Island-shaped indium gallium nitrogen epitaxial structure and preparation method thereof, Micro LED chip

Abstract

The present invention provides an island-shaped indium gallium nitrogen epitaxial structure and a preparation method thereof, and a Micro LED chip. The island generation layer grows at low temperature, and spontaneously generates three-dimensional island growth on the surface of the stress presetting layer, thereby ensuring that the subsequent multi-quantum well barrier layer inherits the morphology of the island generation layer to form a uniform micron-sized island structure; the micron-scale island growth is conducive to relaxing the strain in the high-In component InGaN, and improving the crystal quality of the red-yellow light InGaN quantum well layer with a high In component. In addition, since the thickness of the InGaN layer in each island structure of the multi-quantum well barrier layer gradually increases from the bottom of each island structure along the side wall to the top, the In component content gradually increases from the bottom of each island structure along the side wall to the top, forming a barrier for the lateral diffusion of carriers, thereby reducing the diffusion of carriers to the edge of the chip and reducing the sidewall effect in the Micro-LED. Compared with the selective epitaxial technology, there is no need to use a photolithography patterning process, which effectively reduces the difficulty of the process.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to an island-shaped indium gallium nitride epitaxial structure and a preparation method thereof, and a Micro LED chip. Background Art

[0002] At present, indium gallium nitride (InGaN)-based light-emitting diodes (LEDs) have achieved relatively high peak external quantum efficiencies in the blue and green light bands, respectively. Therefore, they have been widely used in the display and lighting fields. However, when the traditional InGaN epitaxial structure is used in the visible light communication field, there is a problem of too long carrier recombination lifetime, resulting in a small optical communication bandwidth; in red and yellow light InGaN-based LEDs, the defect density of InGaN quantum wells with high In components is too large, resulting in low luminous efficiency of red and yellow light LEDs; in emerging fields such as Micro-LED, there is a problem of too fast sidewall non-radiative recombination rate, resulting in a sharp decrease in the luminous efficiency of Micro-LEDs as the pixel size decreases.

[0003] In view of the above problems, two methods are currently used to optimize the InGaN quantum well structure: one is selective epitaxy, which first deposits a mask layer on the substrate or GaN layer, then photolithographs micron- or submicron-level openings on the mask layer, and directly grows independent and unconnected Micro-LED pixels in the openings of the mask layer. Since the technology of selective epitaxy can directly prepare Micro-LED pixels without etching, the sidewall effect of Micro-LED is reduced. However, selective epitaxy not only increases the complexity and cost of epitaxy, but also brings great difficulties to chip processes such as Micro-LED bonding and electrode production, and the feasibility of mass production is very low. The other is to grow InGaN quantum dot structures. For example, in the Chinese patent, an indium gallium nitride quantum dot and its preparation method and application (application number CN202110332519.X), light-emitting diodes are prepared by growing nanometer-sized InGaN quantum dots. Due to the small size and high density of quantum dots, there are a large number of gaps between high-density InGaN quantum dots, which leads to a reduction in the effective InGaN light-emitting volume. When driven by high current, the device efficiency is seriously reduced. At the same time, the high-density quantum dot interface may also introduce new defects that cannot be ignored, making it difficult to perform effective quality control. Summary of the invention

[0004] In order to overcome the above shortcomings, the present invention provides an island-shaped indium gallium nitride epitaxial structure and its preparation method, and a Micro-LED chip, which utilizes the low temperature of the bottom layer and the compressive stress of the stress pre-set layer to form an island-shaped generation layer that grows spontaneously into an island-shaped morphology, and the surface of the island-shaped InGaN / GaN quantum well barrier layer also inherits the island-shaped morphology to form a micron-sized island structure. Micron-sized island growth is conducive to relaxing the strain in the high-In component InGaN and improving the crystal quality of the high-In component InGaN layer; in addition, a V-shaped groove is formed between adjacent island structures, which can inhibit the lateral movement of carriers and reduce the diffusion of carriers to the sidewalls of the Micro-LED, thereby reducing the sidewall effect of the Micro-LED and improving the luminous efficiency of the Micro-LED.

[0005] The technical solution provided by the present invention is:

[0006] In one aspect, the present invention provides an island-shaped InGaN epitaxial structure, comprising:

[0007] An island-shaped indium gallium nitride epitaxial structure, comprising: a nucleation layer, an n-type GaN current expansion layer, a stress presetting layer, an island-shaped generation layer, an island-shaped multi-quantum well barrier layer and a p-type electron blocking layer, a p-type GaN current expansion layer, and a p-type ohmic contact layer, which are sequentially formed on the surface of a growth substrate;

[0008] The island generation layer is in an island growth mode during its growth process, and an island morphology is spontaneously formed on the surface;

[0009] The island-shaped multi-quantum well barrier layer inherits the island-shaped morphology of the surface of the island-shaped generating layer and grows, and has micron-sized island-shaped structures distributed on the surface, and there are V-shaped grooves opening upward between adjacent island-shaped structures.

[0010] On the other hand, the present invention provides a method for preparing an island-shaped InGaN epitaxial structure, comprising the following steps: sequentially growing a nucleation layer, an n-type GaN current spreading layer, a stress presetting layer, an island-shaped generating layer, an island-shaped multi-quantum well barrier layer, a p-type electron blocking layer, a p-type GaN current spreading layer, and a p-type ohmic contact layer on the surface of a growth substrate;

[0011] The island generation layer is in an island growth mode during its growth process, and an island morphology is spontaneously formed on the surface;

[0012] The island-shaped multi-quantum well barrier layer inherits the island-shaped morphology of the surface of the island-shaped generating layer and grows, and has micron-sized island-shaped structures distributed on the surface, and there are V-shaped grooves opening upward between adjacent island-shaped structures.

[0013] On the other hand, the present invention provides a Micro LED chip, wherein the Micro LED chip includes the above-mentioned island-shaped InGaN epitaxial structure.

[0014] The island-shaped indium gallium nitride epitaxial structure and its preparation method, and the Micro LED chip provided by the present invention are characterized in that the island-shaped generation layer grows at low temperature and spontaneously forms an island-shaped morphology on the surface of the stress pre-setting layer, thereby ensuring that the subsequent multi-quantum well barrier layer inherits the surface of the island-shaped generation layer to form a uniform micron-sized island structure. Micron-scale island growth is conducive to relaxing the strain in the high-In component InGaN and improving the crystal quality of the red-yellow light InGaN quantum well layer with a high In component; in addition, due to the grooves between each island structure of the multi-quantum well barrier layer, the thickness of the single-layer InGaN quantum well layer gradually increases from the bottom of each island structure along the side wall to the top, and the In component content gradually increases from the bottom of each island structure along the side wall to the top, forming a barrier for the lateral diffusion of carriers at the side wall position near the bottom of the island structure, thereby reducing the diffusion of carriers to the edge of the chip and reducing the sidewall effect in the Micro-LED. Compared with the selective epitaxial technology that achieves similar effects, there is no need to use a photolithography patterning process, which effectively reduces the difficulty of the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of an island-shaped InGaN epitaxial structure in one embodiment of the present invention;

[0016] Figure 2 An atomic force microscope image of an island-shaped multi-quantum well barrier layer in one embodiment of the present invention;

[0017] Figure 3 for Figure 1 A magnified schematic diagram of the InGaN quantum well layer at A in the middle;

[0018] Figure 4 A schematic diagram of the energy band structure of an island-shaped multi-quantum well barrier layer in one embodiment of the present invention;

[0019] Figure 5 Flow chart of preparing an island-shaped InGaN epitaxial structure in one embodiment of the present invention.

[0020] Reference numerals:

[0021] 1-growth substrate, 2-nucleation layer, 3-n-type GaN current spreading layer, 4-stress pre-setting layer, 5-island generation layer, 6-island multi-quantum well barrier layer, 61-InGaN quantum well layer, 7-p-type electron blocking layer, 8-p-type GaN current spreading layer, 9-p-type ohmic contact layer. DETAILED DESCRIPTION

[0022] In order to more clearly illustrate the implementation cases of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings and other implementation methods can be obtained based on these drawings without creative work.

[0023] The first embodiment of the present invention is an island-shaped indium gallium nitride epitaxial structure, comprising: a nucleation layer, an n-type GaN current spreading layer, a stress presetting layer, an island-shaped generation layer, an island-shaped multi-quantum well barrier layer and a p-type electron blocking layer, a p-type GaN current spreading layer, and a p-type ohmic contact layer sequentially formed on the surface of a growth substrate; the island-shaped generation layer is in an island-shaped growth mode during its growth, and an island-shaped morphology is spontaneously formed on the surface; the island-shaped multi-quantum well barrier layer grows by inheriting the island-shaped morphology on the surface of the island-shaped generation layer, and micron-sized island structures are distributed on the surface, and there are V-shaped grooves opening upward between adjacent island structures. Figure 1 As shown, the growth substrate 1 used in this embodiment includes but is not limited to a silicon substrate, a sapphire substrate, a GaN substrate, a silicon carbide substrate, etc.; the nucleation layer 2 is a stacked structure of 200nm AlN and AlGaN, and the Al content in the AlGaN gradually decreases as the distance from the substrate increases, which is beneficial to reducing the interface defects between the nucleation layer and the subsequently grown n-type GaN current extension layer. In one example, the AlGaN layer is an AlGaN layer with a thickness of 120nm at the bottom. 0.40 Ga 0.60 The N layer and its surface 150nm thick Al 0.20 Ga 0.80 N layer; the n-type GaN current spreading layer 3 is a GaN structure doped with Si, with a thickness of 2000nm and a Si doping concentration of 8×10 18 / cm 3 The stress pre-setting layer is n-type doped Al x Ga 1-x N layer, 0.05≦x≦0.3, growth temperature is 900℃-1000℃, pressure is 75torr-100torr, thickness is 10nm-30nm, in one example, stress pre-setting layer 4 is 15nm Al 0.20 Ga 0.80 In order to avoid the additional series resistance brought by this layer, the N layer is n-type doped during the growth process. In this embodiment, silane is used for n-type doping with a doping concentration of 2×10 18 / cm 3In other embodiments, other elements with a valence electron number greater than four, such as phosphorus (P), arsenic (As) or antimony (Sb), may be used to dope the stress pre-set layer, as long as the elements can introduce additional free electrons into the lattice after doping, thereby enhancing the conductivity of the semiconductor and reducing the resistance of the layer.

[0024] The island generation layer is composed of In y Ga 1-y N and In z Ga 1-z N / GaN superlattice layer, growth temperature is 550℃-750℃, 0.03≦y≦0.1, 0≦z≦0.8, among which, In y Ga 1-y The thickness of N is 5nm-20nm, In z Ga 1-z The total thickness of the N / GaN superlattice layer is 20nm-50nm. In one example, the island generation layer 5 is grown at a low temperature (550℃-750℃), the surface atomic mobility is reduced, and the surface spontaneously grows into an island morphology under the low temperature condition of 550℃-750℃ and the compressive stress of the stress presetting layer; in one example, the island generation layer is In grown at 600℃ 0.08 Ga 0.92 N layer and In 0.05 Ga 0.95 N / GaN superlattice layer: In 0.08 Ga 0.92 The thickness of N is 10nm. When it reaches the surface of the stress pre-stress layer during the growth process, it is subjected to compressive stress. Under the combined influence of lower mobility and compressive stress, the In 0.08 Ga 0.92 N is used to achieve the lowest surface free energy, resulting in an island growth mode, with a three-dimensional island morphology spontaneously formed on the surface; then In grown at 600°C 0.05 Ga 0.95 In within a single period of N / GaN superlattice layer 0.05 Ga 0.95 The thickness of N is 2nm, the subsequent GaN is 4nm, the number of cycles is 5 pairs, the total thickness is 30nm, covering In 0.08 Ga 0.92 The surface of the N layer continues the above island morphology. 0.08 Ga 0.92 N layer and In 0.05 Ga 0.95 The N / GaN superlattice layer also provides sufficient lattice relaxation preparation for the subsequent island-shaped multi-quantum well barrier layer.

[0025] The island-shaped multi-quantum well barrier layer 6 is In m Ga 1-mThe periodic structure of N / GaN has a period number of 1-10, where 0.1≦m≦0.4 and a single layer of In m Ga 1-m The thickness of N is greater than or equal to 2nm and less than or equal to 5nm, and the thickness of the single-layer GaN is greater than or equal to 3nm and less than or equal to 25nm; the growth temperature is 700℃-800℃, and the pressure is 75torr-100torr. In one example, the island-shaped multi-quantum well barrier layer is 5 pairs of In 0.28 Ga 0.72 N / GaN (2.5nm / 10nm) multi-quantum well barrier structure, emitting wavelength of 540nm; In 0.28 Ga 0.72 During the growth process of N quantum well, N2 was used as carrier gas at a temperature of 700°C, which was unintentional doping growth. During the growth process of GaN quantum barrier, the reaction chamber temperature was raised to 950°C, and silicon doping was used with a doping concentration of 3×10 17 / cm 3 The island-shaped multi-quantum well barrier layer grows on the surface of the formed island-shaped morphology, covering the side and upper surface of the island-shaped morphology. On the basis of the island-shaped morphology provided by the island-shaped generation layer, a uniformly distributed micron-sized island structure is further formed, such as Figure 2 As shown in the atomic force microscope image, the average lateral size of the island structure is 0.8μm-1.2μm. There are grooves between adjacent island structures (including grooves between two adjacent island structures or at the junction of multiple island structures). The grooves have a certain depth and gradually increase in width from the bottom to the top, showing a V-shaped opening upward. The opening width of the V-shaped groove (i.e., the width of the top of the groove) is 20nm-200nm, and the surface density is 1×10 8 / cm 2 Up to 2×10 8 / cm 2 The micron-scale island growth is beneficial to relax the strain in the high-In content InGaN and improve the crystal quality of the high-In content red-yellow light InGaN quantum well layer.

[0026] The non-radiative recombination of Micro-LED mainly occurs on the side walls of the InGaN quantum well layer; the side wall effect of InGaN-based green light Micro-LED (In enrichment leads to strong carrier localization) is much smaller than that of InGaN-based blue light Micro-LED. This phenomenon directly proves that the degree of carrier localization in the InGaN quantum well layer is closely related to the non-radiative recombination rate of the side wall. In each island structure grown in this embodiment, the island multi-quantum well barrier layer is a periodic structure of InGaN / GaN. On the original island morphology surface, that is, on the basis of the island morphology provided by the island generation layer, the thickness of each single-layer InGaN quantum well layer gradually increases in the longitudinal direction from the lowest position of each island structure along the side wall to the highest position of the top, and the In component content gradually increases from the lowest position of each island structure along the side wall to the highest position of the top (the side wall here refers to the surface between the lowest height and the highest point of each island structure; the thickness in the longitudinal direction refers to the distance in the longitudinal direction from the original island morphology surface before the InGaN layer is deposited to the upper surface after the InGaN quantum well layer is deposited); that is, the InGaN quantum well layer covers the island morphology surface of the preparation layer as a whole, but the thickness and In component content at different positions on the island morphology surface are different: Figure 3 As shown in the enlarged schematic diagram, before the InGaN layer is deposited, the original island morphology on the surface of the island generating layer 5 is a flat arc-shaped protrusion, and the thickness of the deposited InGaN quantum well layer 61 in the longitudinal direction changes with the position. The closer to the top of the island structure, the thicker the thickness and the higher the In component content. Compared with the thickness and In component content at different heights, the thickness h1 and In component content are the smallest at the bottom side wall of each island structure, and the thickness h2 and In component content at the top of the island structure are the largest.

[0027] Referring to the literature record (Tailored emission color synthesis using microfacetquantum wells consisting of nitride semiconductors without phosphors, M.Funato et al, Appl. Phys. Lett.88, 261920 (2006)), what is different from the present embodiment is that SiO2 is used as a mask for selective epitaxy in the literature, and the process is relatively more complicated. In addition, the cross-sectional view of the island structure of the bottom layer before InGaN is deposited is a whole, that is, the upper surface is not arc-shaped but flat; what is the same as the present embodiment is that on the island-shaped morphology surface of the bottom layer, affected by the diffusion rate of adsorbed atoms at different positions, the growth rate of the InGaN layer at the top is greater than the growth rate at the side wall, and gradually increases from 0.04nm / s at the bottom side wall to 0.15nm / s at the trapezoidal upper surface, and the growth rate along the side wall upward gradually increases, and for each island structure For the InGaN layer on the trapezoidal structure, the thickness of the InGaN layer at the top is greater than that at the side wall, and the thickness gradually increases along the side wall. At the same time, the In component content at the top is greater than that at the side wall, gradually increasing from 0.04 at the bottom side wall to 0.16 at the upper surface of the trapezoid, and the In component content gradually increases along the side wall. At the same time, it is detected that the energy level in the middle of the side wall is about 0.8 eV greater than the energy level at the upper surface of the trapezoid. Therefore, for each island structure, the energy level at the top will be relatively low, the energy level at the side wall will be higher, and the closer to the bottom of the island structure, the higher the energy level.

[0028] Similarly, in this embodiment, on the original island-shaped morphology surface, since the thickness of each island-shaped structure of the InGaN layer gradually increases upward along the side wall, and the In component content gradually increases, the energy level near the bottom of the side wall is greater than the energy level near the top. Therefore, a potential barrier is generated between adjacent island-shaped structures, which inhibits the lateral diffusion of carriers. Figure 4 As shown in the energy band, since there are barriers with higher energy levels between different island structures in the island-shaped multi-quantum well barrier layer 6, the diffusion of carriers (including electrons and holes) to the side walls is suppressed, making the carriers more inclined to move in the island structure and undergo radiative recombination, which can effectively prevent the carriers from diffusing to the side wall defects for non-radiative recombination.

[0029] The p-type electron blocking layer 7 is a Mg-doped AlGaN layer with a Mg doping concentration of 2×10 19 / cm 3 , with a thickness of 20 nm, and is grown along the surface of the island-shaped multi-quantum well barrier layer. The morphology of its upper surface is basically consistent with the surface of the island-shaped multi-quantum well barrier layer, and also presents a uniformly distributed island morphology.

[0030] The p-type GaN current spreading layer 8 is a Mg-doped GaN layer with a Mg doping concentration of 1×10 18 / cm 3 , with a thickness of 20nm, and is formed at a relatively small growth rate to promote the lateral growth of the GaN layer and form a planarized upper surface (i.e., the surface close to the p-type ohmic contact layer).

[0031] The p-type ohmic contact layer 9 is a highly doped GaN layer, which is also a Mg-doped GaN layer. However, the Mg doping concentration is greater than the doping concentration in the p-type GaN current spreading layer (for example, in one example, the Mg doping concentration in the p-type GaN current spreading layer 8 is 1×10 18 / cm 3 The Mg doping concentration in the P-type ohmic contact layer 9 is 3×10 20 / cm 3 , the doping concentration of Mg in the p-type ohmic contact layer 9 is 300 times that of the p-type GaN current spreading layer 8).

[0032] During the growth of the island-shaped InGaN epitaxial structure, Figure 5 As shown, first, a MOCVD growth device is used and a Si (111) substrate is selected as a growth substrate layer. In the MOCVD system, the growth substrate is subjected to high-temperature surface treatment to remove the oxide layer. Then, for different structures, the required precursor sources, gas sources and carrier gases are introduced at specific temperatures, including Ga source, Al source, In source, Mg, Si source and N source and N2, H2, Ar, etc. The Ga source in the following embodiment is trimethylgallium (TMG), the Al source is trimethylaluminum (TMAl), the In source is trimethylindium (TMIn), the Mg source is bis(cyclopentadienyl)magnesium (Cp2Mg), the Si source is silane (SiH4), the N source is ammonia (NH3), and the carrier gas is N2 and H2. A nucleation layer, an n-type GaN current spreading layer, a stress presetting layer, an island generation layer, an island multi-quantum well barrier layer, a p-type electron blocking layer, a p-type GaN current spreading layer, and a p-type ohmic contact layer are sequentially grown on the surface of the growth substrate.

[0033] The specific steps include:

[0034] 1. Place the Si(111) substrate in the MOCVD reaction chamber, heat it to 1100°C, and introduce H2 for 5 minutes of high-temperature surface treatment to remove the oxide layer and form clear atomic steps.

[0035] 2. Set the temperature of the reaction chamber to 1000℃-1100℃, introduce trimethylaluminum (TMAl) and ammonia (NH3) into the reaction chamber, and grow a 200nm thick AlN layer under the condition of H2 as carrier gas; then increase the flow rate of ammonia and introduce trimethylgallium (TMGa) to grow a 120nm thick AlN layer. 0.40 Ga 0.60 N layer, increase the flow rate of ammonia again and reduce the flow rate of trimethylaluminum (TMAl) to grow Al with a thickness of 150nm 0.20 Ga 0.80 N layer. The nucleation layer 2 is composed of AlN layer, Al 0.40 Ga 0.60 N layer and Al 0.20 Ga 0.80 It is composed of N layers.

[0036] 3. Using silane (SiH4) as a dopant, the growth temperature is 1050°C to grow an n-type GaN current spreading layer 3 with a thickness of 2000nm and a Si doping concentration of 8×10 18 / cm 3 .

[0037] 4. Set the reaction chamber temperature to 950℃-1000℃, use H2 as carrier gas, introduce trimethylaluminum (TMAl), ammonia (NH3), and trimethylgallium (TMGa) into the MOCVD reaction chamber, and grow Al with a thickness of 15nm. 0.20 Ga 0.80 N stress pre-layer, and n-type doping with silane, the doping concentration is 2×10 18 / cm 3 , introducing extra free electrons into the crystal lattice, which enhances the conductivity of the semiconductor and reduces the resistance of the layer.

[0038] 5. When growing the island-shaped generation layer, lower the temperature of the reaction chamber to 600°C and grow a 10nm In layer first. 0.08 Ga 0.92 N layers. 0.08 Ga 0.92 The N layer is exposed to Al 0.20 Ga 0.80 The compressive stress applied by the N stress pre-stress layer. Under the combined influence of lower mobility (low temperature) and compressive stress, the In 0.08 Ga 0.92 N exhibits an island growth mode with the lowest surface free energy, and a three-dimensional island morphology is spontaneously formed on the surface. Subsequently, In grown at 600℃ 0.05 Ga 0.95 In within a single period of N / GaN superlattice layer 0.05 Ga 0.95The thickness of N is 2nm, the subsequent GaN is 4nm, the number of cycles is 5 pairs, the total thickness is 30nm, covering In 0.08 Ga 0.92 The surface of the N layer continues the above island morphology. 0.08 Ga 0.92 N layer and In 0.05 Ga 0.95 The N / GaN superlattice layer also provides sufficient lattice relaxation preparation for the subsequent island-shaped multi-quantum well barrier layer.

[0039] 6. Using N2 as carrier gas, grow In at 700℃ 0.28 Ga 0.72 After the N quantum well, the temperature of the reaction chamber is raised to 950°C to grow GaN quantum barriers, In 0.28 Ga 0.72 The N quantum well is unintentionally doped, and the silicon doping concentration in the GaN quantum barrier is 3×10 17 / cm 3 , repeat and grow 5 pairs. Get 5 pairs of periodic long In 0.28 Ga 0.72 N / GaN multi-quantum well barrier layer structure, in which a single layer of In 0.28 Ga 0.72 The thickness of N is 2.5nm, and the thickness of a single-layer GaN in each period is 10nm. The emission wavelength of the multi-quantum well barrier layer is about 540nm, which belongs to the green light band. 0.28 Ga 0.72 The N / GaN multi-quantum well barrier layer inherits the island morphology of the island generation layer, forming a uniformly distributed micron-sized island structure, such as Figure 2 As shown in the atomic force microscope image, the average lateral size of the island structure is 0.8μm-1.2μm. There are grooves between adjacent island structures. The grooves have a certain depth and gradually increase in width from the bottom to the top, showing a V-shaped opening upward. The opening width of the V-shaped groove (i.e., the width of the top of the groove) is 20nm-200nm, and the surface density is 1×10 8 / cm 2 Up to 2×10 8 / cm 2 The micron-scale island growth is beneficial to relax the strain in the high-In content InGaN and improve the crystal quality of the high-In content red-yellow light InGaN quantum well layer.

[0040] 7. The growth temperature is between 800℃ and 900℃, N2 is used as the carrier gas, TMAl, TMGa, and NH3 are introduced, and Cp2Mg is used as the dopant to obtain a 20nm thick Mg doping concentration of 2.0×10 19 / cm 3 Al0.25 Ga 0.65 N serves as the p-type electron blocking layer 7, and the morphology of its upper surface is basically consistent with the surface of the island-shaped multi-quantum well barrier layer, and also presents a uniformly distributed island morphology.

[0041] 8. Using H2 and N2 as carrier gases, the growth temperature is 950℃-1000℃, the thickness is 80nm, and the Mg doping concentration is 1×10 18 / cm 3 The GaN layer is used as the p-type current spreading layer 8. Since this layer adopts a lower growth rate to promote the lateral growth and planarization of GaN, a planarized upper surface (i.e., the surface close to the p-type ohmic contact layer) is formed, so that the p-type GaN current spreading layer has a flat surface on the side close to the p-type ohmic contact layer.

[0042] 9. Using H2 or N2 as carrier gas, Cp2Mg as dopant, and epitaxial growth temperature of 900℃-1000℃, the Mg doping concentration of 3×10 20 / cm 3 A GaN layer with a thickness of 10 nm serves as the P-type ohmic contact layer 9 .

[0043] Another embodiment of the present invention is a Micro LED chip, wherein the Micro LED chip includes the above-mentioned island-shaped InGaN epitaxial structure. It should be understood that since the island-shaped generation layer in the island-shaped InGaN epitaxial structure in the Micro LED chip grows at a low temperature, an island-shaped morphology is spontaneously formed on the surface of the stress pre-set layer, thereby ensuring that the subsequent multi-quantum well barrier layer inherits the surface of the island-shaped generation layer to form a uniform micron-sized island structure. Micron-scale island growth is conducive to relaxing the strain in high-In component InGaN and improving the crystal quality of the red-yellow light InGaN quantum well layer with a high In component. In addition, due to the grooves between each island structure of the multi-quantum well barrier layer, on the bottom island morphology surface, the thickness of the single-layer InGaN quantum well layer gradually increases from the bottom of each island structure along the side wall to the top, and the In component content gradually increases from the bottom of each island structure along the side wall to the top, causing the overall energy level at the side wall of the island structure to be larger than the energy level at the top, forming a barrier for the lateral diffusion of carriers, making the carriers more inclined to move within the island structure for radiative recombination, thereby reducing the diffusion of carriers to the edge of the chip, effectively avoiding non-radiative recombination of carriers at defective chip edge positions, and reducing the sidewall effect in Micro-LED.

[0044] During the preparation of the Micro LED chip, the island-shaped InGaN epitaxial structure is etched into multiple pixel units; each pixel unit is formed with a first electrode and a second electrode, the first electrode is conductively connected to the n-type GaN current spreading layer in the pixel unit, and the second electrode is conductively connected to the p-type GaN current spreading layer in the pixel unit. The Micro LED chip in this embodiment contains a plurality of pixel units, which are prepared by using the above-mentioned island-shaped InGaN epitaxial structure. The size of the Micro LED is generally less than 50 μm according to a predetermined size. The specific size can be designed according to the actual application requirements. The preparation process includes using ICP dry etching technology to perform pixel etching on the island-shaped InGaN epitaxial structure, so that at least the multi-quantum well barrier layers between different pixel units are independent of each other, so as to form a pixel structure that can be driven independently. In addition, it also includes the preparation of a first electrode and a second electrode. The first electrode and the second electrode can be located on the same side of the pixel unit (forming an inverted structure) or on different sides of the pixel unit (forming a vertical structure or a normal structure). Regardless of how the positions of the first electrode and the second electrode are designed, it can be determined that the first electrode is conductively connected to the n-type GaN current expansion layer in the Micro LED chip, and the second electrode is conductively connected to the p-type GaN current expansion layer in the Micro LED chip. In this way, the external current is conducted to the Micro LED chip through the first electrode and the second electrode. Moreover, for a Micro LED chip in which each pixel unit can be driven independently, at least one of the first electrode or the second electrode is conductively connected independently to each pixel unit in the Micro LED chip. In addition, in other embodiments, a bonding layer, a reflective layer, a passivation layer, a connecting metal layer, a transparent conductive layer and other structures are formed in the Micro LED chip to enhance the light-emitting effect of the chip. This embodiment does not impose any restrictions on this, as long as the Micro LED chip can emit light normally.

[0045] It should be noted that the above embodiments can be freely combined as needed. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention.

Claims

1. An island-shaped indium gallium nitride epitaxial structure, characterized in that: include: A nucleation layer, an n-type GaN current spreading layer, a stress presetting layer, an island generation layer, an island multi-quantum well barrier layer, a p-type electron blocking layer, a p-type GaN current spreading layer, and a p-type ohmic contact layer are sequentially formed on the surface of the growth substrate; The island generation layer is in an island growth mode during its growth process, and an island morphology is spontaneously formed on the surface; The island-shaped multi-quantum well barrier layer inherits the island-shaped morphology of the surface of the island-shaped generating layer and grows, and has micron-sized island-shaped structures distributed on the surface, and there are V-shaped grooves with openings upward between adjacent island-shaped structures; The island-shaped multi-quantum well barrier layer is a periodic structure of InGaN / GaN. On the original island-shaped morphology surface, the thickness of each InGaN quantum well layer in the longitudinal direction gradually increases from the lowest position of each island structure along the side wall to the highest position of the top, and the In component content gradually increases from the lowest position of each island structure along the side wall to the highest position of the top.

2. The island-shaped InGaN epitaxial structure according to claim 1, characterized in that: The growth temperature of the island generating layer is 550° C.-750° C., and the surface spontaneously forms an island morphology under the low temperature condition of 550° C.-750° C. and the compressive stress of the stress presetting layer.

3. The island-shaped InGaN epitaxial structure according to claim 1, characterized in that: The stress presetting layer is n-type doped Al x Ga 1-x N layer, 0.05≦x≦0.3, growth temperature is 900℃-1000℃, pressure is 75torr-100torr, thickness is 10nm-30nm.

4. The island-shaped InGaN epitaxial structure according to claim 1, characterized in that: The island generation layer is composed of In y Ga 1-y N and In z Ga 1-z N / GaN superlattice layer composition, 0.03≦y≦0.1, 0≦z≦0.8, among which In y Ga 1-y The thickness of N is 5nm-20nm, In z Ga 1-z The total thickness of the N / GaN superlattice layer is 20nm-50nm.

5. The island-shaped InGaN epitaxial structure according to claim 1, characterized in that: The island structure in the island multi-quantum well barrier layer has an average lateral size of 0.8 μm-1.2 μm and a surface density of 1×10 8 / cm 2 Up to 2×10 8 / cm 2 The opening width of the V-groove between adjacent island structures is 20nm-200nm.

6. The island-shaped InGaN epitaxial structure according to claim 1, characterized in that: The island-shaped multi-quantum well barrier layer is In m Ga 1-m The periodic structure of N / GaN has a period number of 1-10, where 0.1≦m≦0.4 and a single layer of In m Ga 1-m The N thickness is greater than or equal to 2nm and less than or equal to 5nm, and the thickness of the single-layer GaN is greater than or equal to 3nm and less than or equal to 25nm; the growth temperature is 700℃-800℃, and the pressure is 75torr-100torr.

7. The island-shaped InGaN epitaxial structure according to claim 1, characterized in that: The p-type GaN current spreading layer has a flat surface on the side close to the p-type ohmic contact layer.

8. A method for preparing an island-shaped indium gallium nitrogen epitaxial structure, characterized in that: The following steps are involved: A nucleation layer, an n-type GaN current spreading layer, a stress presetting layer, an island generation layer, an island multi-quantum well barrier layer, a p-type electron blocking layer, a p-type GaN current spreading layer, and a p-type ohmic contact layer are sequentially grown on the surface of the growth substrate; The island generation layer is in an island growth mode during its growth process, and an island morphology is spontaneously formed on the surface; The island-shaped multi-quantum well barrier layer inherits the island-shaped morphology of the surface of the island-shaped generating layer and grows, and has micron-sized island-shaped structures distributed on the surface, and there are V-shaped grooves with openings upward between adjacent island-shaped structures; The island-shaped multi-quantum well barrier layer is a periodic structure of InGaN / GaN. On the original island-shaped morphology surface, the thickness of each InGaN quantum well layer in the longitudinal direction gradually increases from the lowest position of each island structure along the side wall to the highest position of the top, and the In component content gradually increases from the lowest position of each island structure along the side wall to the highest position of the top.

9. The method for preparing an island-shaped InGaN epitaxial structure according to claim 8, characterized in that: The growth temperature of the island generating layer is 550° C.-750° C., and the surface spontaneously forms an island morphology under the low temperature condition of 550° C.-750° C. and the compressive stress of the stress presetting layer.

10. A Micro LED chip, characterized in that: The Micro LED chip includes an island-shaped InGaN epitaxial structure as described in any one of claims 1 to 7.

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