness of 1 μm, preparing a photonic crystal mask layer by Electron Beam Lithography (EBL), performing dry etching to form a hole, removing the mask layer to form the photonic crystal layer, wherein the target depth is 200 nm.
Step 3: and performing photoetching, medium protection and electrochemical corrosion processes to change the heavily doped GaN-n layer into a porous GaN layer.
Step 4: spin-coating 8 mu m thick photoresist on the front surface, pre-baking at 90 ℃ for 3min, performing UV exposure by using a mask plate with a certain pattern as a mask, developing to expose a specific area of a metal electrode to be deposited with p-type gallium nitride, and drying; sputtering Ni/Au two layers of metal with a certain thickness, stripping photoresist and metal on the photoresist by lift-off, and finally leaving a metal electrode with a thickness of 80nm in a specific area; and (5) drying.
Step 5: photoetching, namely defining a photoetching window, and carrying out dry etching until the AlGaN-n layer is formed, so as to form a mesa with the length and the width of 400 mu m.
Step 6: spin-coating 8 mu m thick photoresist, baking the photoresist, performing alignment with the photoetching in the previous step, developing to expose a specific area where an n electrode is to be deposited, and baking; sputtering Ti/Al/Ni/Au two layers of metal with a certain thickness, stripping photoresist and metal on the photoresist by lift-off, and finally leaving a metal electrode with a thickness of 80nm in a specific area; and (5) drying.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications and variations could be made by those skilled in the art without departing from the technical principles of the present invention, and such modifications and variations should also be regarded as being within the scope of the invention.
Claims (10)
1. A gallium nitride-based photonic crystal surface-emitting blue laser, comprising:
a substrate layer;
the bottom GaN layer is positioned on the substrate layer;
the porous GaN layer is positioned on the bottom GaN layer;
an AlGaN-n layer located over the porous GaN layer;
the quantum well active layer is positioned on the AlGaN-n layer;
the AlGaN-p barrier layer is positioned on the quantum well active layer;
a GaN-p layer located on the AlGaN-p barrier layer;
etching a photonic crystal layer of periodic holes with a certain depth on the surface of the GaN-p layer;
the refractive index of the porous GaN layer is smaller than that of other bottom GaN layers, alGaN-n layers, quantum well active layers, alGaN-p barrier layers and GaN-p layers;
a p electrode located on the surface of the GaN-p layer;
an n-electrode positioned on the surface of the AlGaN-n layer;
and forming square p-type islands from the GaN-p layer to the AlGaN-n layer from top to bottom.
2. The gallium nitride-based photonic crystal surface-emitting blue laser according to claim 1, wherein the thickness of the underlying GaN layer is 1500-50000 nm and the refractive index is 2.4-2.49.
3. The gallium nitride-based photonic crystal surface-emitting blue laser according to claim 1, wherein the thickness of the porous GaN layer is 500-10000 nm, and the refractive index thereof is 1.6-2.2.
4. The gallium nitride-based photonic crystal surface-emitting blue laser according to claim 1, wherein the AlGaN-n layer has a thickness of 100 to 200nm and a refractive index of 2.4 to 2.49.
5. The gallium nitride-based photonic crystal surface-emitting blue light laser according to claim 1, wherein the quantum well active layer is a 3-12 quantum well layer composed of InGaN/GaN pairs, each layer comprising: the InGaN well layer is 2.5nm and the GaN barrier layer is 12nm, wherein the refractive index of the InGaN layer is 2.55-2.65, and the refractive index of the GaN barrier layer is 2.4-2.49.
6. The gallium nitride-based photonic crystal surface-emitting blue laser according to claim 1, wherein the AlGaN-p blocking layer has a thickness of 20nm and a refractive index of 2.3 to 2.4, and the Al content is 20%.
7. The gallium nitride-based photonic crystal surface-emitting blue laser according to claim 1, wherein the GaN-p layer has a thickness of 50-500 nm and a refractive index of 2.4-2.49.
8. The gallium nitride-based photonic crystal surface-emitting blue light laser according to claim 1, wherein the photonic crystal layer lattice type is a triangular lattice, a square lattice or a honeycomb lattice, the etching depth is 30-400 nm, the period is 150-250 nm, and the pore radius is 10-100 nm.
9. A gallium nitride-based photonic crystal surface emitting blue laser according to claim 1, wherein said p-electrode comprises: ohmic contact metal electrode or metal electrode and ITO composite electrode; the n-electrode includes: ohmic contact to the metal electrode.
10. The preparation method of the photonic crystal surface emitting laser based on the porous gallium nitride coating layer is characterized by comprising the following steps of:
step 1: epitaxially growing a GaN-based III-V material on a sapphire substrate or a silicon substrate, wherein a bottom GaN layer, a heavily doped GaN-n layer, an AlGaN-n layer, a quantum well active layer, an AlGaN-p barrier layer and a GaN-p layer are sequentially arranged on the substrate;
step 2: preparing a photonic crystal mask layer by Electron Beam Lithography (EBL), then performing dry etching to form a hole, and removing the mask layer to form a photonic crystal layer;
step 3: performing photoetching, medium protection and electrochemical corrosion processes to change the heavily doped GaN-n layer into a porous GaN layer;
step 4: preparing a p electrode by photoetching, and a lift-off process;
step 5: photoetching, namely defining a photoetching window, and carrying out dry etching until the AlGaN-n layer is etched to form a mesa;
step 6: the n-electrode was prepared by photolithography, lift-off process.
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