A micro light-emitting diode epitaxial structure and a preparation method thereof

Abstract

The present invention provides a micro-LED epitaxial structure, which at least includes an N-type layer, a light-emitting layer, and a P-type layer. The light-emitting layer includes quantum well structures with n periods, and each period of the quantum well structure includes a well layer and a barrier layer. Among them, the quantum well structures with n1 periods are defined as the first light-emitting region, and the quantum well structures with n2 periods are defined as the second light-emitting region. n1 and n2 are greater than or equal to 1, and n1 + n2 is less than or equal to n. The first light-emitting region is closer to the N-type layer than the second light-emitting region. The average band gaps of the barrier layer materials of the two light-emitting regions satisfy the following conditions: the first light-emitting region is less than the second light-emitting region; the average band gaps of the well layer materials of the two light-emitting regions satisfy the following conditions: the first light-emitting region is greater than or equal to the second light-emitting region. The micro-LED prepared by using this epitaxial structure can achieve a peak photoelectric conversion efficiency corresponding to a current density lower than 1 A / cm<supgt;2< / supgt>, and the photoelectric conversion efficiency is increased by about 30%.

Description

Technical Field

[0001] The present invention relates to a micro-LED light-emitting element, belonging to the field of semiconductor optoelectronic technology. Background Art

[0002] The peak optoelectronic conversion efficiency of traditional epitaxial structure LEDs is distributed in the current density range greater than 5 A / cm 2 , such as Figure 9 shown, most of the existing applications work in the high current density (greater than 10 A / cm 2 ). However, the current used by Micro LEDs for mobile phones (or watches, bracelets) is very small, often at the nA level. Converted to current density, it is between 0.1 and 1 A / cm 2 . The optoelectronic conversion efficiency of the traditional epitaxial structure is in a very unstable range at current densities below 1 A / cm 2 . With a slight change in current, the optoelectronic conversion efficiency will also drop rapidly, resulting in the inability of traditional epitaxial wafers to be applied to products with low current density working requirements.

[0003] Therefore, for Micro LED chips for mobile phones (or watches, bracelets), it is necessary to develop an LED epitaxial wafer with a peak optoelectronic conversion efficiency in the low current density range and a stable optoelectronic conversion efficiency. A method for growing a Micro LED multi-quantum well layer proposed in Patent CN107833953A. The MQW structure is a well layer (InGaN) / barrier layer (GaN) / barrier layer (GaN with H2). By introducing H2 into the barrier layer and inserting a barrier layer between the well and barrier layers, the improvement of the lattice quality and well-barrier stress of the MQW is limited. It is necessary to propose a technical solution to further improve the low current characteristics of micro light-emitting diodes. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention aims to provide a micro-LED epitaxial structure and a preparation method thereof.

[0005] As an aspect of the present invention, the present invention proposes a micro-LED epitaxial structure, which at least includes an N-type layer, a light-emitting layer, and a P-type layer. The light-emitting layer includes n periods of quantum well structures, and each period of quantum well structure includes a well layer and a barrier layer. Among them, n1 periods of quantum well structures are defined as the first light-emitting region, and n2 periods of quantum well structures are defined as the second light-emitting region. n1 and n2 are greater than or equal to 1, and n1 + n2 is less than or equal to n. The first light-emitting region is closer to the N-type layer than the second light-emitting region. The average band gaps of the barrier layer materials of the two light-emitting regions satisfy the following conditions: the first light-emitting region is less than the second light-emitting region; the average band gaps of the well layer materials of the two light-emitting regions satisfy the following conditions: the first light-emitting region is greater than or equal to the second light-emitting region.

[0006] Preferably, the quantum well structure of each period in the first light-emitting region includes at least a first barrier layer, a second barrier layer, a third barrier layer, and a well layer, where the second barrier layer is located between the first barrier layer and the third barrier layer. In the first light-emitting region, the bandgap of the material of the second barrier layer in each quantum well structure is greater than the bandgaps of the materials of the first barrier layer and the third barrier layer.

[0007] Preferably, the quantum well structure of each period in the second light-emitting region includes at least a first barrier layer, a second barrier layer, a third barrier layer, a well layer, and a fourth barrier layer, where the second barrier layer is located between the first barrier layer and the third barrier layer, and the fourth barrier layer is located after the well layer. In the second light-emitting region, the bandgap of the material of the second barrier layer in each quantum well structure is greater than the bandgaps of the materials of the first barrier layer and the third barrier layer, and the bandgap of the fourth barrier layer is greater than the bandgaps of the materials of the first barrier layer, the second barrier layer, and the third barrier layer.

[0008] Preferably, the thickness ranges of the first barrier layer, the second barrier layer, the third barrier layer, and the fourth barrier layer are 10 Å to 1000 Å; the thickness range of the well layer is 1 Å to 100 Å. More preferably, in the quantum well structure of each period, the ratio of the total thickness of the first barrier layer, the second barrier layer, and the third barrier layer to the thickness of the well layer is between 5:1 and 20:1; the ratio of the thickness of the fourth barrier layer to the thickness of the well layer is between 5:1 and 20:1.

[0009] Preferably, in each period of the quantum well structure, the thickness of the second barrier layer is greater than the thicknesses of the first barrier layer and the third barrier layer.

[0010] Preferably, in the quantum well structure of the second light-emitting region, the thickness of the fourth barrier layer is greater than the thicknesses of the first barrier layer and the third barrier layer.

[0011] Preferably, in the two groups of light-emitting regions, the first barrier layer, the second barrier layer, and the third barrier layer are all or partially n-type doped, and the fourth barrier layer is an unintentionally doped layer. More preferably, the concentration of the n-type doping is 1E17 / cm 2 ~1E19 / cm 2 。

[0012] Preferably, the number of periods of the first light-emitting region is 1 to 5, and the number of periods of the second light-emitting region is 1 to 5. The material components of the quantum well structure in each period of the first and second light-emitting regions are the same.

[0013] Preferably, the well layer is composed of Al x In y Ga 1-x-y N material; the first barrier layer, the second barrier layer, the third barrier layer, and the fourth barrier layer are composed of AL p In q Ga1-p-q Composed of N materials, in the quantum well structure of each period, 0 ≤ x < p < 1; 0 ≤ q < y < 1.

[0014] Preferably, the average Al component percentage content of the barrier layer materials in the two light-emitting regions satisfies the following conditions: the first light-emitting region is less than the second light-emitting region; the average In component percentage content of the well layer materials in the two light-emitting regions satisfies the following conditions: the first light-emitting region is less than or equal to the second light-emitting region. Within each quantum well structure, the average Al component percentage content of the second barrier layer material is greater than that of the first barrier layer and the third barrier layer materials. Within the quantum well structure of the second light-emitting region, the average Al component percentage content of the fourth barrier layer material is greater than that of the first barrier layer, the second barrier layer, and the third barrier layer materials.

[0015] As another embodiment of the present invention, the light-emitting region further includes a third light-emitting region, the third light-emitting region includes n3 periods of quantum well structures, the third light-emitting region is located between the first light-emitting region and the second light-emitting region, and the bandgap of the barrier layer of the third light-emitting region is between that of the first light-emitting region and the second light-emitting region; the bandgap of the well layer of the third light-emitting region is between that of the first light-emitting region and the second light-emitting region.

[0016] Preferably, the average Al component percentage content of the barrier layer of the third light-emitting region is between that of the first light-emitting region and the second light-emitting region; the average In component percentage content of the well layer of the third light-emitting region is between that of the first light-emitting region and the second light-emitting region.

[0017] Preferably, the third light-emitting region includes a first barrier layer, a second barrier layer, a third barrier layer, and a well layer; the bandgap of the second barrier layer material in the third light-emitting region is greater than that of the first barrier layer and the third barrier layer materials.

[0018] Preferably, the thickness of the second barrier layer in the third light-emitting region is greater than that of the first barrier layer and the third barrier layer.

[0019] Preferably, the thickness ranges of the first barrier layer, the second barrier layer, and the third barrier layer in the third light-emitting region are 10 Å to 1000 Å; the thickness range of the well layer is 1 Å to 100 Å. The ratio of the total thickness of the first barrier layer, the second barrier layer, and the third barrier layer to the thickness of the well layer in the third light-emitting region is between 5:1 and 20:1.

[0020] Preferably, the first barrier layer, the second barrier layer, and the third barrier layer in the third light-emitting region are all or partially n-type doped. More preferably, the concentration of the n-type doping is 1E17 / cm 2 ~1E19 / cm 2 .

[0021] Preferably, the number of periods of the third light-emitting region is 0 to 5. The material components of the quantum well structure within each period of the third light-emitting region are the same.

[0022] Preferably, the well layer of the third light-emitting region is composed of Al x In y Ga 1-x-y N material; the first barrier layer, the second barrier layer, and the third barrier layer are composed of AL p In q Ga 1-p-q N material, where 0 ≤ x < p < 1; 0 ≤ q < y < 1.

[0023] Preferably, within each quantum well structure of the third light-emitting region, the average Al component percentage content of the second barrier layer material is greater than that of the first barrier layer and the third barrier layer materials.

[0024] As a second aspect of the present invention, the present invention provides a method for preparing the foregoing micro-LED epitaxial structure, and the preparation method includes the following process steps:

[0025] (1) Provide a substrate;

[0026] (2) Grow a nucleation layer, an N-type layer, and a light-emitting layer on the substrate;

[0027] (3) Grow a P-type layer.

[0028] Preferably, the average growth rate of the barrier layer of the first light-emitting region is greater than that of the barrier layer of the second light-emitting region; the average growth rate of the well layer of the first light-emitting region is greater than that of the well layer of the second light-emitting region.

[0029] Preferably, within each quantum well structure, the average growth rate of the first barrier layer and the third barrier layer is less than or equal to that of the second barrier layer.

[0030] Preferably, the growth rate range of the barrier layer is 0.1 to 10 Å / s; the growth rate range of the well layer is 0 to 1 Å / s.

[0031] Preferably, the growth temperature of the barrier layer is 700 to 950 °C; the growth temperature of the well layer is 700 to 900 °C.

[0032] Preferably, the growth mode of the barrier layer and the well layer in the composite light-emitting region is continuous growth or interrupted growth.

[0033] As a third aspect of the present invention, the present invention provides a micro light-emitting diode, and the micro light-emitting diode includes the foregoing epitaxial structure.

[0034] Preferably, the horizontal size of the micro light-emitting diode is between 1μm * 1μm and 300μm * 300μm.

[0035] The present invention also provides a light-emitting device, which includes the aforementioned micro light-emitting diode.

[0036] The micro-LED epitaxial structure and the micro light-emitting diode proposed by the present invention have the following beneficial effects:

[0037] (1) The light-emitting layer is designed as a composite light-emitting region structure, which effectively suppresses the carrier overflow in the light-emitting region, increases the electron-hole wave function overlap, and at the same time ensures that the stress of the light-emitting region material is effectively released, thereby improving the carrier transport and recombination behavior under small current injection, and improving the carrier radiative recombination efficiency and the photoelectric conversion efficiency;

[0038] (2) By growing a thinner well layer, a thicker barrier layer, and a larger barrier-well layer thickness ratio for each light-emitting region, the defect density of MQW growth can be reduced, the growth quality of MQW can be significantly improved, the non-radiative recombination centers can be reduced, so that the current density corresponding to the peak photoelectric conversion efficiency is significantly reduced, and the peak photoelectric conversion efficiency is significantly improved;

[0039] (3) By setting different growth rates for different light-emitting regions, the lattice mismatch stress between the barrier layer and the well layer in the MQW region can be further improved, and the MQW crystal quality can be improved. Since the main light-emitting layer of the LED is mainly the light-emitting layer close to the P-type side, by growing the MQW (the first light-emitting region) close to the N-type side at a relatively high speed and growing the MQW (the second light-emitting region) close to the P-type layer side at a low speed, the lattice mismatch stress between the high-In region of the light-emitting layer and the underlying GaN can be further reduced, the lattice quality of the main light-emitting region of MQW can be effectively improved, and at the same time, the growth time can be kept short, and the production efficiency can be improved;

[0040] (4) Within each quantum well period, by adjusting the growth rates of the barrier layer and the well layer in different growth temperature ranges, the lattice mismatch stress between the barrier layer and the well layer within a single light-emitting region growth period can be further improved, and the MQW crystal quality can be improved. Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0042] Figure 1 It is a schematic diagram of the epitaxial structure of Embodiment 1.

[0043] Figure 2 It is a schematic structural diagram of the first light-emitting region in the first embodiment.

[0044] Figure 3 It is a schematic structural diagram of the third light-emitting region in the first embodiment.

[0045] Figure 4 It is a schematic structural diagram of the second light-emitting region in the first embodiment.

[0046] Figure 5 It is a schematic energy band structure diagram of the composite light-emitting region in the first embodiment.

[0047] Figure 6 It is a schematic structural diagram of the first light-emitting region in the second embodiment.

[0048] Figure 7 It is a schematic structural diagram of the third light-emitting region in the second embodiment.

[0049] Figure 8 It is a schematic structural diagram of the second light-emitting region in the second embodiment.

[0050] Figure 9 It is a trend graph of WPE (photovoltaic conversion efficiency)-J (current density) of a traditional epitaxial structure LED.

[0051] Figure 10 It is a comparison of luminance (LOP)-wavelength (WLD) of the micro-LED of the epitaxial structure in the first embodiment with that of the traditional structure under a current density of 0.5 A / cm 2

[0052] Figure 11 It is a comparison of the test data of WPE (photovoltaic conversion efficiency)-J (current density) of the micro-LED of the epitaxial structure in the first embodiment with that of the traditional structure.

[0053] Description of component numbers in the supplementary figure: Substrate 1, U-GaN layer 2, N-GaN layer 3, stress release layer 4, first light-emitting region 5 (including first barrier layer 5A, second barrier layer 5B, third barrier layer 5C, well layer 5D), third light-emitting region 6 (including first barrier layer 6A, second barrier layer 6B, third barrier layer 6C, well layer 6D), second light-emitting region 7 (including first barrier layer 7A, second barrier layer 7B, third barrier layer 7C, well layer 7D, fourth barrier layer 7G), PGaN layer 8, first well layer 52D / 62D / 72D, second well layer 52E / 62E / 72E, third well layer 52F / 62F / 72F. Detailed implementation manners

[0054] ​The embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings and examples, so as to fully understand how the present invention uses technical means to solve technical problems and achieve the implementation process of technical effects and implement accordingly. It should be noted that as long as there is no conflict, the various embodiments in the present invention and the various features in each embodiment can be combined with each other, and the formed technical solutions are all within the protection scope of the present invention.

[0055] Embodiment 1

[0056] Please refer to Figures 1 to 5 , for the purpose of the present invention, this embodiment provides a micro-LED epitaxial structure and a manufacturing method thereof, including the following process steps:

[0057] (1) Provide a substrate 1, which can be selected from at least one of sapphire (Al 2 O 3 ), AlN-coated or SiNx-coated sapphire (Al 2 O 3 ), Ga 2 O 3 ), AlN-coated or SiNx-coated Ga 2 O 3 ), SiC, GaN, ZnO, Si or Ge. In this embodiment, an AlN-coated sapphire substrate is preferably used.

[0058] (2) Epitaxially grow a nucleation layer (not shown in the figure) on the substrate 1: Preferably, an AlGaN material is used, and the epitaxial growth method can be selected from MOCVD (metal organic chemical vapor deposition) method, MBE (molecular beam epitaxy) method, CVD (chemical vapor deposition) method, HVPE (hydride vapor phase epitaxy) method, PECVD (plasma enhanced chemical vapor deposition) method. MOCVD is preferably used, but the embodiment is not limited thereto. Put the AlN-coated sapphire substrate into a metal organic chemical vapor deposition (MOCVD) chamber, first perform hydrogenation treatment to remove impurities on the substrate surface, and then reduce the temperature to about 500-600 °C to grow a nucleation layer with a thickness of about 20 nm.

[0059] (3) Epitaxially grow a U-GaN layer 2 and an N-GaN layer 3 on the nucleation layer in sequence. The U-GaN layer 2 is used to reduce the lattice mismatch caused by the lattice constant difference between the substrate and the N-GaN layer and enhance the crystallization performance of the semiconductor layer formed on this layer. This embodiment is not limited thereto. The growth mode of the U-GaN layer 2 is a three-dimensional mode + two-dimensional mode. On the basis of the nucleation layer, island growth is first formed to maximize the turning and merging of dislocations, and then it turns to the two-dimensional mode to form a flat surface, with a growth thickness of about 1-3 um. Then grow the N-GaN layer 3, the thickness of the N-GaN layer 3 is 1-3 um, and the doping level is 1E19-2.5E19 / cm 2between

[0060] (4) Stress release layer 4, cool down to 750 - 950 °C, grow the stress release layer, the material is preferably InGaN and GaN, which is an alternating superlattice structure or a combined form of the materials therein. The purpose is to further reduce the lattice mismatch dislocation between the high In-component material of the subsequent light-emitting layer and the underlying GaN material, release stress, and improve the crystal quality.

[0061] (5) First light-emitting region 5, change the temperature to the barrier layer temperature, at 800 - 900 °C, grow the first barrier layer 5A. In this embodiment, the first barrier layer is preferably a Si-doped GaN material, with a thickness of about 5 - 50 Å, a growth rate of about 0.9 Å / s, and a Si doping level of about 1E17 / cm 2 ~ 1E19 / cm 2 . After the growth of the first barrier layer 5A is completed, raise the temperature by 10 - 50 °C to grow the second barrier layer 5B. The second barrier layer is a Si-doped AlGaN material, with a thickness of about 30 - 100 Å, a growth rate of about 1.5 Å / s, introduce TMAL at 2 sccm, and the Al component is about 1 - 10%. In this embodiment, 1.5% is preferably selected, and the Si doping level is about 1E17 / cm 2 ~ 1E19 / cm 2 . After the growth of the second barrier layer 5B is completed, stop introducing TMAL, cool down by 10 - 50 °C to grow the third barrier layer 5C. The third barrier layer 5C is a Si-doped GaN material, with a thickness of about 5 - 50 Å, a growth rate of about 0.9 Å / s, and a Si doping level of about 1E17 / cm 2 ~ 1E19 / cm 2 . After the growth of the third barrier layer 5C is completed, stop introducing SiH4, cool down to 700 - 800 °C, grow the well layer 5D, the material is InGaN, introduce TMIN at 800 sccm, with a thickness of about 5 - 50 Å, a growth rate of about 0.3 Å / s. In this embodiment, 20 Å is preferably selected, and the average In component of the well layer is about 18%. The number of periods of the first light-emitting region is 1 - 5, and the material components of the quantum well structure within each period are the same. In this embodiment, the number of alternating stacks in the first light-emitting region is preferably 2 times. Among them, the bandgap of the second barrier layer material is greater than or equal to the bandgaps of the first barrier layer and the third barrier layer materials, aiming to effectively suppress carrier overflow and adjust the energy band structure of the light-emitting region. The temperature change and growth rate change of the first barrier layer, the first barrier layer, and the third barrier layer are for the purpose of improving the crystal quality of the MQW region material by adjusting the growth rate of the barrier layer in different growth temperature ranges while improving production efficiency.

[0062] (6) The third light-emitting region 6 is heated to 800 - 900 °C to grow the third light-emitting region 6. First, the first barrier layer 6A is grown. In this embodiment, GaN material is preferably used, which is an unintentionally doped layer with a growth rate of about 0.6 Å / s and a thickness of about 5 - 50 Å. After the growth of the first barrier layer 6A is completed, the temperature is increased by 10 - 50 °C to grow the second barrier layer 6B. The material of the second barrier layer is Si-doped AlGaN material with a growth rate of about 0.9 Å / s and a thickness of about 30 - 100 Å. TMAL is introduced at 2.5 sccm, and the Al component is about 1 - 10%, preferably 2% in this embodiment. The Si doping level is about 1E17 / cm 2 ~1E19 / cm 2 After the growth of the second barrier layer 6B is completed, the introduction of TMAL is stopped, and the temperature is decreased and then increased by 10 - 50 °C to grow the third barrier layer 6C. The third barrier layer 6C is Si-doped GaN material with a growth rate of about 0.6 Å / s and a thickness of about 5 - 50 Å. The Si doping level is about 1E17 / cm 2 ~1E19 / cm 2 After the growth of the third barrier layer 6C is completed, the introduction of SiH4 is stopped, and the temperature is decreased to 700 - 800 °C to grow the well layer 6D. The material is InGaN. TMIN is introduced at 900 sccm, and the growth rate is about 0.2 Å / s and the thickness is about 5 - 50 Å, preferably 20 Å in this embodiment. The average In component of the well layer is about 19%. The number of periods of the third light-emitting region is 0 - 5, and the material components of the quantum well structures within each period are the same. In this embodiment, the preferred number of alternating stacking times of the third light-emitting region is 2. Among them, the average bandgap of the barrier layer of the third light-emitting region is greater than that of the first light-emitting region, and the average bandgap of the well layer of the third light-emitting region is less than that of the first light-emitting region. The purpose is to effectively ensure that the carrier overflow of the light-emitting region near the P-type side is effectively suppressed, and at the same time ensure that the stress of the light-emitting region material is effectively released, thereby improving the carrier transport and recombination behavior under low-current injection; the growth rate of the barrier layer of the third light-emitting region is less than or equal to that of the barrier layer of the first light-emitting region, and the growth rate of the well layer of the third light-emitting region is less than or equal to that of the well layer of the first light-emitting region. The purpose is to obtain better crystal quality through the lower growth rate of the light-emitting region near the P-type side.

[0063] After the growth of the third light-emitting region is completed, the temperature is raised to 800 - 900 °C to grow the second light-emitting region 7. First, the first barrier layer 7A is grown. In this embodiment, GaN material is preferably used, which is an unintentionally doped layer with a growth rate of about 0.3 Å / s and a thickness of about 5 - 50 Å. After the growth of the first barrier layer 7A is completed, the temperature is raised by 10 - 50 °C to grow the second barrier layer 7B. The material of the second barrier layer is Si-doped AlGaN material with a growth rate of about 0.5 Å / s and a thickness of about 30 - 100 Å. TMAL is introduced at 3 sccm, and the Al component is about 1 - 10%, preferably 2.5% in this embodiment. The Si doping level is about 1E17 / cm 2 ~1E19 / cm 2 . After the growth of the second barrier layer 7B is completed, the introduction of TMAL is stopped, and the temperature is lowered by 10 - 50 °C to grow the third barrier layer 7C. The third barrier layer 7C is Si-doped GaN material with a growth rate of about 0.3 Å / s and a thickness of about 5 - 50 Å. After the growth of the third barrier layer 7C is completed, the temperature is lowered to 700 - 800 °C to grow the well layer 7D. The material is InGaN, TMIN is introduced at 1000 sccm, the growth rate is about 0.1 Å / s, and the thickness is about 5 - 50 Å, preferably 20 Å in this embodiment. The average In component of the well layer is about 20%. After the growth of the well layer is completed, the temperature is raised to 800 - 900 °C to grow the fourth barrier layer 7G. The material of the fourth barrier layer is GaN / AlGaN with a rate of 0.5 Å / s and a thickness of about 50 - 100 Å. The average Al component of the fourth barrier layer is about 5 - 50%, preferably 15% in this embodiment. The number of periods of the second light-emitting region is 1 - 5, and the material components of the quantum well structures within each period are the same. In this embodiment, the number of alternating stacks of the second light-emitting region is preferably 1 time. As Figure 5 shown, the average bandgap of the barrier layers in the second light-emitting region is greater than the average bandgaps of the third and first light-emitting regions, and the average bandgap of the well layer in the second light-emitting region is less than the average bandgaps of the third and first light-emitting regions; the bandgap of the fourth barrier layer material is greater than or equal to the bandgaps of the first, second, and third barrier layer materials. The highest bandgap of the fourth barrier layer material is designed to effectively block electron overflow and improve the carrier transport and recombination behavior under low current injection. The growth rate of the well layer in the second light-emitting region is less than or equal to the growth rates of the well layers in the third and first light-emitting regions. The purpose is to obtain better crystal quality through the light-emitting region closer to the P-type side with a lower growth rate, thereby improving the carrier recombination behavior under low current injection and further enhancing the light-emitting efficiency under low current injection.

[0064] In summary, through the design of the composite structure of the MQW light-emitting region, the carrier injection efficiency and recombination efficiency are improved, carrier overflow can be effectively suppressed, and the overlap of electron-hole wave functions is increased, thereby improving the carrier transport and recombination behaviors under low-current injection; by controlling the thickness and growth rate of different regions of the MQW growth, the lattice mismatch between the MQW and the underlying layer and between the wells and barriers in the MQW is reduced, the stress is reduced, and the growth quality of the MQW is improved, enabling the peak efficiency to shift towards a low current density and enhancing the light-emitting efficiency at low currents.

[0065] (8)After the growth of the light-emitting layer is completed, a low-temperature p-type layer is grown. On the one hand, it is to protect the MQW from being damaged by subsequent high temperatures, and on the other hand, it provides a high hole injection.

[0066] (9)After that, the temperature is raised to grow the high-temperature PAlGaN and high-temperature PGaN layers to flatten the surface.

[0067] (10)The epitaxial wafer with this epitaxial structure is fabricated into an LED chip. The horizontal size of the chip is 19μm * 31μm. When tested in the chip state, as Figure 10 shown, the data shows that at a current density of 0.5 A / cm 2 , the brightness is increased by about 30% compared with the traditional structure. After packaging, the test of the change of the photoelectric conversion efficiency (WPE) with the current density (J) is carried out. As Figure 11 shown, the data shows that the current density (J) corresponding to the peak photoelectric conversion efficiency (peak-WPE) decreases from 4.0 A / cm 2 to 0.7 A / cm 2 .

[0068] Embodiment 2

[0069] In this embodiment, an alternative implementation scheme is provided, specifically as follows.

[0070] The description of the light-emitting region is as follows: The difference from Embodiment 1 is as follows. This embodiment is a multi-well layer design, as follows:

[0071] The first light-emitting region: Refer to Figure 6 . After the growth of the third barrier layer 5C is completed, during the process of cooling to the well layer temperature (700 - 800 °C), the growth of the first well layer 52D is started. TMIN is introduced at 1000 sccm, the material is InGaN, the rate is about 0.6 Å / s, and the thickness is about 3 - 8 Å. After the growth of the first well layer is completed, the growth of the second well layer 52E is started. The material is InGaN, the rate is about 0.3 Å / s, and the thickness is about 5 - 15 Å. After the growth of the second well layer is completed, during the process of heating to the barrier layer temperature (800 - 900 °C), the growth of the third well layer 52F is started. The material is InGaN, the rate is about 0.6 Å / s, and the thickness is about 3 - 8 Å. The average In composition is about 20%.

[0072] The third light-emitting region: Refer to Figure 7 . After the growth of the third barrier layer 6C is completed, when cooling down to the well layer temperature (700 - 800 °C), the growth of the first well layer 62D starts immediately. The material is InGaN, with TMIN introduced at 1000 sccm, a rate of approximately 0.4 Å / s, and a thickness of approximately 3 - 8 Å. After the growth of the first well layer is completed, the growth of the second well layer 62E starts. The material is InGaN, with a rate of approximately 0.2 Å / s and a thickness of approximately 5 - 15 Å. After the growth of the second well layer is completed, when heating up to the barrier layer temperature (800 - 900 °C), the growth of the third well layer 62F starts immediately. The material is InGaN, with a rate of approximately 0.4 Å / s and a thickness of approximately 3 - 8 Å. The average In composition is approximately 20%.

[0073] The second light-emitting region: Refer to Figure 8 . After the growth of the third barrier layer 7C is completed, during the process of cooling down to the well layer temperature (700 - 800 °C), the growth of the first well layer 72D starts immediately. The material is InGaN, with TMIN introduced at 1000 sccm, a rate of approximately 0.2 Å / s, and a thickness of approximately 3 - 8 Å. After the growth of the first well layer 72D is completed, the growth of the second well layer 72E starts. The material is InGaN, with a rate of approximately 0.1 Å / s and a thickness of approximately 5 - 15 Å. After the growth of the second well layer 72E is completed, when heating up to the barrier layer temperature (800 - 900 °C), the growth of the third well layer 72F starts immediately. The material is InGaN, with a rate of approximately 0.1 Å / s and a thickness of approximately 3 - 8 Å. The average In composition is approximately 20%.

[0074] This embodiment is a multi-well layer design, aiming to further reduce the lattice mismatch stress between the high In composition well layer and the barrier layer. This design can further improve the mismatch stress of the barrier and well layers within a single growth cycle and the MQW crystal quality by adjusting the growth rates of the well layers in different growth temperature ranges, thereby improving the low-current characteristics of the device.

[0075] Embodiment Three

[0076] In this embodiment, an alternative implementation is provided, specifically as follows. The difference from Embodiment One is that the composite light-emitting region is a combined form of the first light-emitting region and the second light-emitting region.

[0077] Embodiment Four

[0078] In this embodiment, alternative implementation schemes are provided, specifically as follows. Epitaxial structure: substrate, nucleation layer, UGaN, NGaN layer, stress release layer, P-type layer. The description of the light-emitting region is as follows: The difference from the first embodiment is that the material of the fourth barrier layer in the second light-emitting region is a combination of GaN / AlGaN / AlN or an overlapping combination structure thereof, such as (GaN / AlGaN / AlN) overlapping N times, (GaN / AlGaN) overlapping N times / AlN, GaN / (AlGaN / AlN) overlapping N times, where 1 ≤ N ≤ 20. The average Al component range is 5% - 50%. The fourth barrier layer in this embodiment is designed as a combination of GaN / AlGaN / AlN or an overlapping combination structure thereof, aiming to further reduce electron overflow, increase the overlap of electron-hole wave functions, improve the carrier recombination behavior under low current injection, and enhance the brightness at low current density.

[0079] The above embodiments merely illustrate the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A micro-LED epitaxial structure: The epitaxial structure at least includes an N-type layer, a light-emitting layer, and a P-type layer. The light-emitting layer includes n periods of quantum well structures. Each period of the quantum well structure includes a well layer and a barrier layer. Among them, n1 periods of quantum well structures are defined as the first light-emitting region, and n2 periods of quantum well structures are defined as the second light-emitting region. n1 and n2 are greater than or equal to 1, and n1 + n2 is less than or equal to n. The first light-emitting region is closer to the N-type layer than the second light-emitting region; Each period of the quantum well structure in the second light-emitting region at least includes a first barrier layer, a second barrier layer, a third barrier layer, a well layer, and a fourth barrier layer. The second barrier layer is located between the first barrier layer and the third barrier layer, and the fourth barrier layer is located after the well layer. In the second light-emitting region, the average Al component percentage content of the second barrier layer material in each quantum well structure is greater than that of the first barrier layer and the third barrier layer materials, and the average Al component percentage content of the fourth barrier layer is greater than that of the first barrier layer, the second barrier layer, and the third barrier layer materials.

2. A micro-LED epitaxial structure according to claim 1, wherein: Each period of the quantum well structure in the first light-emitting region at least includes a first barrier layer, a second barrier layer, a third barrier layer, and a well layer. The second barrier layer is located between the first barrier layer and the third barrier layer. In the first light-emitting region, the average Al component content of the second barrier layer material in each quantum well structure is greater than that of the first barrier layer and the third barrier layer materials.

3. A micro-LED epitaxial structure according to claim 2, wherein: The thickness ranges of the first barrier layer, the second barrier layer, the third barrier layer, and the fourth barrier layer are 10 Å to 1000 Å; The thickness range of the well layer is 1 Å to 100 Å.

4. A micro-LED epitaxial structure according to claim 2, wherein: In each period of the quantum well structure, the ratio of the total thickness of the first barrier layer, the second barrier layer, and the third barrier layer to the thickness of the well layer is between 5:1 and 20:

1.

5. A micro-LED epitaxial structure according to claim 1, wherein: The ratio of the thickness of the fourth barrier layer to the thickness of the well layer is between 5:1 and 20:

1.

6. A micro-LED epitaxial structure according to claim 2, wherein: In each period of the quantum well structure, the thickness of the second barrier layer is greater than that of the first barrier layer and the third barrier layer.

7. A micro-LED epitaxial structure according to claim 1, wherein: In each period of the quantum well structure in the second light-emitting region, the thickness of the fourth barrier layer is greater than that of the first barrier layer and the third barrier layer.

8. A micro-LED epitaxial structure according to claim 2, wherein: In the two groups of light-emitting regions, the first barrier layer, the second barrier layer, and the third barrier layer are all or partially n-type doped, and the fourth barrier layer is an unintentionally doped layer.

9. A micro-LED epitaxial structure according to claim 8, wherein: In the two sets of light-emitting regions described above, the first barrier layer, the second barrier layer, and the third barrier layer are all or partially n-type doped, and the concentration of n-type doping is 1E17 / cm 2 ~1E19 / cm 2 .

10. A micro-LED epitaxial structure according to claim 1, characterized in that: the number of periods of the first light-emitting region is 1 to 5, and the number of periods of the second light-emitting region is 1 to 5.

11. A micro-LED epitaxial structure according to claim 2, characterized in that: The well layer is composed of Al x In y Ga 1-x-y N materials; the first barrier layer, the second barrier layer, the third barrier layer, and the fourth barrier layer are composed of AL p In q Ga 1-p-q N materials, in the quantum well structure of each period, 0 ≤ x < p < 1; 0 ≤ q < y < 1.

12. A micro-LED epitaxial structure according to claim 1, characterized in that: the average Al component percentage content of the barrier layer materials of the two groups of light-emitting regions satisfies the following conditions: the first light-emitting region is less than the second light-emitting region; the average In component percentage content of the well layer materials of the two groups of light-emitting regions satisfies the following conditions: the first light-emitting region is less than or equal to the second light-emitting region.

13. A micro-LED epitaxial structure according to claim 1, characterized in that: the light-emitting region further includes a third light-emitting region, the third light-emitting region includes a quantum well structure with n3 periods, the third light-emitting region is located between the first light-emitting region and the second light-emitting region, and the content of the Al component of the barrier layer of the third light-emitting region is between that of the first light-emitting region and the second light-emitting region; the content of the In component of the well layer of the third light-emitting region is between that of the first light-emitting region and the second light-emitting region.

14. A micro-LED epitaxial structure according to claim 13, characterized in that: the third light-emitting region includes a first barrier layer, a second barrier layer, a third barrier layer, and a well layer; the average Al component percentage content of the material of the second barrier layer in the third light-emitting region is greater than the average Al component percentage content of the materials of the first barrier layer and the third barrier layer.

15. A micro-LED epitaxial structure according to claim 14, characterized in that: the thickness of the second barrier layer in the third light-emitting region is greater than the thicknesses of the first barrier layer and the third barrier layer.

16. A micro-LED epitaxial structure according to claim 14, characterized in that: the thickness ranges of the first barrier layer, the second barrier layer, and the third barrier layer in the third light-emitting region are 10 Å to 1000 Å; the thickness range of the well layer is 1 Å to 100 Å.

17. A micro-LED epitaxial structure according to claim 14, characterized in that: the ratio of the total thickness of the first barrier layer, the second barrier layer, and the third barrier layer to the thickness of the well layer in the third light-emitting region is between 5:1 and 20:

1.

18. A micro-LED epitaxial structure according to claim 14, characterized in that: The first barrier layer, the second barrier layer, and the third barrier layer in the third light-emitting region are all or partially n-type doped, and the concentration of the n-type doping is 1E17 / cm 2 ~1E19 / cm 2 .

19. A micro-LED epitaxial structure according to claim 13, characterized in that: the number of periods of the third light-emitting region is 0 to 5.

20. A micro-light-emitting diode, characterized in that, it includes the epitaxial structure described in any one of the foregoing claims 1 to 19.

21. A micro-light-emitting diode according to claim 20, characterized in that: the horizontal size of the micro-light-emitting diode is between 1 μm * 1 μm and 300 μm * 300 μm.

22. A light-emitting device, characterized in that, it includes a micro-light-emitting diode described in claim 21.

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