Patent Publication Number: US-2019198708-A1

Title: Light emitting diode epitaxial wafer and method for manufacturing the same

Description:
FIELD 
     The subject matter relates to a light emitting device, and particularly relates to a light emitting diode (LED) epitaxial wafer and a method for manufacturing the same. 
     BACKGROUND 
     During the manufacturing of LEDs, InGaN/GaN films are grown on the C-plane of a sapphire substrate. However, Quantum Confined Stark Effect (QCSE) may be generated in the LEDs, which reduces the internal quantum efficiency and the luminosity intensity. Improvements in the art are preferred. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present disclosure will now be described, by way of example only, with reference to the attached figures, wherein: 
         FIG. 1  is a cross-sectional view of an exemplary embodiment of an LED epitaxial wafer, in accordance with the present disclosure. 
         FIG. 2  is a diagram showing a content of aluminum linearly increasing in a quantum well region of the LED epitaxial wafer of  FIG. 1 , in accordance with a first exemplary embodiment of the present disclosure. 
         FIG. 3  is a diagram showing a content of indium linearly increasing in a quantum well region of the LED epitaxial wafer of  FIG. 1 , in accordance with a second exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments described herein. However, it will be understood by those of ordinary skill in the art that the exemplary embodiments described herein can be practiced without these specific details. 
     In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the exemplary embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
     Definitions that apply throughout this disclosure will now be presented. 
     The term “substantially” is defined to be essentially conforming to the particular dimension, shape, or other feature that the term modifies, such that the component need not be exact. For example, “substantially rectangular” means that the object resembles a rectangle, but can have one or more deviations from a true rectangle. 
     The term “comprising,” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, assembly, series, and the like. 
     Referring to  FIG. 1 , the LED epitaxial wafer  1  comprises a substrate  100  and an epitaxial structure  200 . The epitaxial structure  200  is grown on the substrate  100 . 
     Referring to  FIG. 2 , the substrate  100  is made of sapphire that has a high mechanical strength and is easy to be processed. The epitaxial structure  200  is formed on the C-plane of the substrate  100 . 
     The epitaxial structure  200  comprises a buffer layer  20 , an N-type semiconductor layer  30 , a light-emitting active layer  40 , and a P-type semiconductor layer  50 . The buffer layer  20 , the N-type semiconductor layer  30 , the light-emitting active layer  40 , and the P-type semiconductor layer  50  are formed on the c-plane of the substrate  100  in that order. The buffer layer  20  is made of pure gallium nitride (GaN), which is mainly used to reduce lattice defects of the N-type semiconductor layer  30 . An ohmic contact layer (not shown) may be disposed on the P-type semiconductor layer  50 , in order to improve current transmission efficiency. 
     The P-type semiconductor layer  50  provides electron holes, and is mainly made of P-type gallium nitride (GaN). The N-type semiconductor layer  30  provides electrons, and is mainly made of doped gallium nitride (GaN), such as AlGaN. The light-emitting active layer  40  is made of gallium nitride-based material, such as InGaN, GaN, and generates light. The light-emitting active layer  40  further limits electrons and holes to increase the luminous intensity. 
     Referring to  FIG. 2  and  FIG. 3 , the light-emitting active layer  40  comprises at least one quantum well structure  42 . Each quantum well structure  42  comprises a quantum well region  422 , a gradient region  424 , a high-content aluminum region  426 , and a blocking region  428 . The blocking region  428  covers and connects with the high aluminum region  426 . The P-type semiconductor layer  50  covers and connects with the blocking region  428 . In the exemplary embodiment, the number of quantum well structures  42  is between 5 and 10. 
     Example 1 
     Referring to  FIG. 2 , the quantum well region  422  covers and connects with the N-type semiconductor layer  30 . The gradient region  424  is located between the quantum well region  422  and the high-content aluminum region  426 , and connects the quantum well region  422  and the high-content aluminum region  426 . 
     The quantum well region  422  is used to limit the electrons and electron holes to achieve effective recombination. The quantum well region  422  is made of indium-doped gallium nitride (GaN) that has a chemical formula of In x Ga 1-x N, 0&lt;x&lt;1. The thickness of the quantum well region  422  ranges from 1 to 3 nanometers. 
     The gradient region  424  is used to reduce the quantum confinement Stark effect in the light-emitting diode. The gradient region  424  is made of aluminum-doped gallium nitride (GaN) that has a chemical formula of Al y Ga 1-y N, 0&lt;y≤1. The content of aluminum increases linearly from a side close to the N-type semiconductor layer  30  to the other side away from the N-type semiconductor layer  30 . The thickness of the gradient region  424  ranges from 1 to 2 nanometers. 
     The high-content aluminum region  426  is used to block the diffusion of indium from the quantum well region  422  to the blocking region  428 . The high-content aluminum region  426  is made of aluminum-doped gallium nitride (GaN) that has chemical formula of Al z Ga 1-z N and 0.7≤z&lt;1. The thickness of the high aluminum region  426  ranges from 1 to 2 nanometers. 
     The blocking region  428  is an electron blocking layer, and is made of indium-doped gallium nitride (GaN) that has a chemical formula of In t Ga 1-t N, 0≤t&lt;1. The blocking region  428  has a thickness of 10 to 12 nanometers. 
     A method for manufacturing the LED epitaxial wafer  1  of the example 1 comprises the following steps: 
     Step 1: a substrate  100  is provided. 
     Step 2: a buffer layer  20  is grown on the C-plane of the substrate  100 . The buffer layer  20  can be formed by one of an organic metal chemical vapor deposition method, a radio frequency magnetron sputtering method, a chemical vapor deposition method, a physical vapor deposition method, an atomic layer deposition method, and a molecular beam deposition method. 
     Step 3: an N-type semiconductor layer  30  is grown on the buffer layer  20 . The growth N-type semiconductor layer  30  may also be formed by one of organic metal chemical vapor deposition, radio frequency magnetron sputtering, chemical vapor deposition, physical vapor deposition, atomic layer deposition, and molecular beam deposition method. 
     Step 4: a quantum well region  422  is grown on the N-type semiconductor layer  30 . The quantum well region  422  is made of indium-doped gallium nitride (GaN) that has a chemical formula of In x Ga 1-x N, 0&lt;x&lt;1. The thickness of the quantum well region  422  ranges from 1 to 3 nanometers. 
     Step 5: a gradient region  424  is grown on the quantum well region  422 . The aluminum gradient region is made of aluminum-doped gallium nitride (GaN) that has a chemical formula of Al y Ga 1-y N, 0&lt;y≤1. The content of aluminum increases linearly from a side close to the N-type semiconductor layer  30  to the other side away from the N-type semiconductor layer  30 . The thickness of the aluminum gradient region ranges from 1 to 2 nanometers. The epitaxial temperature of the gradient region  424  is gradual and ranges from 50 to 100 degrees Celsius. 
     Step 6: a high aluminum region  426  is grown on the gradient region  422 . The high-content aluminum region is made of aluminum-doped gallium nitride (GaN) that has a chemical formula of Al z Ga 1-z N, and 0.7≤z&lt;1. The thickness of the high aluminum region  426  ranges from 1 to 2 nanometers. The epitaxial temperature of the high-content aluminum region  426  is 50-100 degrees Celsius higher than that of the quantum well region  422 . 
     Step 7: a blocking region  428  is grown on the high-content aluminum region  426 . The blocking region  428  is made of indium-doped gallium nitride (GaN) that has a chemical formula of In t Ga 1-t N, and 0≤t&lt;1. The blocking region  428  has a thickness of 10 to 12 nanometers. 
     Step 8: a P-type semiconductor layer  50  is grown on the blocking region  4   
     Thus, the LED epitaxial wafer  1  is formed. 
     Example 2 
     Referring to  FIG. 3 , the gradient region  424  covers and connects to the N-type semiconductor layer  30 . The quantum well region  422  is located between the gradient region  424  and the high-content aluminum region  426 , and connects the gradient region  424  and the high-content aluminum region  426 . 
     The gradient region  424  is used to reduce the quantum confinement Stark effect in the light-emitting diode. The gradient region  424  is made of an indium-doped gallium nitride (GaN) that has chemical formula of In x Ga 1-x N, 0≤x≤1. The content of indium decreases linearly from a side close to the N-type semiconductor layer  30  to the other side away from the N-type semiconductor layer  30 . The thickness of the gradient region  424  ranges from 1 to 2 nanometers. 
     The quantum well region  422  is used to limit the electrons and electron holes to achieve effective recombination. The quantum well region  422  is made of indium-doped gallium nitride (GaN) that has a chemical formula of In y Ga 1-y N, 0&lt;y≤1. The thickness of the quantum well region  422  ranges from 1 to 3 nanometers. 
     The high-content aluminum region  426  is used to block the diffusion of indium from the quantum well region  422  to the blocking region  428 . The high-content aluminum region is made of aluminum-doped gallium nitride (GaN) that has a chemical formula of Al z Ga 1-z N and 0.7≤z&lt;1. The thickness of the high aluminum region  426  ranges from 1 to 2 nanometers. 
     The blocking region  428  is an electron blocking layer, and is made of indium-doped gallium nitride (GaN) that has a chemical formula of In t Ga 1-t N, 0≤t&lt;1. The blocking region  428  has a thickness of 10 to 12 nanometers. 
     A method for manufacturing the LED epitaxial wafer  1  of the above example 2 comprises the following steps: 
     Step 1: a substrate  100  is provided. 
     Step 2: the buffer layer  20  is grown on the C-plane of the substrate  100 . The buffer layer  20  can be formed by any one of an organic metal chemical vapor deposition method, a radio frequency magnetron sputtering method, a chemical vapor deposition method, a physical vapor deposition method, an atomic layer deposition method, and a molecular beam deposition method. 
     Step 3: an N-type semiconductor layer  30  is grown on the buffer layer  20 . The growth N-type semiconductor layer  30  may also be formed by one of organic metal chemical vapor deposition, radio frequency magnetron sputtering, chemical vapor deposition, physical vapor deposition, atomic layer deposition, and molecular beam deposition method. 
     Step 4: a gradient region  424  is grown on the N-type semiconductor layer  30 . The gradient region  424  is made of an indium-doped gallium nitride (GaN) that has a chemical formula of In x Ga 1-x N, 0≤x≤1. The content of indium decreases linearly from a side close to the N-type semiconductor layer  30  to the other side away from the N-type semiconductor layer  30 . The thickness of the indium gradient region ranges from 1 to 2 nanometers. 
     Step 5: a quantum well region  422  is grown on the indium gradient region. The quantum well region  422  is made of indium-doped gallium nitride (GaN) that has a chemical formula of In y Ga 1-y N, 0&lt;y≤1. The thickness of the quantum well region  422  ranges from 1 to 3 nanometers. 
     Step 6: a high-content aluminum region  426  is grown on the quantum well region  422 . The high-content aluminum region  426  is made of aluminum-doped gallium nitride (GaN) that has a chemical formula of Al z Ga 1-z N, and 0.7≤z&lt;1. The thickness of the high aluminum region  426  ranges from 1 to 2 nanometers. The epitaxial temperature of the high-content aluminum region  426  is 50-100 degrees Celsius higher than that of the quantum well region  422 . 
     Step 7: a blocking region  428  is grown on the high-content aluminum region  426 . The blocking region  428  is made of an indium-doped gallium nitride (GaN) material having a chemical formula of In t Ga 1-t N and 0≤t&lt;1. The blocking region  428  has a thickness of 10 to 12 nanometers. 
     Step 8: a P-type semiconductor layer  50  is grown on the blocking region  428 . Thus, the LED epitaxial wafer  1  is formed. 
     With the above configuration, the gradient region  424  is grown on the C-plane of the sapphire substrate  100 . The content of indium or of aluminum of the gradient region  424  changes linearly from the side close to the N-type semiconductor layer  30  to the side away from the N-type semiconductor layer  30 , so as to reduce the quantum confinement Stark effect. In addition, the quantum well structure  42  has a high-content aluminum region  426  that can reduce the phenomenon of indium diffusion in the blocking region  428  and the quantum well region  422 , thereby enhancing the epitaxial quality of the light-emitting active layer  40 . 
     The embodiments shown and described above are only examples. Many other details are found in the art. Therefore, many such details are neither shown nor described. Even though numerous characteristics and advantages of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, especially in matters of shape, size, and arrangement of the parts within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims. It will therefore be appreciated that the embodiments described above may be modified within the scope of the claims.