Epitaxial structure for micro-LED, method for manufacturing, micro-LED and light-emitting device

Abstract

Epitaxial structure for micro-LED comprising at least one N-type layer, one light-emitting layer, and one P-type layer, wherein the light-emitting layer has a quantum well structure with n periods and the quantum well structure has a well layer and a barrier layer in each period, wherein the quantum well structure with n1 periods is defined as the first light-emitting region (5), and the quantum well structure with n2 periods is defined as the second light-emitting region (7), wherein n1 and n2 are greater than or equal to 1 and n1+n2 is less than or equal to n, wherein the first light-emitting region (5) is closer to the N-type layer than the second light-emitting region (7).wherein the average band gaps of the barrier layer materials of the two groups of light-emitting regions satisfy the following condition: the first light-emitting region is smaller than the second light-emitting region; and the average band gaps of the pot layer materials of the two groups of light-emitting regions satisfy the following condition: the first light-emitting region is greater than or equal to the second light-emitting region, wherein the quantum pot structure in each period in the second light-emitting region (7) comprises at least a first barrier layer (7A), a second barrier layer (7B), a third barrier layer (7C), a pot layer (7D), and a fourth barrier layer (7G), wherein the second barrier layer (7B) is located between the first barrier layer (7A) and the third barrier layer (7C), and the fourth barrier layer (7G) is located behind the pot layer (7D).wherein in the second light-emitting region (7) the band gap of the materials of the second barrier layer (7B) of each quantum well structure is larger than the band gap of the materials of the first barrier layer (7A) and the third barrier layer (7C), and the band gap of the materials of the fourth barrier layer (7G) is larger than the band gap of the materials of the first barrier layer, the second barrier layer and the third barrier layer.

Description

Background of the invention

[0001] The present invention relates to a light-emitting element for micro-LEDs and belongs to the field of optoelectronic semiconductor technology. State of the art

[0002] The peak photoelectric conversion efficiency of conventional epitaxial structures for LEDs corresponds to a current density range above 5A / cm². 3 , as in Fig. Figure 9 is shown, and most existing applications operate in the high current density range (over 10 A / cm²). 3 ). The micro-LEDs used in mobile phones (or watches and wristbands) often consume only very low currents in the nA range, corresponding to a current density of 0.1 to 1 A / cm². 3 This corresponds to the photoelectric conversion efficiency of conventional epitaxial structures at a current density of less than 1 A / cm². 3in a very unstable range, and with small changes in current the photoelectric conversion efficiency also drops rapidly, which means that epiwafers with conventional structures cannot be used in low current density products.

[0003] Therefore, there is a need to develop LED epiwafers for micro-LED chips used in mobile phones (or watches, wristbands) that exhibit peak photoelectric conversion efficiency at low current densities and stable photoelectric conversion efficiency. Document CN 1 07 833 953 A proposes a method for growing multi-quantum well (MQW) layers for micro-LEDs. The MQW structure consists of a well layer (InGaN) / blocking layer (GaN) / barrier layer (introducing H₂ into GaN), where H₂ is introduced into the barrier layer and a blocking layer is inserted between the well layer and the barrier layer. This approach only allows for limited improvements in the lattice quality and voltage of the well layer and barrier layer for MQW. It is therefore necessary to propose technical solutions that enable further improvement of the low-current properties of micro-LEDs.

[0004] DE 10 2014 117 611 A1 discloses an optoelectronic semiconductor chip. KR 10 2018 0 015 163 A discloses a light-emitting structure in which a charge carrier is selectively injected into several active layers. CN 1 03 682 001 A discloses a light-emitting diode based on group III nitride semiconductors. YANG, Y and ZENG, Y.: Efficiency Droop Reduction in InGaN LEDs by Alternating AlGaN Barriers With GaN Barriers. In: IEEE Photonics Technology Letters, Vol. 27, 2015, No. 8, pp. 844-847, discloses quantum barrier layers through alternating AlGaN barriers with GaN barriers in InGaN-based light-emitting diodes (LEDs). Subject matter of the invention

[0005] To solve the problems of the prior art, the present invention aims to provide an epitaxial structure for micro-LEDs and the method for manufacturing them.

[0006] As one aspect of the present invention, the present invention proposes an epitaxial structure for micro-LEDs comprising at least one N-type layer, a light-emitting layer, and a P-type layer, wherein the light-emitting layer has a quantum well structure with n periods, and the quantum well structure has a well layer and a barrier layer in each period, wherein the quantum well structure with n1 periods is defined as the first light-emitting region, and the quantum well structure with n2 periods is defined as the second light-emitting region, wherein n1 and n2 are greater than or equal to 1 and n1+n2 is less than or equal to n, and wherein the first light-emitting region is closer to the N-type layer than the second light-emitting region.wherein the average band gap of the barrier layer materials of the two groups of light-emitting regions satisfies the following condition: the first light-emitting region is smaller than the second light-emitting region; and the average band gap of the pot layer materials of the two groups of light-emitting regions satisfies the following condition: the first light-emitting region is greater than or equal to the second light-emitting region. Furthermore, the quantum pot structure in each period in the second light-emitting region comprises at least a first barrier layer, a second barrier layer, a third barrier layer, a pot layer, and a fourth barrier layer, wherein the second barrier layer is located between the first barrier layer and the third barrier layer, and the fourth barrier layer is located behind the pot layer.wherein in the second light-emitting region the band gap of the materials of the second barrier layer of each quantum well structure is larger than the band gap of the materials of the first barrier layer or the third barrier layer, and the band gap of the materials of the fourth barrier layer is larger than the band gap of the materials of the first barrier layer, the second barrier layer, or the third barrier layer.

[0007] Preferably, the quantum well structure in each period in the first light-emitting region comprises at least a first barrier layer, a second barrier layer, a third barrier layer and a well layer, wherein the second barrier layer of the quantum well structure in each period in the first light-emitting region is arranged between the first barrier layer of the quantum well structure in each period in the first light-emitting region and the third barrier layer of the quantum well structure in each period in the first light-emitting region, and in the first light-emitting region the band gap of the materials of the second barrier layer of each quantum well structure is larger than the band gap of the materials of the first barrier layer or the third barrier layer.

[0008] Preferably, the thicknesses of the first barrier layer, the second barrier layer, the third barrier layer, or the fourth barrier layer are in the range of 1 nm to 100 nm; and the thickness of the pot layer is in the range of 0.1 nm to 10 nm. Even more preferably, 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 pot layer in the quantum well structure is in a ratio of 5:1 to 20:1 in each period, and the thickness of the fourth barrier layer to the thickness of the pot layer is in a ratio of 5:1 to 20:1.

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

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

[0011] Preferably, the first, second, and third barrier layers in the two groups of light-emitting regions are fully or partially n-type doped, and the fourth barrier layer is unintentionally doped. Even more preferably, the concentration of the n-type doping is in the range of 1 × 10⁻¹⁷ / cm². 3 - 1E19 / cm 3 lies.

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

[0013] Preferably, the pot layer consists of the material Al x In y Ga 1-x-y N, and the first barrier layer, the second barrier layer, the third barrier layer and the fourth barrier layer consist of the material Al p In q Ga 1-p-q N, where the conditions 0≤x <p<1; 0≤q<y<1 in der Quantentopfstruktur in jeder Periode gelten.

[0014] Preferably, the average percentages of Al content in the barrier layer materials in the two groups of light-emitting regions satisfy the following condition: the first light-emitting region is smaller than the second light-emitting region; and the average percentages of In content in the pot layer materials in the two groups of light-emitting regions satisfy the following condition: the first light-emitting region is smaller than or equal to the second light-emitting region. In each quantum pot structure, the average percentage of Al content in the materials of the second barrier layer is greater than the average percentage of Al content in the materials of the first barrier layer or the third barrier layer.In the quantum well structure in the second light-emitting region, the average percentage of Al content in the materials of the fourth barrier layer is greater than the average percentage of Al content in the materials of the first barrier layer, the second barrier layer, or the third barrier layer.

[0015] In an alternative embodiment of the present invention, the light-emitting region further comprises a third light-emitting region, wherein the third light-emitting region has a quantum well structure with n3 periods and is arranged between the first light-emitting region and the second light-emitting region, wherein the band gap of the barrier layer in the third light-emitting region lies between that in the first light-emitting region and in the second light-emitting region; and the band gap of the well layer in the third light-emitting region lies between that in the first light-emitting region and in the second light-emitting region.

[0016] Preferably, the average percentage of Al content in the barrier layers in the third light-emitting area lies between that in the first light-emitting area and in the second light-emitting area; and the average percentage of In content in the pot layer in the third light-emitting area lies between that in the first light-emitting area and in the second light-emitting area.

[0017] Preferably, the third light-emitting region comprises a first barrier layer, a second barrier layer, a third barrier layer and a pot layer, wherein the band gap of the materials of the second barrier layer in the third light-emitting region is larger than the band gap of the materials of the first barrier layer or the third barrier layer.

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

[0019] Preferably, the thicknesses of the first barrier layer, the second barrier layer, and the third barrier layer in the third light-emitting region are in the range of 1 nm to 100 nm; and the thickness of the pot layer is in the range of 0.1 nm to 10 nm. The total thickness of the first barrier layer, the second barrier layer, and the third barrier layer to the thickness of the pot layer in the third light-emitting region is in a ratio of 5:1 to 20:1.

[0020] Preferably, the first barrier layer, the second barrier layer, and the third barrier layer in the third light-emitting region are fully or partially n-type doped. Even more preferably, the concentration of the n-type doping is in the range of 1 × 10⁻¹⁷ / cm². 3 - 1E19 / cm3 lies.

[0021] Preferably, the third light-emitting region has a period number of 0 to 5. The material compositions of the quantum well structure in each period of the third light-emitting region are the same.

[0022] Preferably the pot layer in the third light-emitting area consists of the material Al x In y Ga 1-x-y N; and the first barrier layer, the second barrier layer and the third barrier layer consist of the material Al p In q Ga 1-p-q N, where the conditions 0≤x <p<1; 0≤q<y<1 gelten.

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

[0024] As a second aspect of the present invention, the present invention proposes a method for producing the above-mentioned epitaxial structure for micro-LEDs, the method comprising the following steps: (1) A substrate is provided; (2) A nucleation layer, an N-type layer and a light-emitting layer grow on the substrate; (3) A P-type layer grows.

[0025] Preferably, the average growth rate of the barrier layer in the first light-emitting area is greater than the average growth rate of the barrier layer in the second light-emitting area. And the average growth rate of the potting layer in the first light-emitting area is greater than the average growth rate of the potting layer in the second light-emitting area.

[0026] Preferably, the average growth rate of the first barrier layer and the third barrier layer in each quantum well structure is less than or equal to the average growth rate of the second barrier layer.

[0027] Preferably, the growth rate of the barrier layer is in the range of 0.01 nm / s to 1 nm / s; and the growth rate of the pot layer is in the range of 0 nm / s to 0.1 nm / s.

[0028] Preferably, the growth temperature of the barrier layer is in the range of 700°C - 950°C; and the growth temperature of the pot layer is in the range of 700°C - 900°C.

[0029] Preferably, the growth of the barrier layer and the pot layer in the light-emitting composite area exhibits continuous or interrupted growth.

[0030] As a third aspect of the present invention, the present invention presents the micro-LED, wherein the micro-LED has the epitaxial structure mentioned above.

[0031] Preferably, the micro-LED has a horizontal dimension between 1 µm * 1 µm - 300 µm * 300 µm.

[0032] The invention further provides a light-emitting device, wherein the light-emitting device comprises the aforementioned micro-LED.

[0033] The epitaxial structure according to the invention for micro-LEDs and their micro-LEDs exhibit the following advantageous effects: (1) The light-emitting layer is designed with a structure of the light-emitting composite area, which effectively suppresses the overflow of charge carriers in the light-emitting area and increases the overlap of the electron-hole wave function, while at the same time ensuring effective relief of stresses in the materials in the light-emitting area, thus improving charge carrier transport and composite behavior at low current injection and increasing the efficiency of the combined charge carrier radiation and the photoelectric conversion efficiency. (2) By growing a thinner pot layer, thicker barrier layers and with a larger thickness ratio of the barrier layer to the pot layer in each light-emitting area, the defect density of the MQW growth is reduced, thereby significantly improving the growth quality of the MQW and reducing the non-radiating composite center, which ultimately leads to a significant reduction in the current density corresponding to the peak value of the photoelectric conversion efficiency and a significant increase in the peak value of the photoelectric conversion efficiency. (3) By adjusting different growth rates for different light-emitting regions, the lattice mismatch stress between the barrier layers and the pot layer in the MQW region is further improved to increase the MQW crystal quality.Since the most important light-emitting layer of the LED is mainly the light-emitting layer near the P-type side, the lattice mismatch voltage between the high In region and the lower GaN layer of the light-emitting layer can be further reduced, and the lattice quality of the most important light-emitting MQW region can be effectively improved while maintaining a short growth time, ultimately increasing production efficiency by allowing the MQW (in the first light-emitting region) near the N-type side to grow at a relatively higher rate and the MQW (in the second light-emitting region) near the P-type layer to grow at a lower rate. (4) In each period of the quantum well structure, the growth rates of the barrier layers and the pot layer are adjusted in different temperature ranges, thereby improving the stress for lattice mismatch in the barrier layers and the pot layer during the growth period of a single light-emitting region and thus increasing the MQW crystal quality. Attached drawings

[0034] To more clearly illustrate the technical solutions in the embodiments or prior art of the present invention, a brief description of the accompanying drawings follows, which must be used when describing the embodiments or prior art. It is obvious that the accompanying drawings in the following description relate only to the embodiments of the present invention. Those skilled in the art can derive further drawings from the accompanying drawings without any creative effort. Fig. Figure 1 shows a schematic representation of the epitaxial structure of embodiment 1. Fig. Figure 2 shows a schematic representation of the structure in the first light-emitting area of ​​embodiment 1. Fig. Figure 3 shows a schematic representation of the structure in the third light-emitting area of ​​embodiment 1. Fig. Figure 4 shows a schematic representation of the structure of the second light-emitting area surface of embodiment 1. Fig. Figure 5 shows a schematic representation of the energy band structure of the light-emitting composite area of ​​embodiment 1. Fig. Figure 6 shows a schematic representation of the structure in the first light-emitting area of ​​embodiment 2. Fig. Figure 7 shows a schematic representation of the structure in the third light-emitting area of ​​embodiment 2. Fig. Figure 8 shows a schematic representation of the structure in the second light-emitting area of ​​embodiment 2. Fig. Figure 9 shows a trend diagram of WPE (photoelectric conversion efficiency) - J (current density) of a conventional epitaxial structure for LED. Fig. Figure 10 shows the comparison of the luminance (LOP) - wavelength (WLD) of the epitaxial structure for micro-LEDs of embodiment 1 with the conventional structure at a current density of 0.5 A / cm². 3 . Fig. Figure 11 shows the comparison of the test data of WPE (photoelectric conversion efficiency) - J (current density) of the epitaxial structure for Micro-LED of embodiment 1 with the conventional structure.

[0035] Additional reference symbols in the figures: Substrate 1, U-GaN layer 2, N-GaN layer 3, stress relief layer 4, first light-emitting area 5 (including the first barrier layer 5A, the second barrier layer 5B, the third barrier layer 5C and the pot layer 5D), third light-emitting area 6 (including the first barrier layer 6A, the second barrier layer 6B, the third barrier layer 6C and the pot layer 6D), second light-emitting area 7 (including the first barrier layer 7A, the second barrier layer 7B, the third barrier layer 7C, the pot layer 7D and the fourth barrier layer 7G), PGaN layer 8, first pot layer 52D / 62D / 72D, second pot layer 52E / 62E / 72E and third pot layer 52F / 62F / 72F. Designs

[0036] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings and examples, so that the process of realization, how the invention solves the technical problems and achieves technical effects using technical means, can be fully understood and implemented accordingly. Design 1

[0037] With reference to the Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. 5 and, in accordance with the purpose of the present invention, this embodiment provides an epitaxial structure for micro-LEDs and a method for manufacturing them, comprising the following process steps: (1) A substrate 1 is provided: At least one of the following materials may be used: sapphire (Al2O3), sapphire (Al2O3) coated with AlN or SiNx, Ga2O3, with a coating of AlN or SiNxGa2O3, SiC, GaN, ZnO, Si or Ge, wherein in this embodiment preferably an AlN-coated sapphire substrate is used. (2) Epitaxial growth of the nucleation layer on substrate 1 (not shown in the figures): Preferably, the AlGaN material is selected, and the epitaxial growth method can be the MOCVD (metal-organic chemical vapor deposition), MBE (molecular beam epitaxy), CVD (chemical vapor deposition), HVPE (hydride vapor epitaxy), or PECVD (plasma-enhanced chemical vapor deposition) process, preferably the MOCVD process, but the embodiment is not limited thereto. The AlN-coated sapphire substrate is placed in a metal-organic chemical vapor deposition (MOCVD) chamber and hydrogenated to remove impurities from the substrate surface, and then the temperature is reduced to about 500°C–600°C, causing a nucleation layer with a thickness of about 20 nm to grow. (3) Epitaxial growth of the U-GaN layer 2 and the N-GaN layer 3 on the nucleation layer in succession, wherein the U-GaN layer 2 serves to reduce the lattice mismatch caused by the difference in lattice constants between the substrate and the N-GaN layer and to enhance the crystalline properties of the semiconductor layer formed on this layer, which is not limited by this embodiment. The growth of the U-GaN layer 2 proceeds in 3D + 2D mode based on the nucleation layer, first forming islands to maximize dislocation guidance and fusion, and then switching to 2D mode to form a flat surface with a growth thickness of about 1 µm to 3 µm. The N-GaN layer 3 then grows to a thickness of 1 µm to 3 µm and a doping concentration in the range of 1 × 10¹⁹ / cm². 3 up to 2.5E19 / cm 3 on. (4) The temperature is then reduced to 750°C - 950°C, wherein the stress relief layer 4 is preferably grown with the material InGaN and GaN in the form of alternating superlattice structures or combinations of these materials in order to further reduce the mismatch dislocations between the high In content material and the lower GaN material of the light-emitting layer in the subsequent steps, to relieve the stresses and to improve the crystal quality. (5) The first light-emitting region 5 is conditioned to the temperature of the barrier layer of 800°C - 900°C, whereby the first barrier layer 5A grows. In this embodiment, the first barrier layer preferably grows from the Si GaN-doped material at a growth rate of approximately 0.09 nm / s, wherein the thickness is 0.5 nm - 5 nm and the Si doping level is in the range of 1 × 10¹⁷ / cm². 3 - 1E19 / cm 3After the growth of the first barrier layer 5A is complete, the temperature is increased by 10°C to 50°C to allow the second barrier layer 5B to grow from the SiAlGaN-doped material at a growth rate of approximately 0.15 nm / s, with a thickness of approximately 3 nm to 10 nm. TMAL 2 sccm is added, and the Al content is approximately 1% to 10%, preferably 1.5% in this embodiment, and the Si doping concentration is in the range of 1E17 / cm³. 3 - 1E19 / cm 3 After the growth of the second barrier layer 5B is complete, the supply of TMAL is stopped and the temperature is reduced by 10°C - 50°C to allow the third barrier layer 5C to grow from the Si GaN-doped material at a growth rate of approximately 0.09 nm / s, with a thickness of about 0.5 nm - 5 nm and a Si doping concentration in the range of 1E17 / cm². 3 - 1E19 / cm 3After the growth of the third barrier layer 5C is complete, the supply of SiH4 is stopped and the temperature is reduced to 700°C - 800°C so that the pot layer 5D, made of InGaN, grows at a rate of approximately 0.03 nm / s with a supply of TMIN 800 sccm, with a thickness of approximately 0.5 nm - 5 nm, preferably 2 nm in this embodiment, and an average In content of approximately 18%. The number of periods in the first light-emitting region is between 1 and 5, and the material composition of the quantum pot structure is the same in each period. In this embodiment, the number of alternating stacks in the first light-emitting region is preferably 2.The band gap of the materials in the second barrier layer is greater than or equal to the band gap of the materials in the first and / or third barrier layers to effectively suppress carrier overflow and adapt the energy band structure in the light-emitting region. The variations in temperature and growth rate of the first, second, and third barrier layers aim to increase production efficiency while simultaneously improving the crystal quality of the materials in the MQW range by adjusting the growth rate of the barrier layers across different temperature ranges. (6) The third light-emitting region 6 grows by increasing the temperature to 800°C - 900°C, with the first barrier layer 6A growing first. In this embodiment, the GaN material is preferably used for the unintentionally doped layer, with a thickness of 0.5 nm - 5 nm and a growth rate of approximately 0.06 nm / s. After the growth of the first barrier layer 6A is complete, the temperature is increased by 10°C - 50°C to allow the second barrier layer 6B to grow from the SiAlGaN-doped material at a growth rate of approximately 0.09 nm / s, with a thickness of approximately 3 nm - 10 nm. TMAL 2.5 sccm is added, and the Al content is approximately 1% - 10%, preferably 2% in this embodiment, and the Si doping concentration is in the range of 1E17 / cm³. 3 - 1E19 / cm 3After the growth of the second barrier layer 6B is complete, the supply of TMAL is stopped and the temperature is reduced by 10°C - 50°C to allow the third barrier layer 6C to grow from the Si GaN-doped material at a growth rate of approximately 0.06 nm / s, with a thickness of about 0.5 nm - 5 nm and a Si doping concentration in the range of 1E17 / cm². 3 - 1E19 / cm 3After the growth of the third barrier layer 6C is complete, the supply of SiH4 is stopped and the temperature is reduced to 700°C - 800°C so that the pot layer 6D, made of InGaN, grows at a rate of approximately 0.02 nm / s with a supply of TMIN 900 sccm, with a thickness of approximately 0.5 nm - 5 nm, preferably 2 nm in this embodiment, and an average In content of approximately 19%. The number of periods in the third light-emitting region is between 0 and 5, and the material composition of the quantum pot structure is the same in each period. In this embodiment, the number of alternating stacks in the third light-emitting region is preferably chosen to be 2.The average band gap of the barrier layers in the third light-emitting region is larger than the average band gap of the barrier layers in the first light-emitting region, and the average band gap of the pot layers in the third light-emitting region is smaller than the average band gap in the first light-emitting region, in order to effectively ensure that charge carrier overflow in the light-emitting region near the P-type side is effectively suppressed, and at the same time the stress on the materials in the light-emitting region is effectively relieved, thus improving charge carrier transport and composite behavior at low current injection.The growth rate of the barrier layers in the third light-emitting region is less than or equal to the growth rate of the barrier layers in the first light-emitting region, and the growth rate of the pot layers in the third light-emitting region is less than or equal to the growth rate of the pot layers in the first light-emitting region, in order to obtain better crystal quality through the light-emitting region near the P-type side and a lower growth rate. (7) After the growth of the third light-emitting region, the second light-emitting region 7 grows due to the temperature increase to 800°C - 900°C, with the first barrier layer 7A growing first. In this embodiment, the GaN material is preferably used for the unintentionally doped layer, having a thickness of 0.5 nm - 5 nm and a growth rate of approximately 0.03 nm / s. After the growth of the first barrier layer 7A is complete, the temperature is increased by 10°C - 50°C to allow the second barrier layer 7B from the SiAlGaN-doped material to grow at a growth rate of approximately 0.05 nm / s, with a thickness of approximately 3 nm - 10 nm. TMAL 3 sccm is added, and the Al content is approximately 1% - 10%, preferably 2.5% in this embodiment, and the Si doping concentration is in the range of 1E17 / cm³. 3 - 1E19 / cm 3After the growth of the second barrier layer 7B is complete, the supply of TMAL is stopped and the temperature is reduced by 10°C to 50°C to allow the third barrier layer 7C, made of SiGaN-doped material, to grow at a rate of approximately 0.03 nm / s, with a thickness of approximately 0.5 nm to 5 nm. After the growth of the third barrier layer 7C is complete, the temperature is reduced to 700°C to 800°C to allow the pot layer 7D, made of InGaN material, to grow at a rate of approximately 0.01 nm / s with a supply of 1,000 sccm of TMIN, with a thickness of approximately 0.5 nm to 5 nm, preferably 2 nm in this embodiment, and with an average In content of approximately 20%. After the growth of the pot layer is complete, the temperature is increased to 800°C - 900°C so that the fourth barrier layer 7G made of the material GaN / AlGaN can grow at a rate of approximately 0.The growth rate is 0.5 nm / s, with a thickness of approximately 5 nm to 10 nm and an average Al content of the fourth barrier layer of approximately 5% to 50%, preferably 15% in this embodiment. The number of periods in the third light-emitting region is between 1 and 5, and the material composition of the quantum well structure is the same in each period. In this embodiment, the number of alternating stacks in the third light-emitting region is preferably chosen to be 1. As in . Fig. As shown in Figure 5, the average band gap of the barrier layers in the second light-emitting region is larger than the average band gap in the third and first light-emitting regions, and the average band gap of the pot layers in the second light-emitting region is smaller than the average band gap in the third and first light-emitting regions; and the band gap of the material of the fourth barrier layer is greater than or equal to the band gap of the materials of the first, second, and third barrier layers. The band gap of the materials of the fourth barrier layer is designed to be the largest in order to effectively prevent electrostatic overflow and to improve charge carrier transport and composite behavior at low current injection.The growth rate of the pot layers in the second light-emitting region is less than or equal to the growth rate of the pot layers in the third light-emitting region and in the first light-emitting region, in order to obtain better crystal quality through the light-emitting region near the P-type side and a lower growth rate, thereby improving the bonding behavior of the charge carriers at low current injection and thus increasing the light-emitting efficiency at low current injection. In summary, this embodiment improves charge carrier injection efficiency and interconnection efficiency by redesigning the interconnection structure of the light-emitting regions for MQWs. This effectively suppresses charge carrier overflow and enhances electron-hole wave function transitions, thereby improving charge carrier transport and interconnection behavior at low current injection. Controlling the thickness and growth rate in different MQW growth regions reduces lattice mismatch between the MQWs and the bottom layer, as well as the pot and barrier layers within the MQWs. This lowers stresses and improves the quality of MQW growth, shifting the peak efficiency towards lower current densities and enhancing illumination efficiency at low currents. (8) After the growth of the light-emitting layer, a low-temperature P-layer grows to protect the MQW from subsequent high-temperature damage and to enable a higher hole injection. (9) Subsequently, the high-temperature P-AlGaN layers and high-temperature P-GaN layers grow at elevated temperature to fill the surface. (10) Using the epiwafer of this epitaxial structure, the LED chip with a horizontal size of 19 µm * 31 µm is fabricated and tested in the chip state as shown in Fig. 10 with data shown, where the brightness compared to the conventional structure at a current density of 0.5 A / cm² 3 is improved by approximately 30%. After packaging, the photoelectric conversion efficiency (WPE) is tested as a function of the current density (J), as shown in Fig. Figure 11 shows data where the current density (J) corresponding to the peak value of the photoelectric conversion efficiency (Peak-WPE) is 4.0 A / cm². 3 to 0.7 A / cm 3 is reduced. Design 2

[0038] In this embodiment, an alternative embodiment is provided, which will be explained in more detail below.

[0039] The light-emitting area is described as follows: In contrast to embodiment 1, this embodiment is a design with multiple pot layers, which is explained in more detail below: The first light-emitting area: See Fig. 6. After the growth of the third barrier layer 5C is complete, the temperature is reduced to the temperature of the pot layer (700°C - 800°C), whereby the first pot layer 52D, made of InGaN, grows by adding 1000 sccm of TMIN at a growth rate of approximately 0.06 nm / s, with a thickness of approximately 0.3 nm - 0.8 nm. After the growth of the first pot layer is complete, the second pot layer 52E, also made of InGaN, grows at a growth rate of approximately 0.03 nm / s, with a thickness of approximately 0.5 nm - 1.5 nm. After the growth of the second pot layer is complete, the temperature is increased to the temperature of the barrier layer (800°C - 900°C), whereby the third pot layer 52F grows from the material InGaN at a growth rate of about 0.06 nm / s, with a thickness of about 0.3 nm - 0.8 nm and an average In content of about 20%.

[0040] The third light-emitting area: See Fig. 7. After the growth of the third barrier layer 6C is complete, the temperature is reduced to the temperature of the pot layer (700°C - 800°C), whereby the first pot layer 62D, made of InGaN, grows by adding 1000 sccm of TMIN at a growth rate of approximately 0.04 nm / s, with a thickness of approximately 0.3 nm - 0.8 nm. After the growth of the first pot layer is complete, the second pot layer 62E, also made of InGaN, is grown at a growth rate of approximately 0.02 nm / s, with a thickness of approximately 0.5 nm - 1.5 nm. After the growth of the second pot layer is complete, the temperature is increased to the temperature of the barrier layer (800°C - 900°C), whereby the third pot layer 62F grows from the material InGaN at a growth rate of about 0.04 nm / s, with a thickness of about 0.3 nm - 0.8 nm and an average In content of about 20%.

[0041] The second light-emitting area: See Fig.8. After the growth of the third barrier layer 7C is complete, the temperature is reduced to the temperature of the pot layer (700°C - 800°C), whereby the first pot layer 72D, made of InGaN, grows by adding 1000 sccm of TMIN at a growth rate of approximately 0.02 nm / s, with a thickness of approximately 0.3 nm - 0.8 nm. After the growth of the first pot layer 72D is complete, the second pot layer 72E, also made of InGaN, is grown at a growth rate of approximately 0.01 nm / s, with a thickness of approximately 0.5 nm - 1.5 nm. After the growth of the second pot layer 72E is complete, the temperature is increased to the temperature of the barrier layer (800°C - 900°C), whereby the third pot layer 72F grows from the material InGaN at a growth rate of about 0.01 nm / s, with a thickness of about 0.3 nm - 0.8 nm and an average In content of about 20%.

[0042] This embodiment features a multi-layer pot design to further reduce the lattice mismatch stress between the pot layer and the high-In barrier layer. This design further improves the barrier and pot layer mismatch stress within a single growth period by adjusting the pot layer growth rate across different temperature ranges, thereby enhancing MQW crystal quality and, consequently, the low-current device characteristics. embodiment 3

[0043] In this embodiment, an alternative embodiment is provided, which is explained in more detail below. The difference to embodiment 1 is that the light-emitting composite area is in the form of a combination of a first light-emitting area and a second light-emitting area. Design 4

[0044] In this embodiment, an alternative embodiment is provided, which is explained in more detail below. Epitaxial structure: substrate, nucleation layer, UGaN layer, NGaN layer, relaxation layer, P-type layer. Light-emitting regions: The difference from embodiment 1 is that the material of the fourth barrier layer in the second light-emitting region has a combination of GaN / AlGaN / AlN or a combination of their overlapping structures, such as (GaN / AlGaN / AlN) N-fold overlapping, (GaN / AlGaN) N-fold overlapping / AlN, GaN / (AlGaN / AlN) N-fold overlapping, where 1 ≤ N ≤ 20 and the average Al content is in the range of 5% to 50%.The fourth barrier layer of this embodiment has a structure of the combination of GaN / AlGaN / AlN or an overlapping combination to further reduce electron overflow, increase the overlap of the electron-hole wavefunction, thereby improving the composite behavior of the charge carriers at low current injection and thus increasing the light-emitting efficiency at low current density.

Claims

Epitaxial structure for micro-LED comprising at least one N-type layer, one light-emitting layer, and one P-type layer, wherein the light-emitting layer has a quantum well structure with n periods and the quantum well structure has a well layer and a barrier layer in each period, wherein the quantum well structure with n1 periods is defined as the first light-emitting region (5), and the quantum well structure with n2 periods is defined as the second light-emitting region (7), wherein n1 and n2 are greater than or equal to 1 and n1+n2 is less than or equal to n, wherein the first light-emitting region (5) is closer to the N-type layer than the second light-emitting region (7).wherein the average band gaps of the barrier layer materials of the two groups of light-emitting regions satisfy the following condition: the first light-emitting region is smaller than the second light-emitting region; and the average band gaps of the pot layer materials of the two groups of light-emitting regions satisfy the following condition: the first light-emitting region is greater than or equal to the second light-emitting region, wherein the quantum pot structure in each period in the second light-emitting region (7) comprises at least a first barrier layer (7A), a second barrier layer (7B), a third barrier layer (7C), a pot layer (7D), and a fourth barrier layer (7G), wherein the second barrier layer (7B) is located between the first barrier layer (7A) and the third barrier layer (7C), and the fourth barrier layer (7G) is located behind the pot layer (7D).wherein in the second light-emitting region (7) the band gap of the materials of the second barrier layer (7B) of each quantum well structure is larger than the band gap of the materials of the first barrier layer (7A) and the third barrier layer (7C), and the band gap of the materials of the fourth barrier layer (7G) is larger than the band gap of the materials of the first barrier layer, the second barrier layer and the third barrier layer. Epitaxial structure for micro-LED according to claim 1, wherein the quantum well structure in each period in the first light-emitting region (5) comprises at least a first barrier layer (5A), a second barrier layer (5B), a third barrier layer (5C) and a well layer (5D), wherein the second barrier layer (5B) of the quantum well structure in each period in the first light-emitting region (5) is arranged between the first barrier layer (5A) of the quantum well structure in each period in the first light-emitting region (5) and the third barrier layer (5C) of the quantum well structure in each period in the first light-emitting region (5), and in the first light-emitting region (5) the band gap of the materials of the second barrier layer (5B) of each quantum well structure is larger than the band gap of the materials of the first barrier layer (5A) and the third barrier layer (5C). Epitaxial structure for micro-LED according to claim 1 or 2, wherein the thicknesses of the first barrier layer, the second barrier layer, the third barrier layer and the fourth barrier layer are in the range of 1 nm to 100 nm; and the thickness of the pot layer is in the range of 0.1 nm to 10 nm. Epitaxial structure for micro-LED according to claim 1 or 2, wherein the total thickness of the first barrier layer, the second barrier layer and the third barrier layer to the thickness of the pot layer in the quantum pot structure in each period is in a ratio of 5:1 to 20:

1. Epitaxial structure for micro-LED according to claim 1, wherein the thickness of the fourth barrier layer to the thickness of the pot layer is in a ratio of 5:1 to 20:

1. Epitaxial structure for micro-LED according to claim 1 or 2, wherein in the quantum well structure in each period the thickness of the second barrier layer is greater than the thickness of the first barrier layer and the third barrier layer. Epitaxial structure for micro-LED according to claim 1, wherein in the quantum well structure in each period in the second light-emitting region (7) the thickness of the fourth barrier layer (7G) is greater than the thickness of the first barrier layer (7A) and the third barrier layer (7C). Epitaxial structure for micro-LED according to claim 1 or 2, wherein in the two groups of light-emitting regions the first barrier layer, the second barrier layer and the third barrier layer are fully or partially n-type doped and the fourth barrier layer is unintentionally doped. Epitaxial structure for micro-LED according to claim 8, wherein in the two groups of light-emitting regions the first barrier layer, the second barrier layer and the third barrier layer are fully or partially n-type doped and the concentration of the n-type doping is in the range of 1E17 / cm3- 1E19 / cm3. Epitaxial structure for micro-LED according to claim 1, wherein the first light-emitting region (5) has a period number of 1 to 5 and the second light-emitting region (7) has a period number of 1 to 5. Epitaxial structure for micro-LED according to claim 1 or 2, wherein the pot layer consists of the material AlxInyGa1-x-yN, and the first barrier layer, the second barrier layer, the third barrier layer and the fourth barrier layer consist of the material AlpInqGa1-p-qN, wherein the conditions 0 ≤ x < p < 1; 0 ≤ q < y < 1 apply in the quantum pot structure in each period. Epitaxial structure for micro-LED according to claim 1, wherein the average percentage of Al content in the barrier layer materials in the two groups of light-emitting areas satisfies the following condition: the first light-emitting area (5) is smaller than the second light-emitting area (7); that the average percentages of In content in the pot layer materials in the two groups of light-emitting areas satisfy the following condition: the first light-emitting area (5) is smaller than or equal to the second light-emitting area (7). Epitaxial structure for micro-LED according to claim 1 or 2, wherein in each quantum well structure the average percentage of Al content in the material of the second barrier layer is greater than the average percentage of Al content in the materials of the first barrier layer and the third barrier layer. Epitaxial structure for micro-LED according to claim 1, wherein in the quantum well structure in each period in the second light-emitting region (7) the average percentage of Al content in the material of the fourth barrier layer (7G) is greater than the average percentage of Al content in the materials of the first barrier layer (7A), the second barrier layer (7B) and the third barrier layer (7C). Epitaxial structure for micro-LED according to claim 1, wherein the light-emitting region further comprises a third light-emitting region (6), wherein the third light-emitting region (6) has a quantum well structure with n3 periods and is arranged between the first light-emitting region (5) and the second light-emitting region (7), wherein the band gap of the barrier layer in the third light-emitting region lies between that in the first light-emitting region (6) and in the second light-emitting region (7); and the band gap of the well layer in the third light-emitting region lies between that in the first light-emitting region (5) and in the second light-emitting region (7). Epitaxial structure for micro-LED according to claim 15, wherein the average percentage of Al content of the barrier layer in the third light-emitting region is between that in the first light-emitting region (5) and in the second light-emitting region (7); and the average percentage of In content of the pot layer in the third light-emitting region is between that in the first light-emitting region (5) and in the second light-emitting region (7). Epitaxial structure for micro-LED according to claim 15, wherein the third light-emitting region comprises a first barrier layer (6A), a second barrier layer (6B), a third barrier layer (6C) and a pot layer (6D), wherein the band gap of the materials of the second barrier layer in the third light-emitting region is larger than the band gap of the materials of the first barrier layer (6A) and the third barrier layer (6C). Epitaxial structure for micro-LED according to claim 17, wherein the thickness of the second barrier layer (6B) in the third light-emitting region is greater than the thickness of the first barrier layer (6A) and the third barrier layer (6C). Epitaxial structure for micro-LED according to claim 17, wherein the thicknesses of the first barrier layer (6A), the second barrier layer (6B) and the third barrier layer (6C) in the third light-emitting region are in the range of 1 nm to 100 nm; and the thickness of the pot layer is in the range of 0.1 nm to 10 nm. Epitaxial structure for micro-LED according to claim 17, wherein in the third light-emitting region the total thickness of the first barrier layer (6A), the second barrier layer (6B) and the third barrier layer (6C) is in a ratio of 5:1 to 20:1 to the thickness of the pot layer. Epitaxial structure for micro-LED according to claim 17, wherein in the third light-emitting region the first barrier layer (6A), the second barrier layer (6B) and the third barrier layer (6C) are fully or partially n-type doped, wherein the concentration of the n-doping is in the range of 1E17 / cm3- 1E19 / cm3. Epitaxial structure for micro-LED according to claim 15, wherein the third light-emitting region (6) has a period number of 1 to 5. Epitaxial structure for micro-LED according to claim 17, wherein the pot layer in the third light-emitting region (6D) consists of the material AlxInyGa1-x-yN; and the first barrier layer (6A), the second barrier layer (6B) and the third barrier layer (6C) consist of the material AlpInqGa1-p-qN, wherein the conditions 0 ≤ x < p < 1; 0 ≤ q < y < 1 apply. Epitaxial structure for micro-LED according to claim 17, wherein in each quantum well structure in the third light-emitting region (6) the average percentage of Al content in the materials of the second barrier layer (6B) is greater than the average percentage of Al content in the materials of the first barrier layer (6A) and the third barrier layer (6C). Method, wherein an epitaxial structure for a micro-LED according to any one of claims 1 to 24 is produced, the method comprising the following steps: (1) A substrate (1) is provided; (2) A nucleation layer, an N-type layer and a light-emitting layer grow on the substrate; (3) A P-type layer grows. Method for producing an epitaxial structure for micro-LEDs according to claim 25, wherein the average growth rate of the barrier layer in the first light-emitting region is greater than the average growth rate of the barrier layer in the second light-emitting region. Method for producing an epitaxial structure for micro-LED according to claim 25, wherein the average growth rate of the pot layer in the first light-emitting region (5D) is greater than the average growth rate of the pot layer in the second light-emitting region (7D). Method for producing an epitaxial structure for micro-LED according to claim 25, wherein the average growth rate of the first barrier layer and the third barrier layer in each quantum well structure is less than or equal to the average growth rate of the second barrier layer. Method for producing an epitaxial structure for micro-LEDs according to claim 25, wherein the growth rate of the barrier layer is in the range of 0.01 nm / s to 1 nm / s; the growth rate of the pot layer is in the range of 0 nm / s to 0.1 nm / s. Method for producing an epitaxial structure for micro-LEDs according to claim 25, wherein the growth temperature of the barrier layer is in the range of 700°C - 950°C; and the growth temperature of the pot layer is in the range of 700°C - 900°C. Method for producing an epitaxial structure for micro-LEDs according to claim 25, wherein the growth of the barrier layers and the pot layer in the light-emitting composite area has a continuous or interrupted growth. Micro-LED, micro-LED, wherein it has the epitaxial structure according to any one of the preceding claims 1 to 24. Micro-LED according to claim 32, wherein the micro-LED has a horizontal dimension between 1 µm * 1 µm - 300 µm * 300 µm. Light-emitting device comprising the micro-LED according to claim 32.

Images