Preparation method of epitaxial structure with micron holes and epitaxial structure
By growing a Si-doped 3D AlN layer on an AlN buffer layer and expanding the air gap using dry etching and electrochemical etching, the problem of total internal reflection between the AlN template and the sapphire substrate was solved, achieving efficient light extraction from deep ultraviolet LEDs and improving brightness.
Patent Information
- Application Number
- CN202511332501.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-18
- Publication Date
- 2025-12-12
AI Technical Summary
In the prior art, the refractive index difference between the AlN template and the sapphire substrate causes total internal reflection of photons at the interface, which reduces the light extraction efficiency of deep ultraviolet LEDs. Furthermore, large-scale air gaps are difficult to grow smoothly on the surface of the epitaxial layer, affecting the light extraction efficiency.
A Si-doped 3D AlN layer is grown on the surface of an AlN buffer layer. The nanoscale air gap is expanded to the micrometer scale through dry etching and electrochemical etching processes. By combining Si doping and controlled growth processes, a micrometer-sized porous structure with good conductivity is formed.
It significantly improves the light extraction efficiency of deep ultraviolet LEDs and enhances luminous brightness, especially with a brightness increase of approximately 32% within the ±37° range.
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Figure CN121126979A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of epitaxial wafer fabrication technology, and more particularly to a method for preparing an epitaxial structure with micron-sized holes and the epitaxial structure thereof, and further to a method for preparing an epitaxial structure with micron-sized holes for use in ultraviolet LEDs and the epitaxial structure thereof. Background Technology
[0002] Aluminum nitride (AlN) templates are the substrate materials for the epitaxial growth of aluminum gallium nitride-based deep ultraviolet LEDs (Light Emitting Diodes). The crystal quality of the AlN template directly determines the crystal quality of the upper aluminum gallium nitride layer. High-quality AlN templates can effectively reduce the through-dislocation density (TDDs) of aluminum gallium nitride, improve the radiative recombination efficiency of electrons and holes in the LED structure grown based on this material, and improve the reliability and lifespan of the LED.
[0003] However, when using a planar sapphire substrate to grow an AlN template, the large refractive index difference between sapphire and AlN causes some of the light emitted from the quantum well to undergo total internal reflection at the sapphire / AlN interface. Light with an incident angle greater than the total internal reflection angle cannot directly pass through the sapphire / AlN, resulting in low light extraction efficiency. Simultaneously, the large refractive index between sapphire and air also leads to total internal reflection, further reducing light extraction efficiency.
[0004] Introducing a 3D layer during AlN thin film growth allows for the creation of air gaps of a certain scale by controlling the growth conditions. These air gaps range in width from 15-50 nm and length from 70-150 nm. However, for deep ultraviolet (DUV) emission in the 200-320 nm band, the improvement in light extraction efficiency is limited. To significantly improve the light extraction efficiency of DUV emission in this band, the size of the air gap needs to be on the same order of magnitude as the emission wavelength (200-320 nm), or even larger. However, using controlled 3D epitaxial layer growth processes to achieve large-scale air gaps results in an inability to achieve a smooth surface on the epitaxial layer due to the low migration rate of Al atoms, and the large air gaps cannot be filled. Summary of the Invention
[0005] To address the aforementioned technical problems, this invention provides a method for preparing an epitaxial structure with micron-sized pores and the epitaxial structure itself. The technical solution of this invention is as follows: In a first aspect, a method for preparing an epitaxial structure with micron-sized pores is provided, comprising: S1, An AlN buffer layer is grown on the substrate surface using a magnetron sputtering device; S2, the substrate with the AlN buffer layer is placed in the MOCVD equipment, and a Si-doped 3D AlN layer is grown on the surface of the AlN buffer layer. The Si-doped 3D AlN layer contains nanoscale air gaps. S3, High-temperature AlN layer is grown on the surface of Si-doped 3D AlN layer; S4, an n-type AlGaN layer, a multi-quantum-well active layer, an electron blocking layer, a p-type AlGaN layer, and a p-type GaN contact layer are sequentially grown on the surface of a high-temperature AlN layer; S5, using a dry etching process, the region corresponding to the n electrode in the epitaxial structure obtained in S4 is etched to the middle part of the Si-doped 3DAlN layer, exposing part of the nanoscale air gap. S6, SiO2 protective layers are grown on the surface of the p-type GaN contact layer and the vertical etched surface using a CVD device; S7 uses electrochemical etching to expand the size of nanoscale air gaps and prepare micron-scale air gaps; S8. A p-electrode metal layer is prepared on a p-type GaN contact layer, and an n-electrode metal layer is prepared on a micron-level air gap of a Si-doped 3D AlN layer to obtain an epitaxial structure with micron-sized holes.
[0006] Preferably, the growth process of the AlN buffer layer in S1 is as follows: the sputtering power of the magnetron sputtering equipment is 3300~4000W, the N2 flow rate is 70~95sccm, the Ar gas flow rate is 1~4sccm, and the temperature is 700~750℃.
[0007] Preferably, S2, during the growth of a Si-doped 3D AlN layer, includes: S21, in the MOCVD equipment, the flow rate of NH3 is 1~5 SLM, the flow rate of TMA1 is 200~300 μmol / min, the pressure is 45~60 torr, the temperature is 900~1100℃, and the flow rate of SiH4 is 1×10⁻⁶. -8 ~3×10 -7 The flow rate of H2 was 30~60 SLM, and the growth distance of the MOCVD equipment was 50~60 mm, forming a Si-doped 3D mid-temperature layer with nanoscale air gaps; S22, a high-temperature layer is grown in two dimensions on a Si-doped 3D intermediate-temperature layer to fill the air gaps in the Si-doped 3D intermediate-temperature layer. The growth process of the high-temperature layer is as follows: the flow rate of TMAl is 150~220umol / min, the pressure is 25~50torr, the temperature is 1150~1300℃, the flow rate of NH3 is 200-800sccm, the flow rate of H2 is 45~100SLM, and the growth distance of the MOCVD equipment is 30~50mm.
[0008] Preferably, the growth process of the high-temperature AlN layer in S3 is as follows: the flow rate of TMAl is 300~440umol / min, the pressure is 25~50torr, the temperature is 1130~1200℃, and the flow rate of H2 is 45~100SLM.
[0009] Preferably, in S4, The n-type AlGaN layer is an n-type Al x Ga 1-x The N-layer has an x value of 0.55–0.7. The growth process is as follows: temperature 1000–1100℃, pressure 40–80 torr, TMAl flow rate 260–300 μmol / min, TMGa flow rate 180–220 μmol / min, NH3 flow rate 4000–8000 sccm, and SiH4 flow rate 2.6 × 10⁻⁶. -8 ~2.6×10 -9 mol / min, pure H2 carrier gas, H2 flow rate of 30~80 SLM, growth time of 50~120 min, growth distance of 10~30 mm; The active layer of the multi-quantum well has 1 to 10 pairs of periods; the barrier layer has an Al composition of 0.6 to 0.75 and a thickness of 8 to 15 nm; the well layer has an Al composition of 0.49 to 0.54 and a thickness of 1.3 to 3 nm. The electron blocking layer is a multi-quantum well structure with 1 to 5 pairs of periods; the barrier layer has an Al composition of 0.7 to 0.8 and a thickness of 8 to 15 nm; the well layer has an Al composition of 0.53 to 0.6 and a thickness of 1.5 to 3.5 nm; or, the electron blocking layer is a single-layer structure with an Al composition of 0.7 to 0.9 and a thickness of 15 nm to 60 nm, and the Cp₂Mg doping concentration is 1 × 10⁻⁶. 17 ~1×10 18 cm -3 ; The p-type AlGaN layer was grown for 100–300 s, with an Al composition of 0.3–0.6 and a Mg doping concentration of 1 × 10⁻⁶. 18 ~1×10 20 cm -3 The growth process is as follows: temperature is 900~1000℃, pressure is 60~100 torr, flow rate of TMAl is 180~210umol / min, flow rate of TMGa is 50~80umol / min, flow rate of NH3 is 2000~8000sccm, flow rate of Cp2Mg is 200~600sccm, and pure H2 carrier gas is used with a flow rate of 30~80SLM. The growth time of the p-type GaN contact layer is 100~500s, and the Mg doping concentration is 1×10⁻⁶. 19~1×10 21 cm -3 The growth process is as follows: temperature is 800℃~950℃, pressure is 100~300 torr, flow rate of TMGa is 30~60umol / min, flow rate of NH3 is 6000~20000sccm, flow rate of Cp2Mg is 400~800sccm, and pure H2 carrier gas is used with a flow rate of 10~30SLM.
[0010] Preferably, the dry etching process in S5 is as follows: a mixed gas of Cl2 and BCl3 is used, with a Cl2 gas flow rate of 20-40 sccm, a BCl3 gas flow rate of 5-10 sccm, a chamber pressure of 5-20 mTorr, an ICP power of 500-1000W, an RF bias power of 50-200W, an ICP frequency of 13.56MHz, an RF bias frequency of 2MHz, and an etching time of 1-10 min; after etching, O2 plasma resist removal and dilute hydrochloric acid cleaning are performed.
[0011] Preferably, in the S6 process of growing the SiO2 protective layer, the reaction gases are selected as SiH4 and N2O, the flow rate of SiH4 is 10-60 sccm, the flow rate of N2O is 1500-3500 sccm, the temperature is 600-800℃, the pressure is 0.1-1 torr, and the deposition rate is 10-50 nm / min.
[0012] Preferably, in step S7, during electrochemical etching, an In electrode is first coated onto the air gap layer at the edge of the Si-doped 3D AlN layer and connected to a Pt electrode. Then, the Pt electrode is connected to the positive terminal of the power supply, and another Pt electrode is connected to the negative terminal of the power supply. The epitaxial structure and the Pt electrode obtained in step S6 are completely immersed in a KOH electrolyte with a concentration of 5-15 wt%, and the KOH electrolyte is heated to 60-80°C, the voltage is 25-60V, and the etching time is 5-30 minutes.
[0013] Preferably, the O2 plasma degumming and dilute hydrochloric acid cleaning process is as follows: the flow rate of Ar gas is 500-2000 sccm, the flow rate of O2 is 200-1000 sccm, the mass ratio of hydrochloric acid to water is 1:10, and the time is 5-20 min.
[0014] In a second aspect, an epitaxial structure with micron-sized holes is provided, which is prepared by the method for preparing an epitaxial structure with micron-sized holes as described in the first aspect.
[0015] All of the above-mentioned optional technical solutions can be combined arbitrarily, and the present invention will not provide a detailed description of the structure after each combination.
[0016] By means of the above solution, the beneficial effects of the present invention are as follows: By growing a Si-doped 3D AlN layer with nanoscale air gaps on the surface of an AlN buffer layer, a Si-doped 3D AlN layer with conductive properties and n-polarity containing nanoscale spindle-shaped air gaps was prepared. After the full structure was grown, dry etching and electrochemical etching processes were used to expand the nanoscale spindle-shaped air gaps to the micrometer scale, thereby improving the light extraction efficiency in the AlN template.
[0017] During the growth of Si-doped 3D AlN layers, Si doping improves the conductivity of the Si-doped 3D AlN layers. By first growing a Si-doped 3D intermediate-temperature layer and then growing a high-temperature layer, the growth of nanoscale air gaps in the Si-doped 3D AlN layers can be achieved while ensuring that the surface of the Si-doped 3D AlN layers can be filled and flat.
[0018] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description
[0019] Figure 1 This is a flowchart of the method for preparing an epitaxial structure with micron-sized pores provided by the present invention.
[0020] Figure 2 This is a schematic diagram of the epitaxial structure formed by S1 to S4 in an embodiment of the present invention.
[0021] Figure 3 This is a schematic diagram of the epitaxial structure formed in S5 of this embodiment of the invention.
[0022] Figure 4 This is a schematic diagram of the epitaxial structure formed in S6 in an embodiment of the present invention.
[0023] Figure 5 This is a schematic diagram of electrochemical etching in an embodiment of the present invention.
[0024] Figure 6 This is a schematic diagram of the epitaxial structure with micron-sized pores prepared according to an embodiment of the present invention.
[0025] Figure 7 This is a schematic diagram comparing the light emission angles of LED chips with air gaps at the nanoscale and microscale. Detailed Implementation
[0026] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.
[0027] like Figure 1As shown, the method for preparing an epitaxial structure with micron-sized pores provided in this embodiment of the invention can be achieved through the following steps S1 to S8: S1, An AlN buffer layer 2 is grown on the surface of substrate 1 using a magnetron sputtering device.
[0028] The substrate 1 can be a sapphire substrate. The thickness of the AlN buffer layer 2 is 2~13nm.
[0029] In specific implementation, the growth process of the AlN buffer layer 2 in S1 is as follows: the sputtering power of the magnetron sputtering equipment is 3300~4000W, the N2 flow rate is 70~95 sccm (standard milliliters per minute), the Ar gas flow rate is 1~4 sccm, and the temperature is 700~750℃. The target material of the magnetron sputtering equipment is an Al target. The growth process of the AlN buffer layer 2 does not involve O2, the purpose of which is to prepare an n-polar AlN buffer layer 2, thereby improving the electrochemical etching rate of the subsequent Si-doped 3D AlN layer 3.
[0030] S2, the substrate 1 with the AlN buffer layer 2 is placed in an MOCVD (metal-organic chemical vapor deposition) device, and a Si-doped 3D AlN layer 3 is grown on the surface of the AlN buffer layer 2. The Si-doped 3D AlN layer 3 contains nanoscale air gaps.
[0031] In specific implementation, S2, during the growth of the Si-doped 3D AlN layer 3, includes: S21, in the MOCVD equipment, the flow rate of NH3 is 1~5 SLM (standard liters per minute), the flow rate of TMAl (trimethylaluminum) is 200~300 μmol / min, the pressure is 45~60 torr, the temperature is 900~1100℃, and the flow rate of SiH4 is 1×10⁻⁶. -8 ~3×10 -7 With an H2 flow rate of 30~60 SLM and a growth distance (thickness grown per unit time) of 50~60 mm in the MOCVD equipment, a Si-doped 3D mid-temperature layer containing nanoscale air gaps is formed. This process achieves three-dimensional growth at a relatively low temperature and a relatively high growth distance. The thickness of the Si-doped 3D mid-temperature layer is 200~450 nm.
[0032] S22 involves the two-dimensional growth of a high-temperature layer on a Si-doped 3D intermediate-temperature layer to fill the air gaps within the layer. The growth process for the high-temperature layer is as follows: TMAl flow rate of 150–220 μmol / min, pressure of 25–50 torr, temperature of 1150–1300 °C, NH3 flow rate of 200–800 sccm, H2 flow rate of 45–100 SLM, and a growth distance of 30–50 mm using the MOCVD equipment. The thickness of the high-temperature layer is 400–1000 nm. This process, combined with high temperature and a relatively short growth distance, enhances the migration ability of Al atoms, thereby achieving two-dimensional growth and ultimately filling the air gaps in the Si-doped 3D intermediate-temperature layer.
[0033] S3, a high-temperature AlN layer 4 is grown on the surface of the Si-doped 3D AlN layer 3.
[0034] In specific implementation, the growth process of the high-temperature AlN layer 4 in S3 is as follows: the flow rate of TMAl is 300~440umol / min, the pressure is 25~50torr, the temperature is 1130~1200℃, and the flow rate of H2 is 45~100SLM.
[0035] The main purpose of the high-temperature AlN layer 4 is to improve the surface smoothness of the Si-doped 3D AlN layer 3. The thickness of the high-temperature AlN layer 4 is 1000~1500nm.
[0036] S4, an n-type AlGaN layer 5, a multi-quantum-well active layer 6, an electron blocking layer 7, a p-type AlGaN layer 8, and a p-type GaN contact layer 9 are sequentially grown on the surface of the high-temperature AlN layer 4.
[0037] In specific implementation, in S4, the n-type AlGaN layer 5 is an n-type Al x Ga 1-x The N-layer has an x value of 0.55–0.7. The growth process is as follows: temperature 1000–1100℃, pressure 40–80 torr, TMAl flow rate 260–300 μmol / min, TMGa (trimethylgallium) flow rate 180–220 μmol / min, NH3 flow rate 4000–8000 sccm, and SiH4 flow rate 2.6 × 10⁻⁶. -8 ~2.6×10 -9 The growth rate was mol / min, with pure H2 carrier gas at a flow rate of 30-80 SLM, a growth time of 50-120 min, and a growth distance of 10-30 mm; the thickness of the n-type AlGaN layer 5 was 1.5-2.5 μm.
[0038] The active layer 6 of the multiple quantum wells has 1 to 10 pairs of periods; the barrier layer has an Al composition of 0.6 to 0.75 and a thickness of 8 to 15 nm; the well layer has an Al composition of 0.49 to 0.54 and a thickness of 1.3 to 3 nm.
[0039] The electron blocking layer 7 is a multi-quantum well structure with 1 to 5 pairs of periods; the barrier layer has an Al composition of 0.7 to 0.8 and a thickness of 8 to 15 nm; the well layer has an Al composition of 0.53 to 0.6 and a thickness of 1.5 to 3.5 nm; or, the electron blocking layer 7 is a single-layer structure with an Al composition of 0.7 to 0.9 and a thickness of 15 nm to 60 nm, and the Cp2Mg doping concentration (i.e., bis(cyclopentadienyl)magnesium) is 1 × 10⁻⁶. 17 ~1×10 18 cm -3 .
[0040] The growth time of the p-type AlGaN layer 8 is 100~300s, the Al composition is 0.3~0.6, and the Mg doping concentration is 1×10⁻⁶. 18 ~1×10 20 cm -3 The growth process is as follows: temperature is 900~1000℃, pressure is 60~100 torr, flow rate of TMAl is 180~210 μmol / min, flow rate of TMGa is 50~80 μmol / min, flow rate of NH3 is 2000~8000 sccm, flow rate of Cp2Mg is 200~600 sccm, pure H2 carrier gas is used, and the flow rate of H2 is 30~80 slm; the thickness of the p-type AlGaN layer 8 is 10~30 nm.
[0041] The growth time of the p-type GaN contact layer 9 is 100~500s, and the Mg doping concentration is 1×10⁻⁶. 19 ~1×10 21 cm -3 The growth process is as follows: temperature is 800℃~950℃, pressure is 100~300 torr, flow rate of TMGa is 30~60umol / min, flow rate of NH3 is 6000~20000sccm, flow rate of Cp2Mg is 400~800sccm, pure H2 carrier gas is used, and the flow rate of H2 is 10~30SLM; the thickness of p-type GaN contact layer 9 is 1~50nm.
[0042] The extensional structure formed up to this step is as follows: Figure 2 As shown.
[0043] S5 uses a dry etching process to etch the region corresponding to the n electrode in the epitaxial structure obtained in S4 to the middle part of the Si-doped 3DAlN layer 3, exposing part of the nanoscale air gap.
[0044] In specific implementation, the dry etching process in S5 is as follows: a mixed gas of Cl2 and BCl3 is used, with a Cl2 gas flow rate of 20-40 sccm, a BCl3 gas flow rate of 5-10 sccm, a chamber pressure of 5-20 mTorr, an ICP (inductively coupled plasma) power of 500-1000W, an RF (radio frequency) bias power of 50-200W, an ICP frequency of 13.56MHz, an RF bias frequency of 2MHz, and an etching time of 1-10 min; after etching, O2 plasma stripping and dilute hydrochloric acid cleaning are performed to remove residues.
[0045] In specific implementation, the O2 plasma degumming and dilute hydrochloric acid cleaning process is as follows: the flow rate of Ar gas is 500-2000 sccm, the flow rate of O2 is 200-1000 sccm, the mass ratio of hydrochloric acid to water is 1:10, and the time is 5-20 min.
[0046] The epitaxial structure formed through this step is as follows: Figure 3 As shown.
[0047] S6, SiO2 protective layer 10 is grown on the surface of p-type GaN contact layer 9 and the vertical etched surface using CVD (chemical vapor deposition) equipment.
[0048] In specific implementation, during the growth of the SiO2 protective layer 10 in step S6, the reaction gases are selected as SiH4 and N2O, the flow rate of SiH4 is 10-60 sccm, the flow rate of N2O is 1500-3500 sccm, the temperature is 600-800℃, the pressure is 0.1-1 torr, and the deposition rate is 10-50 nm / min; the thickness of the SiO2 protective layer 10 is 50-150 nm.
[0049] The epitaxial structure formed through this step is as follows: Figure 4 As shown.
[0050] S7 uses electrochemical etching to expand the size of nanoscale air gaps, thus creating micron-scale air gaps.
[0051] In specific implementation, during electrochemical etching in step S7, an In electrode 11 is first coated onto the air gap layer at the edge of the Si-doped 3D AlN layer 3 and connected to a Pt electrode 12. Then, the Pt electrode 12 is connected to the positive terminal of the power supply, and another Pt electrode 12 is connected to the negative terminal. The epitaxial structure obtained in step S6 and the Pt electrode 12 are then completely immersed in a 5-15 wt% KOH electrolyte solution. The KOH electrolyte solution is heated to 60-80°C, the voltage is 25-60V, and the etching time is 5-30 minutes. This process expands the size of the nano-scale air gap to the micrometer scale. A schematic diagram of the electrochemical etching is shown below. Figure 5 As shown.
[0052] S8, a p-electrode metal layer 13 is prepared on the p-type GaN contact layer 9, and an n-electrode metal layer 14 is prepared on the micron-level air gap of the Si-doped 3D AlN layer 3 to obtain an epitaxial structure with micron-sized holes.
[0053] In practice, this step involves coating, grinding, and scratching to prepare a surface on the epitaxial structure obtained in S7, such as... Figure 5 The LED chip shown has a p-electrode metal layer 13 made of NiAuNiAu (i.e., the p-electrode metal layer 13 consists of Ni, Au, Ni and Au layers from bottom to top) or NiAuNiRhTi (i.e., the p-electrode metal layer 13 consists of Ni, Au, Ni, Rh and Ti layers from bottom to top), and an n-electrode metal layer 14 made of CrAlTiAu (i.e., the n-electrode metal layer 14 consists of Cr, Al, Ti and Au layers from bottom to top) or CrTiAlNiAuTi (i.e., the n-electrode metal layer 14 consists of Cr, Ti, Al, Ni, Au and Ti layers from bottom to top).
[0054] Epitaxial structures with micron-sized pores, such as Figure 6 As shown. Figure 6 Compared to the Si-doped 3D AlN layer 3 Figure 2 In the Si-doped 3D AlN layer 3, the air gap scale is expanded from the nanometer level to the micrometer level.
[0055] like Figure 7 The diagram shown compares the emission angles of LED chips with nanoscale and microscale air gaps. Figure 7 As can be seen, compared with a 10mil*18mil chip with a nanoscale air gap, the chip brightness is improved in the range of -90° to 90° by using the method provided in the embodiments of the present invention, with the greatest brightness improvement at ±37°, which is approximately 32%.
[0056] Based on the above, this invention also provides an epitaxial structure with micron-sized holes, which is prepared using the method for preparing epitaxial structures with micron-sized holes described in the above embodiments. A schematic diagram of the prepared epitaxial structure with micron-sized holes is shown below. Figure 6 As shown.
[0057] The method for preparing an epitaxial structure with micron-sized pores provided in this invention has the following characteristics: 1. During the growth of Si-doped 3D AlN layer 3, Si heavy doping is performed to improve the conductivity of Si-doped 3D AlN layer 3. At the same time, by controlling the growth process of Si-doped 3D AlN layer 3 (first forming Si-doped 3D medium-temperature layer with low temperature, high NH3 flow rate and high growth distance, and then growing high-temperature layer with high temperature, low NH3 flow rate and low growth distance), the growth of nanoscale air gaps in Si-doped 3D AlN layer 3 is achieved, while ensuring that the surface of Si-doped 3D AlN layer 3 can be filled and flat.
[0058] 2. In the fabrication process, after the n electrode is etched to the Si-doped 3D AlN layer 3 (which has conductive properties and contains air gaps), the nanoscale air gaps are etched to the micrometer scale using an electrochemical etching process. The micrometer-scale air gaps will significantly increase the light propagation path, thereby improving the light extraction efficiency.
[0059] 3. By successively forming Si-doped 3D mid-temperature layer and high-temperature layer, the necessary conditions for preparing large-scale air gaps by electrochemical etching method are provided, which promotes the expansion of air gap size.
[0060] 4. By expanding the size of the nanoscale air gap through electrochemical etching, the size of the air gap is increased from the nanoscale to the microscale without affecting the quality and morphology of the grown epitaxial structure. This achieves the fabrication of microscale air gaps that cannot be achieved by directly controlling the epitaxial layer growth process.
[0061] 5. By rationally controlling the airflow process of sputtering the AlN buffer layer 2, combined with the process control of the Si-doped 3D AlN layer 3, and performing heavy Si doping, a Si-doped 3D AlN layer 3 with conductive properties and n-polarity containing nanoscale spindle-shaped air gaps was prepared. After the entire structure was grown, ICP etching and electrochemical etching processes were used to expand the nanoscale spindle-shaped air gaps to the micrometer scale, improving the light extraction efficiency in the AlN template. The n-polarity AlN buffer layer 2 prepared by sputtering can improve the electrochemical etching rate, and the Si-doped Si-doped 3D AlN layer 3 can improve both conductivity and the electrochemical etching rate.
[0062] 6. The nanoscale spindle-shaped air gap increases the conductive area and also improves the electrochemical etching rate. It combines the multiple enhancements of n-polarity, heavy Si doping, and nanoscale air gaps to improve the etching rate of Si-doped 3D AlN layer 3. It can effectively expand the scale of the nanoscale air gap, so that the size of the air gap reaches the same order of magnitude as the emission wavelength, which greatly improves the light extraction efficiency.
[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing an epitaxial structure with micron-sized pores, characterized in that, include: S1, An AlN buffer layer (2) is grown on the surface of a substrate (1) using a magnetron sputtering device. S2, the substrate (1) with the AlN buffer layer (2) is placed in the MOCVD equipment, and a Si-doped 3D AlN layer (3) is grown on the surface of the AlN buffer layer (2), wherein the Si-doped 3D AlN layer (3) contains nanoscale air gaps; S3, a high-temperature AlN layer (4) is grown on the surface of the Si-doped 3D AlN layer (3). S4, n-type AlGaN layer (5), multi-quantum well active layer (6), electron blocking layer (7), p-type AlGaN layer (8) and p-type GaN contact layer (9) are sequentially grown on the surface of high-temperature AlN layer (4). S5, using a dry etching process, the region corresponding to the n electrode in the epitaxial structure obtained in S4 is etched to the middle part of the Si-doped 3D AlN layer (3), exposing part of the nanoscale air gap; S6, SiO2 protective layer (10) is grown on the surface of p-type GaN contact layer (9) and vertical etching surface using CVD equipment. S7 uses electrochemical etching to expand the size of nanoscale air gaps and prepare micron-scale air gaps; S8, a p-electrode metal layer (13) is prepared on the p-type GaN contact layer (9), and an n-electrode metal layer (14) is prepared on the micron-level air gap of the Si-doped 3D AlN layer (3) to obtain an epitaxial structure with micron-sized holes.
2. The method for preparing an epitaxial structure with micron-sized pores according to claim 1, characterized in that, The growth process of the AlN buffer layer (2) in S1 is as follows: the sputtering power of the magnetron sputtering equipment is 3300~4000W, the N2 flow rate is 70~95sccm, the Ar gas flow rate is 1~4sccm, and the temperature is 700~750℃.
3. The method for preparing an epitaxial structure with micron-sized pores according to claim 1, characterized in that, The S2 process, during the growth of a Si-doped 3D AlN layer (3), includes: S21, in the MOCVD equipment, the flow rate of NH3 is 1~5 SLM, the flow rate of TMA1 is 200~300 μmol / min, the pressure is 45~60 torr, the temperature is 900~1100℃, and the flow rate of SiH4 is 1×10⁻⁶. -8 ~3×10 -7 The flow rate of H2 was 30~60 SLM, and the growth distance of the MOCVD equipment was 50~60 mm, forming a Si-doped 3D mid-temperature layer with nanoscale air gaps; S22, a high-temperature layer is grown in two dimensions on a Si-doped 3D intermediate-temperature layer to fill the air gaps in the Si-doped 3D intermediate-temperature layer. The growth process of the high-temperature layer is as follows: the flow rate of TMAl is 150~220umol / min, the pressure is 25~50torr, the temperature is 1150~1300℃, the flow rate of NH3 is 200-800sccm, the flow rate of H2 is 45~100SLM, and the growth distance of the MOCVD equipment is 30~50mm.
4. The method for preparing an epitaxial structure with micron-sized pores according to claim 1, characterized in that, The growth process of the high-temperature AlN layer (4) in S3 is as follows: the flow rate of TMAl is 300~440umol / min, the pressure is 25~50torr, the temperature is 1130~1200℃, and the flow rate of H2 is 45~100SLM.
5. The method for preparing an epitaxial structure with micron-sized pores according to claim 1, characterized in that, In S4, The n-type AlGaN layer (5) is an n-type Al x Ga 1-x The N-layer has an x value of 0.55–0.
7. The growth process is as follows: temperature 1000–1100℃, pressure 40–80 torr, TMAl flow rate 260–300 μmol / min, TMGa flow rate 180–220 μmol / min, NH3 flow rate 4000–8000 sccm, and SiH4 flow rate 2.6 × 10⁻⁶. -8 ~2.6×10 -9 mol / min, pure H2 carrier gas, H2 flow rate of 30~80 SLM, growth time of 50~120 min, growth distance of 10~30 mm; The number of periods in the multi-quantum well active layer (6) is 1 to 10 pairs; the Al composition of the barrier layer is 0.6 to 0.75 and the thickness is 8 to 15 nm; the Al composition of the well layer is 0.49 to 0.54 and the thickness is 1.3 to 3 nm. The electron blocking layer (7) is a multi-quantum well structure with 1 to 5 pairs of periods; the Al composition of the barrier layer is 0.7 to 0.8, and the thickness is 8 to 15 nm; the Al composition of the well layer is 0.53 to 0.6, and the thickness is 1.5 to 3.5 nm; or, the electron blocking layer (7) is a single-layer structure with an Al composition of 0.7 to 0.9, a thickness of 15 nm to 60 nm, and a Cp2Mg doping concentration of 1 × 10⁻⁶. 17 ~1×10 18 cm -3 ; The growth time of the p-type AlGaN layer (8) is 100~300s, the Al composition is 0.3~0.6, and the Mg doping concentration is 1×10⁻⁶. 18 ~1×10 20 cm -3 The growth process is as follows: temperature is 900~1000℃, pressure is 60~100 torr, flow rate of TMAl is 180~210umol / min, flow rate of TMGa is 50~80umol / min, flow rate of NH3 is 2000~8000sccm, flow rate of Cp2Mg is 200~600sccm, and pure H2 carrier gas is used with a flow rate of 30~80SLM. The growth time of the p-type GaN contact layer (9) is 100~500s, and the doping concentration of Mg is 1×10⁻⁶. 19 ~1×10 21 cm -3 The growth process is as follows: temperature is 800℃~950℃, pressure is 100~300 torr, flow rate of TMGa is 30~60umol / min, flow rate of NH3 is 6000~20000sccm, flow rate of Cp2Mg is 400~800sccm, and pure H2 carrier gas is used with a flow rate of 10~30SLM.
6. The method for preparing an epitaxial structure with micron-sized pores according to claim 1, characterized in that, The dry etching process in S5 is as follows: a mixed gas of Cl2 and BCl3 is used, with a Cl2 gas flow rate of 20-40 sccm, a BCl3 gas flow rate of 5-10 sccm, a chamber pressure of 5-20 mTorr, an ICP power of 500-1000W, an RF bias power of 50-200W, an ICP frequency of 13.56MHz, an RF bias frequency of 2MHz, and an etching time of 1-10 min. After etching, O2 plasma is used for resist removal and dilute hydrochloric acid cleaning.
7. The method for preparing an epitaxial structure with micron-sized pores according to claim 1, characterized in that, When growing the SiO2 protective layer (10) in S6, the reaction gases are SiH4 and N2O. The flow rate of SiH4 is 10-60 sccm, the flow rate of N2O is 1500-3500 sccm, the temperature is 600-800℃, the pressure is 0.1-1 torr, and the deposition rate is 10-50 nm / min.
8. The method for preparing an epitaxial structure with micron-sized pores according to claim 1, characterized in that, In the electrochemical etching process described in S7, an In electrode (11) is first coated on the air gap layer at the edge of the Si-doped 3D AlN layer (3) and connected to a Pt electrode (12). Then, the Pt electrode (12) is connected to the positive terminal of the power supply, and another Pt electrode (12) is connected to the negative terminal of the power supply. The epitaxial structure obtained in S6 and the Pt electrode (12) are completely immersed in a KOH electrolyte with a concentration of 5-15wt%, and the KOH electrolyte is heated to 60-80℃, the voltage is 25-60V, and the etching time is 5-30min.
9. The method for preparing an epitaxial structure with micron-sized pores according to claim 6, characterized in that, The O2 plasma degumming and dilute hydrochloric acid cleaning process is as follows: the flow rate of Ar gas is 500-2000 sccm, the flow rate of O2 is 200-1000 sccm, the mass ratio of hydrochloric acid to water is 1:10, and the time is 5-20 min.
10. An epitaxial structure having a micron-sized aperture, characterized in that, It is prepared by the method for preparing the epitaxial structure with micron-sized holes as described in any one of claims 1-9.