A method for fabricating a micro LED chip and its epitaxial layer

Abstract

This application discloses a micro LED chip and a method for fabricating its epitaxial layer. The micro LED chip includes an epitaxial layer, which, from bottom to top, comprises a first semiconductor layer, an active layer, and a second semiconductor layer. The active layer is doped with one or more doping elements, which are doped in a combination of uniform doping and gradient doping or in a spaced-area doping manner. The method for fabricating the epitaxial layer in the micro LED chip provided in this application includes doping the active layer with one or more doping elements through a combination of uniform doping and gradient doping; or doping the active layer with one or more doping elements through spaced-area doping. This micro LED chip can control the stress of the epitaxial layer and the wavelength of light emission, improving the internal quantum efficiency and light extraction efficiency of the active layer, thereby improving the external quantum efficiency and brightness uniformity of the micro LED display chip.

Description

Technical Field

[0001] This application relates to the semiconductor field, and more specifically to a method for fabricating micro LED chips and their epitaxial layers. Background Technology

[0002] Micro LEDs (Micro Light Emitting Diodes), also known as micro LEDs or μ-LEDs, are micro LED display chips comprising an array of micro LEDs with multiple single-pixel elements. The distance between the LED pixels in the array is on the order of 100 nanometers to 100 micrometers, and each micro LED pixel is self-emissive. Micro LEDs typically include an epitaxial layer, which further comprises an N-type semiconductor layer, a P-type semiconductor layer, and an intermediate layer located between the N-type and P-type semiconductor layers; this intermediate layer is called the active layer.

[0003] Micro-LEDs are becoming increasingly important due to their potential applications, including self-emitting microdisplays, visible light communication, and optogenetics. They offer superior output performance compared to conventional LEDs due to their better strain relaxation, light extraction efficiency, and uniform current spread. Micro-LEDs also exhibit several advantages over conventional LEDs, such as improved thermal performance, faster response times, a wider operating temperature range, higher resolution, a wider color gamut, higher contrast, lower power consumption, and operability at higher current densities.

[0004] Micro-LED displays, based on micro-LEDs, are much smaller than traditional LCD (Liquid Crystal Display) and OLED (Organic Light-Emitting Diode) displays, and are therefore used in automotive displays, wearable products, smartwatches, VR / AR, and other fields. Typically, micro-LED arrays are fabricated by etching III-V epitaxial layers to form multiple mesa.

[0005] Improving the luminous efficiency of existing micro LED display chips is a problem that urgently needs to be solved. Summary of the Invention

[0006] To address one or more of the aforementioned technical problems, this application provides a method for fabricating a micro LED chip and its epitaxial layer.

[0007] This application provides a micro LED chip, including an epitaxial layer, which comprises, from bottom to top, a first semiconductor layer, an active layer, and a second semiconductor layer, wherein one or more doping elements are doped in the active layer in a combination of uniform doping and gradient doping or in a spaced doping manner.

[0008] This application also provides a method for preparing the epitaxial layer of the above-mentioned micro LED chip, the method comprising: providing a substrate; growing a buffer layer on the substrate; growing a first semiconductor layer on the buffer layer; growing an active layer on the first semiconductor layer; and growing a second semiconductor layer on the active layer; growing the active layer on the first semiconductor layer comprises doping the active layer with one or more doping elements by a combination of uniform doping and gradient doping; or doping the active layer with one or more doping elements by a spaced doping method.

[0009] The micro LED chip provided in this application can regulate the stress of the epitaxial layer and the wavelength of light emission, thereby improving the internal quantum efficiency and light extraction efficiency of the active layer, and thus improving the external quantum efficiency and brightness uniformity of the micro LED chip. Attached Figure Description

[0010] The above and other objects, features and advantages of this disclosure will become more apparent from the more detailed description of exemplary embodiments thereof taken in conjunction with the accompanying drawings, wherein like reference numerals generally denote like parts.

[0011] Figure 1 This is a schematic diagram of the epitaxial structure of the epitaxial layer for a micro LED chip according to some embodiments of this application;

[0012] Figures 2A to 2C The diagram illustrates the relationship between doping concentration and active layer growth height in different embodiments combining uniform doping and gradient doping according to some embodiments of this application.

[0013] Figure 3A and Figure 3B A schematic diagram showing the relationship between doping concentration and active layer growth height in different embodiments of spacer doping according to some embodiments of this application is shown.

[0014] Figure 4 This is a flowchart illustrating the fabrication of the epitaxial layer of a micro LED chip according to some embodiments of this application;

[0015] Figures 5A to 5C A flowchart illustrating a doping method combining uniform doping and gradient doping according to some embodiments of this application;

[0016] Figure 6 This is a flowchart of a method for spaced-doped active layers according to some embodiments of this application. Detailed Implementation

[0017] Preferred embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0018] Some embodiments of this application provide a micro LED chip that can effectively improve internal quantum efficiency and light extraction efficiency, thereby improving the external quantum efficiency of the micro LED chip.

[0019] Figure 1 This is a schematic diagram of the epitaxial structure of an epitaxial layer for a micro LED chip according to some embodiments of this application. For example... Figure 1As shown, the epitaxial structure 100 includes, from bottom to top, a substrate 110, a buffer layer 120, a first semiconductor layer 130, an active layer 140, and a second semiconductor layer 150. In some embodiments, the substrate 110 is a substrate with a predetermined crystal orientation, such as a (100) biased crystal orientation. <111> A is an N-type GaAs substrate with a temperature range of 2 to 15 degrees. In some embodiments, the buffer layer 120 is a GaAs buffer layer with a thickness of 100 nanometers to 500 nanometers. In some embodiments, the first semiconductor layer 130 is an N-type semiconductor layer, including one or more of the following structures: an etching stop layer, an ohmic contact layer, a confinement layer, or a waveguide layer. The etching stop layer can be made of AlGaInP or AlInP, the ohmic contact layer can be made of AlGaInP, AlInP, or GaAs, the confinement layer can be made of AlGaInP or AlInP, and the waveguide layer can be made of AlGaInP or AlInP. In some embodiments, the thickness of the first semiconductor layer 130 ranges from 200 nanometers to 800 nanometers. In some embodiments, the active layer 140 is a multiple quantum well (MQW) structure, formed by overlapping multiple quantum barrier layers 1402 and quantum well layers 1401. The active layer 140 is doped with one or more doping elements, such as Mg, As, Sb, Fe, Zn, Si, Te, Bi, etc. In some embodiments, the second semiconductor layer 150 is a P-type semiconductor layer, including one or more of the following structures: a waveguide layer, a confinement layer, a transition layer, a window layer, or an ohmic contact layer. The waveguide layer may be made of AlGaInP or AlInP, the confinement layer may be made of AlGaInP or AlInP, the transition layer may be made of AlGaInP or AlInP, the window layer may be made of GaP, AlInP, or AlGaAs, and the ohmic contact layer may be made of GaP, AlInP, or AlGaAs. In some embodiments, the total thickness of the second semiconductor layer 150 ranges from 200 nm to 800 nm. In some embodiments, the thicknesses of the first semiconductor layer 130, the active layer 140, and the second semiconductor layer 150 range from 500 nm to 2000 nm. In some embodiments, the ratio of the thickness of the active layer 140 to the total thickness of the epitaxial layer 100 ranges from 3% to 50%.

[0020] In some embodiments, one or more doping elements are doped in the active layer 140 in a combination of uniform doping and gradient doping.

[0021] Figures 2A to 2C The diagram illustrates the relationship between doping concentration and active layer growth height in different embodiments combining uniform doping and gradient doping according to some embodiments of this application. Figures 2A to 2C The schematic diagram of the epitaxial layer of the micro LED chip shown can be regarded as... Figure 1The extensional structure 100 is placed after rotating 90 degrees clockwise. See also... Figure 2A In some embodiments, the active layer 140 includes a uniformly doped region 141A and a gradient-doped region 142A. Within the uniformly doped region 141A, the doping concentration of the dopant element (e.g., dopant element A or dopant element B) is a first concentration, which varies by no more than 20%, i.e., remains relatively constant. Within the gradient-doped region 142A, the doping concentration of the dopant element (e.g., dopant element A or dopant element B) is a second concentration, which varies with the height of the active layer 140, i.e., varies with the growth height of the active layer 140. The uniformly doped region 141A is located near the first semiconductor layer 130, and the gradient-doped region 142A is located near the second semiconductor layer 150. The initial concentration of the second concentration is the same as the first concentration. That is, the dopant element is doped at the first concentration within the uniformly doped region 141A of the active layer. When doping reaches point P, the concentration increases or decreases within the gradient-doped region 142A with the first concentration as the active layer grows. In this embodiment, the region from the starting point of the active layer 140 to point P is a uniformly doped region, and the region continuing to grow from point P to the ending position of the active layer 140 is a gradually doped region. In some embodiments, point P can be any position within the active layer 140. In some embodiments, point P is the middle position of the active layer.

[0022] In some embodiments, such as for dopant element A, the second concentration increases with increasing height of the active layer in the gradient doping region 142A. In this embodiment, the first concentration ranges from 2E to 16 cm⁻¹. -3 Up to 5E17 cm -3 The final concentration range for the second concentration is 5E 17 cm⁻¹. -3 Up to 2E 18 cm -3 In some embodiments, the ratio of the final concentration of the second concentration to the initial concentration of the second concentration (i.e., the first concentration) is greater than 1.5.

[0023] In some embodiments, such as for dopant element B, the second concentration decreases with increasing height of the active layer in the gradient doping region 142A. In this embodiment, the first concentration ranges from 5E17 cm⁻¹. -3 Up to 2E18 cm -3 The final concentration range for the second concentration is 1E17 cm⁻¹. -3 Up to 5E17 cm -3 In some embodiments, the ratio of the initial concentration of the second concentration (i.e., the first concentration) to the final concentration of the second concentration is greater than 1.5.

[0024] In some embodiments, the dopant element further dops the second semiconductor layer to a final concentration of the second concentration. In some embodiments, doping is stopped after the active layer growth is complete.

[0025] See Figure 2B In some embodiments, the active layer 140 includes a gradient-doped region 141B and a uniformly doped region 142B. Within the gradient-doped region 141B, the doping concentration of the dopant element (e.g., dopant element A or dopant element B) is a first concentration, which varies with the height of the active layer 140, i.e., with the growth height of the active layer 140. Within the uniformly doped region 142B, the doping concentration of the dopant element (e.g., dopant element A or dopant element B) is a second concentration, and the variation amplitude of this second concentration in the uniformly doped region 142B does not exceed 20%, i.e., it is relatively fixed. The gradient-doped region 141B is located near the first semiconductor layer 130, and the uniformly doped region 141B is located near the second semiconductor layer 150. The final concentration of the first concentration is the second concentration. That is, the dopant element is doped at the first concentration within the gradient doping region 141B of the active layer. The doping concentration increases or decreases with the height of the active layer. When doping reaches point Q, the concentration at point Q is used as the second concentration for doping within the uniform doping region 142B. The variation amplitude of this second concentration in the uniform doping region 142B does not exceed 20%, i.e., it is relatively fixed. In this embodiment, the region from the starting point of the active layer 140 to point Q is the gradient doping region, and the region from point Q to the end of the active layer 140 is the uniform doping region. In some embodiments, the position of point Q can be any position within the active layer 140. In some embodiments, the position of point Q is the middle position of the active layer.

[0026] In some embodiments, such as for dopant element A, the first concentration in the gradient doped region 141B increases with the height of the active layer. In this embodiment, the first concentration ranges from 2E to 16 cm⁻¹. -3 Up to 5E17 cm -3 The final concentration range of the first concentration is 5E 17 cm⁻¹. -3 Up to 2E 18 cm -3 In some embodiments, the ratio of the final concentration of the first concentration (i.e., the second concentration) to the initial concentration of the first concentration is greater than 1.5.

[0027] In some embodiments, such as for dopant element B, the first concentration decreases with increasing height of the active layer in the gradient doping region 141B. In this embodiment, the first concentration ranges from 5E17 cm⁻¹. -3 Up to 2E18 cm -3 The final concentration range of the first concentration is 1E17 cm⁻¹. -3 Up to 5E17 cm-3 In some embodiments, the ratio of the initial concentration of the first concentration to the final concentration of the first concentration (i.e., the second concentration) is greater than 1.5.

[0028] In some embodiments, the dopant element further dops the second semiconductor layer at a second concentration. In some embodiments, the doping of the dopant element is stopped after the active layer growth is completed.

[0029] See Figure 2C In some embodiments, the active layer 140 includes a first uniformly doped region 141C, a gradient doped region 142C, and a second uniformly doped region 142C. Within the first uniformly doped region 141C, the doping concentration of the dopant element (e.g., dopant element A or dopant element B) is a first concentration, and the variation range of this first concentration within the first uniformly doped region 141C does not exceed 20%, i.e., it is relatively fixed. Within the gradient doped region 142C, the doping concentration of the dopant element (e.g., dopant element A or dopant element B) is a second concentration, and this second concentration varies with the height of the active layer 140, i.e., it varies with the growth height of the active layer 140. Within the second uniformly doped region 143C, the doping concentration of the dopant element (e.g., dopant element A or dopant element B) is a third concentration, and the variation range of this third concentration within the second uniformly doped region 143C does not exceed 20%, i.e., it is relatively fixed. The first uniformly doped region 141C is close to the first semiconductor layer 130, the second uniformly doped region 143C is close to the second semiconductor layer 150, and the gradient doped region 142C is between the first uniformly doped region 141C and the second uniformly doped region 143C. The initial concentration of the second concentration is the concentration of the first concentration, that is, the dopant element is doped at the first concentration in the first region 141C with the active layer. When doping reaches point P, the concentration increases or decreases with the growth height of the active layer 140, starting from the first concentration. The final concentration of the second concentration is the third concentration, that is, the dopant element is doped at the second concentration in the gradient doped region 142C of the active layer. The doping concentration increases or decreases with the height of the active layer. When doping reaches point Q, the concentration at point Q is used as the third concentration in the second uniformly doped region 143C. The variation amplitude of the third concentration in the second uniformly doped region 143C does not exceed 20%, that is, it is relatively fixed. In this embodiment, the region from the starting point of the active layer 140 to point P is the first uniformly doped region, the region growing from point P to point Q is the gradient doped region, and the region continuing to grow from point Q to the termination position of the active layer 140 is the second uniformly doped region. In some embodiments, point P can be any position within the active layer 140, and point Q can be any position after point P. In some embodiments, the heights of the first and second uniformly doped regions are equal, that is, the distance from the starting position of the active layer to point P is equal to the distance from point Q to the termination position of the active layer.

[0030] In some embodiments, such as for dopant element A, the second concentration increases with increasing height of the active layer in the gradient doping region 142C. In this embodiment, the first concentration ranges from 2E to 16 cm⁻¹. -3 Up to 5E17 cm -3 The third concentration range is 5E 17 cm⁻¹ -3 Up to 2E 18 cm -3 In some embodiments, the ratio of the third concentration to the first concentration is greater than 1.5.

[0031] In some embodiments, such as for dopant element B, the second concentration decreases with increasing height of the active layer in the gradient doping region 142C. In this embodiment, the first concentration ranges from 5E17 cm⁻¹. -3 Up to 2E18 cm -3 The third concentration range is 1E17 cm⁻¹ -3 Up to 5E17 cm -3 In some embodiments, the ratio of the first concentration to the third concentration is greater than 1.5.

[0032] In some embodiments, the dopant element further dops the second semiconductor layer at a third concentration. In some embodiments, doping is stopped after the active layer growth is complete.

[0033] By combining uniform doping and gradient doping to dope the active layer, the internal quantum efficiency and light extraction efficiency of the active layer can be improved, thereby improving the external quantum efficiency and brightness uniformity of the micro LED display chip.

[0034] In some embodiments, one or more doping elements are doped in the active layer 140 by spacer doping.

[0035] Figure 3A and Figure 3B A schematic diagram showing the relationship between doping concentration and active layer growth height in different embodiments of spacer doping according to some embodiments of this application is illustrated. Figure 3A and Figure 3B The schematic diagram of the epitaxial layer of the micro LED chip shown can be regarded as... Figure 1 The extensional structure is rotated 90 degrees clockwise and placed. See also Figure 3A and Figure 3BThe active layer 140 includes a plurality of quantum well layers W and a plurality of quantum barrier layers B arranged at intervals between each other. In some embodiments, the number of quantum well layers is N, and the number of quantum barrier layers is N+1, where N is a positive integer, meaning there is one more quantum barrier layer than quantum well layer. The layers closest to the first semiconductor layer 130 and the second semiconductor layer 150 are all quantum barrier layers B. In some embodiments, the total number of quantum barrier layers and quantum well layers does not exceed 50. The doping concentration of the one or more doping elements in the quantum well layers is different from the doping concentration of the doping element in the quantum barrier layers.

[0036] See Figure 3A The doping concentration of the dopant element in the quantum well layer W is a fourth concentration C1, and the doping concentration of the dopant element in the quantum barrier layer B is a fifth concentration C2. As shown in the figure, the dopant element is doped at the fourth concentration C1 at the starting position of growth in the quantum well layer W, and at the fifth concentration C2 near the starting position of growth in the quantum barrier layer B. In this embodiment, the fourth concentration C1 is greater than the fifth concentration C2, that is, for this dopant element, it is doped at a higher concentration in the quantum well layer W and at a lower concentration in the quantum barrier layer B, so as to achieve spaced doping in the active layer 140. In some embodiments, the range of the fourth concentration C1 is 1E17 cm⁻¹. -3 Up to 1E18 cm -3 The fifth concentration of C2 ranges from 5E16 cm⁻¹. -3 Up to 2E17cm -3 The ratio of the fourth concentration C1 to the fifth concentration C2 (i.e., C1 / C2) is greater than 1.5.

[0037] In some embodiments, the quantum well layer W further includes a buffer region, wherein the doping concentration of the dopant element in the buffer region of the quantum well layer W is a fifth concentration C2, which is the same as the doping concentration in the quantum barrier layer B. See also Figure 3A Taking quantum well layer 1401 as an example, quantum well layer 1401 grows from position a to position b, ending at which point the growth of the next quantum barrier layer B begins. Starting from position a, a dopant element is doped into quantum well layer 1401 at a fourth concentration C1 until quantum well layer 1401 grows to position c. From position c, the dopant element is then doped into quantum well layer 1401 at a fifth concentration C2, and this fifth concentration C2 is continued for quantum barrier layer B. The region where quantum well layer 1401 grows from position c to position b is the buffer region. In some embodiments, the thickness of the buffer region is one-third to four-fifths of the thickness of its corresponding quantum well layer, that is, the distance from point c to point b is one-third to four-fifths of the distance from point a to point b.

[0038] See Figure 3BThe doping concentration of the dopant element in the quantum well layer W is a fourth concentration C1, and the doping concentration of the dopant element in the quantum barrier layer B is a fifth concentration C2. As shown in the figure, the dopant element is doped at the fifth concentration C2 at the starting position of the growth of the quantum barrier layer B, and at the fourth concentration C1 near the starting position of the growth of the quantum well layer W. In this embodiment, the fifth concentration C2 is greater than the fourth concentration C1, that is, for this dopant element, it is doped at a higher concentration in the quantum barrier layer B and at a lower concentration in the quantum well layer W, thereby achieving spaced doping in the active layer 140. In some embodiments, the fourth concentration C1 ranges from 5E16 cm⁻¹. -3 Up to 2E17 cm -3 The fifth concentration of C2 ranges from 1E17 cm⁻¹. -3 Up to 2E18cm -3 The ratio of the fifth concentration C2 to the fourth concentration C1 (i.e., C2 / C1) is greater than 1.5.

[0039] In some embodiments, the quantum barrier layer B further includes a buffer region, wherein the doping concentration of the dopant element in the buffer region of the quantum barrier layer B is a fourth concentration C1, which is the same as the doping concentration in the quantum well layer W. See also Figure 3B Taking quantum barrier layer 1402 as an example, quantum barrier layer 1402 grows from position a to position b, ending at which point the growth of the next quantum well layer W begins. Starting from position a, a dopant element is doped into quantum barrier layer 1402 at a fifth concentration of C2 until quantum barrier layer 1402 grows to position c. From position c, the dopant element is then used to dope quantum barrier layer 1402 at a fourth concentration of C1, and continues to dope quantum well layer W at the fourth concentration of C1. The region where quantum barrier layer 1402 grows from position c to position b is the buffer region. In some embodiments, the thickness of the buffer region is one-third to four-fifths of the thickness of the corresponding quantum barrier layer, that is, the distance from point c to point b is one-third to four-fifths of the distance from point a to point b. By doping the active layer in a spaced-out manner, stress or wavelength can be controlled.

[0040] The micro LED chip provided in this application can regulate the stress of the epitaxial layer and the wavelength of light emission, improve the internal quantum efficiency and light extraction efficiency of the active layer, and thus improve the external quantum efficiency and brightness uniformity of the micro LED display chip.

[0041] This application also provides a method for preparing the epitaxial layer of the above-mentioned micro LED chip. Figure 4 This is a flowchart illustrating a method for fabricating an epitaxial layer of a microLED chip according to some embodiments of this application. Figure 4 As shown, the method 400 for preparing the epitaxial layer of a micro LED chip includes steps 402 to 410.

[0042] Step 402, providing a substrate. In some embodiments, the substrate is a substrate with a predetermined crystal orientation, such as a (100) biased crystal orientation. <111> A is an N-type GaAs substrate with a temperature range of 2 to 15 degrees.

[0043] Step 404: Grow a buffer layer on the substrate. In some embodiments, the buffer layer is a GaAs buffer layer with a thickness of 100 nanometers to 500 nanometers.

[0044] Step 406: Grow a first semiconductor layer on the buffer layer. Specifically, grow the first semiconductor layer on the side of the buffer layer away from the substrate. In some embodiments, the first semiconductor layer is an N-type semiconductor layer, including one or more of the following structures: an etching stop layer, an ohmic contact layer, a confinement layer, or a waveguide layer. The etching stop layer may be made of AlGaInP or AlInP, the ohmic contact layer may be made of AlGaInP, AlInP, or GaAs, the confinement layer may be made of AlGaInP or AlInP, and the waveguide layer may be made of AlGaInP or AlInP. In some embodiments, the thickness of the first semiconductor layer ranges from 200 nanometers to 800 nanometers.

[0045] Step 408: An active layer is grown on the first semiconductor layer. In some embodiments, the active layer is a multiple quantum well (MQW) structure, formed by overlapping multiple quantum barrier layers and quantum well layers. The active layer 140 is doped with one or more doping elements, such as Mg, As, Sb, Fe, Zn, Si, Te, Bi, etc.

[0046] Step 410: Growing a second semiconductor layer on the active layer. In some embodiments, the second semiconductor layer is a P-type semiconductor layer, including one or more of the following structures: a waveguide layer, a confinement layer, a transition layer, a window layer, or an ohmic contact layer. The waveguide layer may be made of AlGaInP or AlInP, the confinement layer may be made of AlGaInP or AlInP, the transition layer may be made of AlGaInP or AlInP, the window layer may be made of GaP, AlInP, or AlGaAs, and the ohmic contact layer may be made of GaP, AlInP, or AlGaAs. In some embodiments, the thickness of the second semiconductor layer ranges from 200 nanometers to 800 nanometers.

[0047] In some embodiments, the total thickness of the first semiconductor layer, the active layer, and the second semiconductor layer ranges from 500 nanometers to 2000 nanometers. In some embodiments, the ratio of the thickness of the active layer to the total thickness of the epitaxial layer ranges from 3% to 50%.

[0048] In some embodiments, step 408 further includes doping the active layer with one or more doping elements. In some embodiments, the one or more doping elements are doped in the active layer by a combination of uniform doping and gradient doping. Figures 5A to 5C This is a flowchart illustrating a doping method combining uniform doping and gradient doping according to some embodiments of this application. See also... Figure 5A The active layer doping method 500A includes steps 502A and 504A.

[0049] Step 502A: Doping one or more doping elements at a first concentration within the uniformly doped region. (Combined with...) Figure 2A In some embodiments, the active layer 140 includes a uniformly doped region 141A and a gradient doped region 142A. In the uniformly doped region 141A, the doping concentration of the doping element (e.g., doping element A or doping element B) is a first concentration, and the variation amplitude of the first concentration in the uniformly doped region 141A does not exceed 20%, that is, it is relatively fixed.

[0050] Step 504A: Doping one or more doping elements at a second concentration in the gradient doping region 142A. Within the gradient doping region 142A, the doping concentration of the doping element (e.g., doping element A or doping element B) is the second concentration, which varies with the height of the active layer 140, i.e., varies with the growth height of the active layer 140.

[0051] According to method 500A, the uniformly doped region 141A is close to the first semiconductor layer 130, and the gradient-doped region 142A is close to the second semiconductor layer 150. Uniform doping is performed first, followed by gradient doping. The initial concentration of the second concentration is the same as the first concentration; that is, the dopant element is doped at the first concentration within the uniformly doped region 141A of the active layer. When doping reaches point P, the concentration increases or decreases within the gradient-doped region 142A with the first concentration as the active layer grows. In this embodiment, the region from the starting point of the active layer 140 to point P is the uniformly doped region, and the region from point P to the end of the active layer 140 is the gradient-doped region.

[0052] In some embodiments, such as for dopant element A, the second concentration increases with increasing height of the active layer in the gradient doping region 142A. In this embodiment, the first concentration ranges from 2E to 16 cm⁻¹. -3 Up to 5E17 cm -3 The final concentration range for the second concentration is 5E 17 cm⁻¹. -3 Up to 2E 18 cm -3 In some embodiments, the ratio of the final concentration of the second concentration to the initial concentration of the second concentration (i.e., the first concentration) is greater than 1.5.

[0053] In some embodiments, such as for dopant element B, the second concentration decreases with increasing height of the active layer in the gradient doping region 142A. In this embodiment, the first concentration ranges from 5E17 cm⁻¹. -3 Up to 2E18 cm -3 The final concentration range for the second concentration is 1E17 cm⁻¹. -3 Up to 5E17 cm -3 In some embodiments, the ratio of the initial concentration of the second concentration (i.e., the first concentration) to the final concentration of the second concentration is greater than 1.5.

[0054] In some embodiments, the dopant element further dops the second semiconductor layer to a final concentration of the second concentration. In some embodiments, doping is stopped after the active layer growth is complete.

[0055] See Figure 5B The active layer doping method 500B includes steps 502B and 504B.

[0056] Step 502B involves doping one or more doping elements at a second concentration within the gradient doping region. (Combined with...) Figure 2B In some embodiments, the active layer 140 includes a gradient doped region 141B and a uniform doped region 142B. In the gradient doped region 141B, the doping concentration of the doping element (e.g., doping element A or doping element B) is a first concentration, which varies with the height of the active layer 140, that is, with the growth height of the active layer 140.

[0057] Step 504B: Doping one or more doping elements at a first concentration within the uniform doping region 142B. Within the uniform doping region 142B, the doping concentration of the doping element (e.g., doping element A or doping element B) is a second concentration, and the variation range of this second concentration within the uniform doping region 142B does not exceed 20%, i.e., it is relatively fixed.

[0058] According to method 500B, the gradient-doped region 141B is close to the first semiconductor layer 130, and the uniformly doped region 141B is close to the second semiconductor layer 150. Gradient doping is performed first, followed by uniform doping. The final concentration of the first concentration is the second concentration, that is, the dopant element is doped in the gradient-doped region 141B of the active layer at the first concentration. The doping concentration increases or decreases with the height of the active layer. When doping reaches point Q, the concentration at point Q is used as the second concentration in the uniformly doped region 142B. The variation amplitude of this second concentration in the uniformly doped region 142B does not exceed 20%, that is, it is relatively fixed. In this embodiment, the region from the starting point of the active layer 140 to point Q is the gradient-doped region, and the region from point Q to the end position of the active layer 140 is the uniformly doped region.

[0059] In some embodiments, such as for dopant element A, the first concentration in the gradient doped region 141B increases with the height of the active layer. In this embodiment, the first concentration ranges from 2E to 16 cm⁻¹. -3 Up to 5E17 cm -3 The final concentration range of the first concentration is 5E 17 cm⁻¹. -3 Up to 2E 18 cm -3 In some embodiments, the ratio of the final concentration of the first concentration (i.e., the second concentration) to the initial concentration of the first concentration is greater than 1.5.

[0060] In some embodiments, such as for dopant element B, the first concentration decreases with increasing height of the active layer in the gradient doping region 141B. In this embodiment, the first concentration ranges from 5E17 cm⁻¹. -3 Up to 2E18 cm -3 The final concentration range of the first concentration is 1E17 cm⁻¹. -3 Up to 5E17 cm -3 In some embodiments, the ratio of the initial concentration of the first concentration to the final concentration of the first concentration (i.e., the second concentration) is greater than 1.5.

[0061] In some embodiments, the dopant element further dops the second semiconductor layer at a second concentration. In some embodiments, the doping of the dopant element is stopped after the active layer growth is completed.

[0062] See Figure 5C The active layer doping method 500C includes steps 502C to 506C.

[0063] Step 502C: Doping one or more doping elements at a first concentration within the first uniform doping region. (Combined) Figure 2C In some embodiments, the active layer 140 includes a first uniform doped region 141C, a gradient doped region 142C, and a second uniform doped region 142C. In the first uniform doped region 141C, the doping concentration of the doping element (e.g., doping element A or doping element B) is a first concentration, and the variation amplitude of the first concentration in the first uniform doped region 141C does not exceed 20%, that is, it is relatively fixed.

[0064] Step 504C: Doping the one or more doping elements at a second concentration in the gradient doping region 142C. Within the gradient doping region 142C, the doping concentration of the doping element (e.g., doping element A or doping element B) is a second concentration, which varies with the height of the active layer 140, i.e., varies with the growth height of the active layer 140.

[0065] Step 506C: Doping the one or more doping elements in the second uniform doping region with a third concentration. In the second uniform doping region 143C, the doping concentration of the doping element (e.g., doping element A or doping element B) is the third concentration, and the variation range of this third concentration in the second uniform doping region 143C does not exceed 20%, i.e., it is relatively fixed.

[0066] According to method 500C, a first uniformly doped region 141C is located near the first semiconductor layer 130, a second uniformly doped region 143C is located near the second semiconductor layer 150, and a gradient doped region 142C is located between the first uniformly doped region 141C and the second uniformly doped region 143C. The initial concentration of the second concentration is the concentration of the first concentration, that is, the dopant element is doped at the first concentration in the first region 141C with the active layer. When doping reaches point P, the concentration increases or decreases with the growth height of the active layer 140, starting from the first concentration. The final concentration of the second concentration is the third concentration, that is, the dopant element is doped at the second concentration in the gradient doped region 142C of the active layer. The doping concentration increases or decreases with the height of the active layer. When doping reaches point Q, the concentration at point Q is used as the third concentration in the second uniformly doped region 143C. The variation amplitude of the third concentration in the second uniformly doped region 143C does not exceed 20%, that is, it is relatively fixed. In this embodiment, the region from the starting point of the active layer 140 to point P is the first uniform doping region, the region growing from point P to point Q is the gradient doping region, and the region continuing to grow from point Q to the end position of the active layer 140 is the second uniform doping region.

[0067] In some embodiments, such as for dopant element A, the second concentration increases with increasing height of the active layer in the gradient doping region 142C. In this embodiment, the first concentration ranges from 2E to 16 cm⁻¹. -3 Up to 5E17 cm -3 The third concentration range is 5E 17 cm⁻¹ -3 Up to 2E 18 cm -3 In some embodiments, the ratio of the third concentration to the first concentration is greater than 1.5.

[0068] In some embodiments, such as for dopant element B, the second concentration decreases with increasing height of the active layer in the gradient doping region 142C. In this embodiment, the first concentration ranges from 5E17 cm⁻¹. -3 Up to 2E18 cm -3 The third concentration range is 1E17 cm⁻¹ -3 Up to 5E17 cm -3 In some embodiments, the ratio of the first concentration to the third concentration is greater than 1.5.

[0069] In some embodiments, the dopant element further dops the second semiconductor layer at a third concentration. In some embodiments, doping is stopped after the active layer growth is complete.

[0070] By combining uniform doping and gradient doping to dope the active layer, the internal quantum efficiency and light extraction efficiency of the active layer can be improved, thereby improving the external quantum efficiency and brightness uniformity of the micro LED display chip.

[0071] In some embodiments, one or more doping elements are doped into the active layer by spaced doping. Figure 6 This is a flowchart illustrating a method for spacing doped active layers according to some embodiments of this application. See also... Figure 5A The active layer doping method 600 includes steps 602 and 604.

[0072] Step 602: Doping the quantum barrier layer with one or more doping elements at a fifth concentration. In some embodiments, the doping elements are doped at the fifth concentration at the location where the quantum barrier layer begins to grow until near the location where the quantum barrier layer growth ends.

[0073] Step 604 involves doping the quantum well layer with one or more dopant elements at a fourth concentration. For example, doping with a fourth concentration can be performed near the location where the quantum well layer W begins to grow. Steps 602 and 604 are repeated during the alternating growth of the quantum well layer and the quantum barrier layer.

[0074] Combination Figure 3A and Figure 3B In some embodiments, the fifth concentration in the quantum barrier layer is greater than the fourth concentration in the quantum well layer. In some embodiments, the fifth concentration in the quantum barrier layer is less than the fourth concentration in the quantum well layer.

[0075] In some embodiments, step 602 further includes doping the quantum barrier layer with one or more doping elements at a fifth concentration from the starting position of the quantum barrier layer growth to a first position, and then doping the one or more doping elements at a fourth concentration from the first position to the end of the quantum barrier layer growth. Figure 3BTaking quantum barrier layer 1402 as an example, quantum barrier layer 1402 grows from position a to position b, where growth ends and the next quantum well layer W begins. Starting from position a, a dopant element is doped into quantum barrier layer 1402 at a fifth concentration of C2 until quantum barrier layer 1402 grows to position c. From position c, the dopant element is then doped into quantum barrier layer 1402 at a fourth concentration of C1, and the fourth concentration of C1 is continued to be used to dope quantum well layer W. The region where quantum barrier layer 1402 grows from position c to position b is the buffer region. In some embodiments, the thickness of the buffer region is one-third to four-fifths of the thickness of the corresponding quantum barrier layer, that is, the distance from point c to point b is one-third to four-fifths of the distance from point a to point b.

[0076] In some embodiments, step 604 further includes doping the quantum well layer with one or more doping elements at a fourth concentration from the starting position of the quantum well layer growth to a second position, and then doping the one or more doping elements at a fifth concentration from the second position to the end of the quantum well layer growth. Figure 3A Taking quantum well layer 1401 as an example, quantum well layer 1401 grows from position a to position b, ending at which point the growth of the next quantum barrier layer B begins. Starting from position a, a dopant element is doped into quantum well layer 1401 at a fourth concentration C1 until quantum well layer 1401 grows to position c. From position c, the dopant element is then doped into quantum well layer 1401 at a fifth concentration C2, and this fifth concentration C2 is continued for quantum barrier layer B. The region where quantum well layer 1401 grows from position c to position b is the buffer region. In some embodiments, the thickness of the buffer region is one-third to four-fifths of the thickness of its corresponding quantum well layer, that is, the distance from point c to point b is one-third to four-fifths of the distance from point a to point b.

[0077] The doping method of the active layer provided by this application enables the epitaxial layer of the micro LED chip to control the stress of the epitaxial layer and the wavelength of light emission, thereby improving the internal quantum efficiency and light extraction efficiency of the active layer, and thus improving the external quantum efficiency and brightness uniformity of the micro LED chip.

[0078] It should be noted that relational terms in this document, such as “first” and “second”, are used only to distinguish an entity or operation from another entity or operation, without requiring or implying any actual relationship or order between these entities or operations. Furthermore, the words “including,” “having,” and “containing,” as well as other similar forms, are intended to be equivalent in meaning and are open-ended; one or more items following any of these words do not imply an exhaustive list of such items or that the list is limited to only one or more items.

[0079] As used herein, unless expressly stated otherwise, the term "or" covers all possible combinations unless impractical. For example, if a component is stated to include A or B, then unless expressly stated otherwise or impractical, the component may include A, or B, or A and B. As a second example, if a component is stated to include A, B, or C, then unless expressly stated otherwise or impractical, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0080] In the foregoing description, numerous specific details have been described, which may vary depending on the implementation. Certain modifications and alterations may be made to the described embodiments. Other embodiments will be apparent to those skilled in the art in light of the specification and practice of this application disclosed herein. The specification and examples are intended to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims. The sequence of steps shown in the accompanying drawings is also intended for illustrative purposes only and is not intended to limit one to any particular order of steps. Therefore, those skilled in the art will understand that these steps may be performed in different orders while achieving the same method.

[0081] Exemplary embodiments have been disclosed in the accompanying drawings and description. However, many variations and modifications can be made to these embodiments. Therefore, although specific terminology has been used, it is used in a general and descriptive sense only and not for limiting purposes.

Claims

1. A micro LED chip, comprising an epitaxial layer, wherein the epitaxial layer comprises, from bottom to top, a first semiconductor layer, an active layer, and a second semiconductor layer, characterized in that, The active layer is doped with one or more doping elements, each of which is doped in the active layer in a combination of continuous uniform doping and continuous gradient doping. The regions of continuous uniform doping and continuous gradient doping constitute the entire region of the active layer. In the regions of continuous uniform doping, the doping concentration variation of the doping element does not exceed 20%.

2. The micro LED chip according to claim 1, characterized in that, The active layer includes a first region and a second region. The first region is a region of continuous uniform doping, and the second region is a region of continuous gradient doping. The first region is close to the first semiconductor layer, and the second region is close to the second semiconductor layer. The doping concentration of the doping element in the first region is a first concentration, and the doping concentration of the doping element in the second region is a second concentration. The second concentration varies with the height of the active layer, and the initial concentration of the second concentration is the first concentration.

3. The micro LED chip according to claim 2, characterized in that, The second concentration increases with the increase of the height of the active layer.

4. The micro LED chip according to claim 2, characterized in that, The second concentration decreases as the height of the active layer increases.

5. The micro LED chip according to claim 1, characterized in that, The active layer includes a first region and a second region. The first region is a region of continuous uniform doping, and the second region is a region of continuous gradient doping. The first region is close to the second semiconductor layer, and the second region is close to the first semiconductor layer. The doping concentration of the dopant element in the first region is a first concentration, and the doping concentration of the dopant element in the second region is a second concentration. The second concentration varies with the height of the active layer, and the final concentration of the second concentration is the first concentration.

6. The micro LED chip according to claim 5, characterized in that, The second concentration increases with the increase of the height of the active layer.

7. The micro LED chip according to claim 5, characterized in that, The second concentration decreases as the height of the active layer increases.

8. The micro LED chip according to claim 1, characterized in that, The active layer includes a first region, a second region, and a third region. The first region and the third region are each of the continuously uniformly doped regions, and the second region is the continuously gradient doped region. The second region is located between the first region and the third region.

9. The micro LED chip according to claim 1, characterized in that, The active layer includes multiple quantum well layers and multiple quantum barrier layers arranged at intervals. The doping concentration of the dopant element in the quantum well layer is a fourth concentration, and the doping concentration of the dopant element in the quantum barrier layer is a fifth concentration. The fourth concentration and the fifth concentration are different.

10. The micro LED chip according to claim 9, characterized in that, The fourth concentration is greater than the fifth concentration, and the ratio of the fourth concentration to the fifth concentration is greater than 1.

5.

11. The micro LED chip according to claim 9, characterized in that, The fourth concentration is less than the fifth concentration, and the ratio of the fifth concentration to the fourth concentration is greater than 1.

5.

12. The micro LED chip according to claim 9, characterized in that, The quantum well layer or the quantum barrier layer includes a buffer region, the doping concentration of the dopant element in the buffer region of the quantum well layer is the fifth concentration, and the doping concentration of the dopant element in the buffer region of the quantum barrier layer is the fourth concentration.

13. The micro LED chip according to claim 12, characterized in that, The ratio of the thickness of the buffer region to the thickness of the quantum well layer or the quantum barrier layer ranges from one-third to four-fifths.

14. The micro LED chip according to claim 12, characterized in that, The ratio of the thickness of the buffer region to the thickness of the quantum well layer or the quantum barrier layer ranges from two-thirds to four-fifths.

15. The micro LED chip according to claim 1, characterized in that, The doping element is one or more of Mg, As, Sb, Fe, Zn, Si, Te, and Bi.

16. The micro LED chip according to claim 1, characterized in that, The concentration of the dopant element is greater than or equal to 2E16 cm⁻¹ -3 And less than or equal to 2E18 cm -3 .

17. A method for preparing an epitaxial layer in a micro LED chip according to claim 1, comprising: Provide substrate; A buffer layer is grown on the substrate; A first semiconductor layer is grown on the buffer layer; An active layer is grown on the first semiconductor layer; as well as Growing a second semiconductor layer on the active layer; characterized in that growing the active layer on the first semiconductor layer comprises: The active layer is doped with one or more doping elements by a combination of continuous uniform doping and continuous gradient doping.

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