Patent Publication Number: US-2023163241-A1

Title: Method for growing electron-blocking layer, epitaxial layer, and light-emitting diode chip

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2021/130007, filed on Nov. 11, 2021, the entire disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to the field of semiconductor technology, and in particular to a method for growing an electron-blocking layer, an epitaxial layer, and a light-emitting diode (LED) chip. 
     BACKGROUND 
     Group III-nitride based devices such as Gallium Nitride (GaN) based LED chips, have attracted much attention due to their high reliability, high cost performance, and high efficiency, and are widely used in various industries. With development of a production process of GaN-based LED chips, higher requirements are put forward in the industry on the luminescent efficiency of GaN-based LED chips, and how to improve the luminescent efficiency of LED chips is a problem to be solved urgently at present. 
     SUMMARY 
     An epitaxial layer is provided in the present disclose. The epitaxial layer includes an N-type semiconductor layer, an active layer, a p-type semiconductor layer, and an electron-blocking layer. The electron-blocking layer is disposed between the active layer and the P-type semiconductor layer, and the N-type semiconductor layer is disposed on one side of the active layer away from the electron-blocking layer. The electron-blocking layer includes a proximal aluminum barrier layer close to the active layer, a distal aluminum barrier layer close to the P-type semiconductor layer, and an indium well layer disposed between the proximal aluminum barrier layer and the distal aluminum barrier layer, where a content of aluminum component in the distal aluminum barrier layer is lower than a content of aluminum component in the proximal aluminum barrier layer. 
     Based on the same inventive concept, an LED chip is further provided in the present disclosure. The LED chip includes an N-type semiconductor layer, an active layer, a P-type semiconductor layer, an electron-blocking layer, an N-electrode electrically coupled with the N-type semiconductor layer, and a p-electrode electrically coupled with the p-type semiconductor layer. The electron-blocking layer is disposed between the active layer and the P-type semiconductor layer, and the N-type semiconductor layer is disposed on one side of the active layer away from the electron-blocking layer. The electron-blocking layer includes a proximal aluminum barrier layer close to the active layer, a distal aluminum barrier layer close to the P-type semiconductor layer, and an indium well layer disposed between the proximal aluminum barrier layer and the distal aluminum barrier layer, where a content of aluminum component in the distal aluminum barrier layer is lower than a content of aluminum component in the proximal aluminum barrier layer. 
     Based on the same inventive concept, a method for growing an electron-blocking layer is further provided in the present disclosure. The method includes the following. Grow a proximal aluminum barrier layer on a surface of an active layer away from an N-type semiconductor layer. Grow an indium well layer on the proximal aluminum barrier layer. Grow a distal aluminum barrier layer on the indium well layer, a content of aluminum component in the distal aluminum barrier layer being lower than a content of aluminum component in the proximal aluminum barrier layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a structural schematic diagram of an epitaxial layer provided in an implementation of the present disclosure. 
         FIG.  2    is a schematic flowchart illustrating a method for growing an electron-blocking layer provided in an implementation of the present disclosure. 
         FIG.  3    is a schematic diagram illustrating a process for growing an electron-blocking layer provided in an implementation of the present disclosure. 
         FIG.  4    is a schematic flowchart illustrating growing a proximal aluminum barrier layer provided in an implementation of the present disclosure. 
         FIG.  5    is a schematic diagram illustrating a process for growing a proximal aluminum barrier layer provided in an implementation of the present disclosure. 
         FIG.  6    is a schematic diagram illustrating a variation of a content of aluminum component during growth of a proximal aluminum barrier layer provided in an implementation of the present disclosure. 
         FIG.  7    is a schematic diagram illustrating a variation of a content of aluminum component during growth of a proximal aluminum barrier layer provided in another implementation of the present disclosure. 
         FIG.  8    is a schematic flowchart illustrating growing an indium well layer provided in an implementation of the present disclosure. 
         FIG.  9    is a schematic diagram illustrating a process for growing an indium well layer provided in an implementation of the present disclosure. 
         FIG.  10    is a schematic diagram illustrating a variation of a content of indium component during growth of an indium well layer provided in an implementation of the present disclosure. 
         FIG.  11    is a schematic flowchart illustrating growing a distal aluminum barrier layer provided in an implementation of the present disclosure. 
         FIG.  12    is a schematic diagram illustrating a process for growing a distal aluminum barrier layer provided in an implementation of the present disclosure. 
         FIG.  13    is a schematic diagram illustrating a variation of a content of aluminum component during growth of a distal aluminum barrier layer provided in an implementation of the present disclosure. 
         FIG.  14    is a schematic structural diagram of an LED chip provided in an implementation of the present disclosure. 
         FIG.  15    is a schematic structural diagram of an epitaxial layer provided in another implementation of the present disclosure. 
         FIG.  16    is a schematic flowchart illustrating growing an epitaxial layer provided in another implementation of the present disclosure. 
         FIG.  17    is a schematic diagram illustrating a process for growing an epitaxial layer provided in another implementation of the present disclosure. 
         FIG.  18    is a schematic structural diagram of an electron-blocking layer provided in another implementation of the present disclosure. 
         FIG.  19    is a schematic diagram illustrating a variation of a content of aluminum component and nitrogen component during growth of an electron-blocking layer provided in another implementation of the present disclosure. 
     
    
    
     DESCRIPTION OF REFERENCE SIGNS 
       10 —epitaxial layer;  11 —N-type semiconductor layer;  12 —active layer;  13 —P-type semiconductor layer;  14 —electron-blocking layer;  141 —proximal aluminum barrier layer;  1411 —first sub-layer;  1412 —second sub-layer;  1413 —third sub-layer;  142 —indium well layer;  1421 —fourth sub-layer;  1422 —fifth sub-layer;  143 —distal aluminum barrier layer;  1431 —sixth sub-layer;  1432 —seventh sub-layer;  8 —LED chip;  81 —N-electrode;  83 —P-electrode;  90 —epitaxial layer;  91 —substrate;  92 —buffer layer;  93 —GaN intrinsic layer;  94 —N-type GaN layer;  95 —N-type retardation layer;  96 —active layer;  97 —electron-blocking layer;  971 —proximal AlGaN layer;  9711 —first sub-layer;  9712 —second sub-layer;  9713 —third sub-layer;  972 —InGaN layer;  9721 —fourth sub-layer;  9722 —fifth sub-layer;  973 —distal AlGaN layer;  9731 —sixth sub-layer;  9732 —seventh sub-layer; and  98 —P-type GaN layer. 
     DETAILED DESCRIPTION 
     In order for those skilled in the art to better understand technical solutions of the disclosure, technical solutions of implementations will be described clearly and completely with reference to accompanying drawings in the implementations. Apparently, implementations described hereinafter are merely some implementations, rather than all implementations of the disclosure. All other implementations obtained by those of ordinary skill in the art based on the implementations without creative efforts shall fall within the protection scope of the disclosure. 
     In order to facilitate understanding of the present disclosure, the present disclosure will be described completely hereinafter with reference to accompanying drawings. Preferred implementations of the present disclosure are illustrated in the accompanying drawings, however, the present disclosure may be implemented in many different forms and is not limited to implementations described herein. Rather, implementations are provided to make the present disclosure thorough and complete. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the field to which the disclosure belongs. The terms used herein in the description of the present disclosure is for the purpose of describing specific implementations only and is not intended to limit the present disclosure. 
     An LED device is a semiconductor electronic device for converting electrical energy into light energy. When a current flows, electrons and holes recombine in an active layer to emit light. As a highly efficient, environmentally friendly, and green novel solid state light source, an LED has advantages of low voltage, low power consumption, small volume, light weight, long service life, high reliability, etc., and is rapidly and widely applied, especially in the field of lighting and display. 
     How to improve the luminescent efficiency of an LED chip has always been a research hotspot in the industry. On this basis, a solution capable of solving the described technical problem is to be provided in the present disclosure and will be described in detail in subsequent implementations. 
     An alternative implementation is provided in the present disclosure. 
     An epitaxial layer is first provided in the present disclosure and reference can be made to  FIG.  1    which is a schematic structural diagram of an epitaxial layer. The epitaxial layer  10  includes an N-type semiconductor layer  11 , an active layer  12 , and a P-type semiconductor layer  13 , and the active layer  12  is disposed between the N-type semiconductor layer  11  and the P-type semiconductor layer  13 . The epitaxial layer  10  further includes an electron-blocking layer (EBL)  14 , the electron-blocking layer  14  is disposed between the active layer  12  and the P-type semiconductor layer  13 , and the electron-blocking layer  14  can block electrons escaping from the active layer  12  from entering the P-type semiconductor layer  13 . It can be understood that the epitaxial layer  10  can further include one or more other layered structures, such as at least one of a buffer layer, an intrinsic layer, an ohmic contact layer, etc. 
     In this implementation, from one side of the electron-blocking layer  14  close to the active layer  12  to one side of the electron-blocking layer  14  close to the P-type semiconductor layer  13 , the electron-blocking layer  14  includes a proximal aluminum barrier layer  141 , an indium well layer  142 , and a distal aluminum barrier layer  143  in sequence. Terms “proximal” and “distal” in expressions “proximal aluminum barrier layer” and “distal aluminum barrier layer” are defined according to distances of two layered structures relative to the active layer  12 . The proximal aluminum barrier layer  141  is relatively close to the active layer  12 , and the distal aluminum barrier layer  143  is relatively far away from the active layer  12 . In this implementation, the indium well layer  142  serves as a channel layer, and forms a hole-injection pumping structure together with the proximal aluminum barrier layer  141  and the distal aluminum barrier layer  143 , which can increase injection efficiency of holes in the P-type semiconductor layer  13  into the active layer  12 , thereby increasing a probability of recombination of electrons and holes in the active layer  12 . 
     Since a content of aluminum component in the distal aluminum barrier layer  143  is lower than a content of aluminum component in the proximal aluminum barrier layer  141 , a potential barrier of the distal aluminum barrier layer  143  is lower than a potential barrier of the proximal aluminum barrier layer  141 , which helps to reduce a forward voltage of an LED chip. In some implementations, the content of the aluminum component in the distal aluminum barrier layer  143  is 45% to 75% of the content of the aluminum component in the proximal aluminum barrier layer  141 , such as 50% to 70%. In some examples, the content of the aluminum component in the distal aluminum barrier layer  143  is any one of 45%, 50%, 55%, 60%, or 75% of the content of the aluminum component in the proximal aluminum barrier layer  141 . It can be understood by those skilled in the art a percentage of contents of the aluminum component in the distal aluminum barrier layer  143  and the proximal aluminum barrier layer  141  are not limited herein. 
     In some implementations, the proximal aluminum barrier layer  141  and the distal aluminum barrier layer  143  each contain Aluminum Gallium Nitride (AlGaN). In some implementations, the indium barrier layer  142  contains Indium Gallium Nitride (InGaN). It can be understood that the electron-blocking layer  14  may be a p-type doped layered structure, and the electron-blocking layer  14  may contain a p-type doped element, which may include but is not limited to Magnesium (Mg), Zinc (Zn), and the like. 
     A method for growing an electron-blocking layer  14  is further provided in the present disclosure and reference can be made to  FIG.  2    and  FIG.  3   . 
     S 202 , grow a proximal aluminum barrier layer on a surface of an active layer away from an N-type semiconductor layer. 
     It can be understood that, the electron-blocking layer  14  is disposed between the active layer  12  and the P-type semiconductor layer  13 , and in the process of growing the epitaxial layer  10 , the electron-blocking layer  14  generally grows from the N-type semiconductor layer  11  to the P-type semiconductor layer  13 , therefore the electron-blocking layer  14  should be epitaxially grown on the active layer  12  after the growth of the active layer  12 . It can be understood that, an N-type semiconductor layer  11  is further grown under the active layer  12 , and reference can be made to part (a) of  FIG.  3   , the proximal aluminum barrier layer  141  is grown on one side of the active layer  12  away from the N-type semiconductor layer  11 , as illustrated in part (b) pf  FIG.  3   . 
     S 204 , grow an indium well layer on the proximal aluminum barrier layer. 
     After the proximal aluminum barrier layer  141  is grown, the indium well layer  142  is epitaxially grown on the proximal aluminum barrier layer  141 , as illustrated in part (c) of  FIG.  3   . 
     S 206 , grow a distal aluminum barrier layer on the indium well layer, a content of aluminum component in the distal aluminum barrier layer being lower than a content of aluminum component in the proximal aluminum barrier layer. 
     After the indium well layer  142  is grown, the distal aluminum barrier layer  143  is grown on the indium well layer  142 , as illustrated in part (d) of  FIG.  3   , In this implementation, a content of aluminum source introduced into an reaction chamber when the distal aluminum barrier layer  143  is grown is lower than a content of aluminum source introduced into the reaction chamber when the proximal aluminum barrier layer  141  is grown, In this way, it can be ensured that the content of the aluminum component in the grown distal aluminum barrier layer  143  is lower than the content of the aluminum component in the proximal aluminum barrier layer  141 . In this way, it can be ensured that the potential barrier of the distal aluminum barrier layer  143  is lower than the potential barrier of the proximal aluminum barrier layer  141 . 
     In some implementations, when the electron-blocking layer  14  is grown, growth with component varying in a gradient manner is adopted in at least one stage, and thus at least one of the content of the aluminum component in the proximal aluminum barrier layer  141 , the content of the aluminum component in the distal aluminum barrier layer  143 , or the content of the indium component in the indium well layer  142  varies in a gradient manner. For example, in the electron-blocking layer  14 , only the content of the aluminum component in the proximal aluminum barrier layer  141  varies in a gradient manner, only the content of the aluminum component in the distal aluminum barrier layer  143  varies in a gradient manner, or only the content of the indium component in the indium well layer  142  varies in a gradient manner. In other implementations, the content of the aluminum component in the proximal aluminum barrier layer  141  and the content of the indium component in the indium well layer  142  vary in a gradient manner, or the content of the aluminum component in the proximal aluminum barrier layer  141  and the content of the aluminum component in the distal aluminum barrier layer  143  vary in a gradient manner, or the content of the aluminum component in the distal aluminum barrier layer  143  and the content of the indium component in the indium well layer  142  vary in a gradient manner. In some implementations, in the electron-blocking layer  14 , the content of the aluminum component in the proximal aluminum barrier layer  141 , the content of the aluminum component in the distal aluminum barrier layer  143  and the content of the indium component in the indium well layer  142  vary in a gradient manner. 
     It can be understood that, the gradient manner includes two types: a linear gradient and a stepwise gradient. In some implementations, a layered structure in the electron-blocking layer  14  where a content of component varies in a gradient manner may grow in a linear gradient manner, and may also grow in a stepwise gradient manner. In other implementations, part of layer structures in the electron-blocking layer  14  where a content of component varies in a gradient manner grow in a linear gradient manner, and the other parts of layer structures grow in a stepwise gradient manner. 
     In some implementations, the content of the aluminum component in the proximal aluminum barrier layer  141  varies in the gradient manner. For example, in order to avoid lattice mismatch between the proximal aluminum barrier layer  141  and the active layer  12  and lattice mismatch between the proximal aluminum barrier layer  141  and the indium well layer  142 , from one side of the proximal aluminum barrier layer  141  close to the active layer  12  to one side of the proximal aluminum barrier layer  141  away from the active layer, the content of the aluminum component in the proximal aluminum barrier layer  141  gradually increases first, and then gradually decreases. In some examples, the content of the aluminum component in the proximal aluminum barrier layer  141  gradually increases to a peak value, and then immediately decreases gradually. However, in other examples, the content of the aluminum component in the proximal aluminum barrier layer  141  gradually increases to the peak value, is maintained at the peak value in a middle layered structure, and then gradually decreases. In some implementations, the proximal aluminum barrier layer  141  includes a first sub-layer  1411 , a second sub-layer  1412 , and a third sub-layer  1413 . The process of growing the proximal aluminum barrier layer  141  will be described below with reference to  FIG.  4   ,  FIG.  5   , and  FIG.  6   . 
     S 402 , grow on the active layer a first sub-layer with a gradually increasing content of the aluminum component. 
     As illustrated in part (a) of  FIG.  5   , growth of the N-type semiconductor layer  11  and the active layer  12  in the epitaxial layer  10  is completed. As illustrated in part (b) of  FIG.  5   , the first sub-layer  1411  is grown on the active layer  12 . Reference can be made to  FIG.  6   , which is a schematic diagram illustrating a variation of a content of aluminum component during growth of a proximal aluminum barrier layer  141 . In  FIG.  6   , the horizontal axis represents time (t), and the vertical axis represents the percentage (n %) of a content of component. As can be seen from  FIG.  6   , variation of the content of the aluminum component has three stages: a gradually increasing stage, a maintaining stage, and a gradually decreasing stage. The first sub-layer  1411  corresponds to the gradually increasing stage, and the content of the aluminum component gradually increases when the first sub-layer  1411  is grown. It can be understood that, the content of the aluminum component increases and decreases linearly in  FIG.  6   , however in other implementations, the content of the aluminum component may increase and decrease in a stepwise gradient manner as illustrated in  FIG.  7   , which is a schematic diagram illustrating another variation of a content of aluminum component during growth of the proximal aluminum barrier layer  141 . 
     In some examples, the content of the aluminum component in the first sub-layer  1411  gradually increases from 0 to for example 6%˜12%. For example, the peak value of the content of the aluminum component in the first sub-layer  1411  may be any one of, but not limited to, 6%, 7%, 9%, 10%, 10.5%, or 12%. 
     S 404 , grow on the first sub-layer a second sub-layer with an unchanged content of the aluminum component. 
     As illustrated in part (c) of  FIG.  5   , after the first sub-layer  1411  is grown, the second sub-layer  1412  is grown on the first sub-layer  1411 , and in the second sub-layer  1412 , the content of the aluminum component is maintained at the peak value of the content of the aluminum component in the first sub-layer  1411 . The second sub-layer  1412  corresponds to a second stage in  FIG.  6   , i.e., a stage in which the content of the aluminum component is maintained unchanged. 
     S 406 , grow on the second sub-layer a third sub-layer with a gradually decreasing content of the aluminum component. 
     After the second sub-layer  1412  is grown, a third sub-layer  1413  is grown on the second sub-layer  1412 , as illustrated in part (d) of  FIG.  5   . The third sub-layer  1413  corresponds to a third stage in  FIG.  6   . When the third sub-layer  1413  is grown, the content of the aluminum component gradually decreases. Therefore, the content of the aluminum component gradually decreases from one side of the third sub-layer  1413  close to the active layer  12  to one side of the third sub-layer  1413  away from the active layer  12 . 
     In some implementations, a content of indium component in the indium well layer  142  varies in a gradient manner. For example, in order to avoid lattice mismatch between the indium well layer  142  and the proximal aluminum barrier layer  141  and lattice mismatch between the indium well layer  142  and the distal aluminum barrier layer  143 , the content of the indium component in the indium well layer  142  gradually increases first and then gradually decreases from the side of the indium well layer  142  close to the active layer  12  to one side of the indium well layer  142  away from the active layer  12 . In some implementations, the indium well layer  142  includes a fourth sub-layer  1421  and a fifth sub-layer  1422 . The process of growing the indium well layer  142  will be described below with reference to  FIG.  8   ,  FIG.  9   , and  FIG.  10   : 
     S 602 , grow on the proximal aluminum barrier layer a fourth sub-layer with a gradually increasing content of indium component. 
     As illustrated in part (a) of  FIG.  9   , prior to growth of the fourth sub-layer  1421 , the proximal aluminum barrier layer  141  has been grown, thus as illustrated in part (b) of  FIG.  9    the fourth sub-layer  1421  is grown on the proximal aluminum barrier layer  141 . Reference can be made  FIG.  10   , which is a schematic diagram illustrating a variation of a content of indium component during growth of an indium well layer  142 . As can be seen from  FIG.  10   , the variation of the content of the indium component in  FIG.  10    has two stages: a gradually increasing stage and a gradually decreasing stage. The fourth sub-layer  1421  corresponds to the gradually increasing stage, and the content of the indium component gradually increases when the fourth sub-layer  1421  is grown. It can be understood that the content of the indium component in  FIG.  10    increases and decreases linearly, however in other implementations, the content of the indium component in  FIG.  10    may increase and decrease in a stepwise gradient manner. 
     In some implementations, the content of indium component in the fourth sub-layer  1421  gradually increases from 0 to, for example, 2%˜6%. For example, the peak value of the content of indium component in the fourth sub-layer  1421  may be any one of 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or 6%, but is not limited herein. 
     5604, grow on the fourth sub-layer a fifth sub-layer with a gradually decreasing content of indium component. 
     After the fourth sub-layer  1421  is grown, a fifth sub-layer  1422  is grown on the fourth sub-layer  1421 , as illustrated in part (c) of  FIG.  9   . The fifth sub-layer  1422  corresponds to a second stage in  FIG.  10   . When the fifth sub-layer  1422  is grown, the content of indium component gradually decreases. Therefore, in the fifth sub-layer  1422 , the content of indium component gradually decreases from one side of the fifth sub-layer  1422  close to the active layer  12  to one side of the fifth sub-layer  1422  away from the active layer  12 . 
     It should be understood that, although the growth of the indium well layer  142  in  FIG.  6    is divided into only two main stages, in other implementations, the growth of the indium well layer  142  may also be divided into more stages, for example, a maintaining stage in which the content of the indium component is maintained at a peak may also be inserted between the gradually increasing stage and the gradually decreasing stage. Optionally, the growth of the indium well layer  142  has a gradually increasing stage, a maintaining stage, a gradually increasing stage, a gradually decreasing stage, a maintaining stage, a gradually decreasing stage, and the like in sequence. 
     In some implementations, the content of the aluminum component in the distal aluminum barrier layer  143  varies in a gradient manner, for example, in order to avoid lattice mismatch between the distal aluminum barrier layer  143  and the indium well layer  142 , the content of the aluminum component in the distal aluminum barrier layer  143  gradually increases first and then gradually decreases from one side of the distal aluminum barrier layer  143  close to the active layer  12  to one side of the distal aluminum barrier layer  143  away from the active layer  12 . In some examples, the distal aluminum barrier layer  143  includes a sixth sub-layer  1431  and a seventh sub-layer  1432 . The process of growing the distal aluminum barrier layer  143  will be described below with reference to  FIGS.  11 ,  12 , and  13   . 
     S 702 , grow on the indium well layer a sixth sub-layer with a gradually increasing content of the aluminum component. 
     In part (a) of  FIG.  12   , the indium well layer  142  is grown. A sixth sub-layer  1431  is grown on the indium well layer  142 , as illustrated in part (b) of  FIG.  12   . Reference can be made to  FIG.  13    which is a schematic diagram illustrating a variation of a content of aluminum component during growth of a distal aluminum barrier layer  143 . As illustrated in  FIG.  13   , the variation of the content of the aluminum component has two stages: a gradually increasing stage and a gradually decreasing stage. The sixth sub-layer  1431  corresponds to a gradually increasing stage, and therefore, when the sixth sub-layer  1431  is grown, the content of the aluminum component gradually increases. It should be understood that, although the content of the aluminum component increases and decreases linearly in  FIG.  13   , in other implementations, the content of the aluminum component may increase and decrease in a stepwise gradient manner. 
     In some implementations, the content of the aluminum component in the sixth sub-layer  1431  gradually increases from 0 to, for example, to 4%˜8%. For example, the peak value of the content of the aluminum component in the sixth sub-layer  1431  may be any one of, but not limited to, 4%, 5%, 5.5%, 6%, 6.5%, 7%, or 8%. 
     S 704 , grow on the sixth sub-layer a seventh sub-layer with a gradually decreasing content of the aluminum component. 
     After the sixth sub-layer  1431  is grown, a seventh sub-layer  1432  is grown on the sixth sub-layer  1431  as illustrated in part (c) of  FIG.  12   . The seventh sub-layer  1432  corresponds to a second stage in  FIG.  13   , When the seventh sub-layer  1432  is grown, the content of the aluminum component gradually decreases, and therefore, in the seventh sub-layer  1432 , from one side of the seventh sub-layer  1432  close to the active layer  12  to one side of the seventh sub-layer  1432  away from the active layer  12 , the content of the aluminum component gradually decreases. 
     An LED chip is further provided in the present disclosure. Reference can be made to  FIG.  14    which is a schematic structural diagram of an LED chip. The LED chip  8  includes an epitaxial layer  10  provided in any one of foregoing examples. In addition, the LED chip  8  further includes an electrode, and the electrode specifically includes an N-electrode  81  electrically coupled with an N-type semiconductor layer  11  in the epitaxial layer  10  and a P-electrode  83  electrically coupled with a P-type semiconductor layer  13 . The specific structure of the epitaxial layer  10  have been described in detail above, and will not be repeated herein. It should be understood that, although two chip-electrodes of the LED chip  8  are located on the same side of the epitaxial layer  10  and have a flip-chip structure in  FIG.  14   , in other implementations, other structures may also be prepared based on the epitaxial layer  10 , for example, an LED chip with a normal-chip structure or an LED chip with a vertical structure. 
     In the epitaxial layer, the LED chip and the method for growing an electron-blocking layer provided in implementations, when an electron-blocking layer for blocking electrons from entering a P-type semiconductor layer is prepared, a pumping structure of a barrier layer/well layer/barrier layer can be formed, and holes in the P-type semiconductor layer are injected into an active layer through the pumping structure, thereby improving injection rate of carriers in the active layer, increasing a probability of recombination of electrons and holes, and improving luminescent efficiency of the active layer. Furthermore, a forward voltage of the LED chip can be reduced because a potential barrier of the distal aluminum barrier layer in the electron-blocking layer that is away from the active layer is lower than the potential barrier of the proximal aluminum barrier layer that is closer to the active layer. Furthermore, since the proximal aluminum barrier layer, the indium well layer, and the distal aluminum barrier layer in the electron-blocking layer can all grow in a component-gradient manner, lattice mismatch in the epitaxial layer can be avoided, a defect density of crystal in the epitaxial layer can be reduced, crystal quality can be improved, and therefore the light-emitting efficiency of the LED chip prepared based on the epitaxial layer can be increased. 
     Another alternative implementation is provided in the present disclosure. 
     In order to make advantages and details of the method for growing an electron-blocking layer, the epitaxial layer, and the LED chip provided in foregoing examples clearer to those skilled in the art, the foregoing solutions will be further described in this implementation in conjunction with examples, and reference can be made to  FIG.  15    which is a schematic structural diagram of an epitaxial layer  90 . 
     The epitaxial layer  90  includes a substrate  91 , a buffer layer  92  (or nucleation layer), a GaN intrinsic layer  93 , an N-type GaN layer  94 , an N-type retardation layer  95 , an active layer  96 , an electron-blocking layer  97  and a P-type GaN layer  98  in sequence. In addition, in some implementations, a stress relief layer (SRL) may be further disposed between the N-type retardation layer  95  and the active layer  96 . It should be understood that, when the epitaxial layer  90  is grown, the foregoing layered structures are grown on the substrate  91  according to a sequence of the foregoing layered structures. A growth process of the epitaxial layer  90  will be described below with reference to  FIG.  16    is a schematic flowchart illustrating growing the epitaxial layer  90  and  FIG.  17    is a schematic diagram illustrating a process for growing the epitaxial layer  90 . 
     S 1002 , provide a substrate and place the substrate in a reaction chamber. 
     As illustrated in part (a) of  FIG.  17   , in this implementation, the substrate  91  may include but is not limited to any one of a sapphire substrate, a silicon substrate, and a GaN substrate, and the sapphire substrate  91  is taken as an example herein. It should be understood that, when epitaxial growth is performed by using the substrate  91 , preparation work may be performed before formal growth, for example, preheating, cleaning, and the like are performed on the substrate. For example, the sapphire substrate may be baked at a temperature of 1100° C. and the surface of the substrate  91  is cleaned. 
     In this implementation, the epitaxial layer  90  is grown by a metal-organic chemical vapor deposition (MOCVD) technology, and therefore, the reaction chamber may be an MOCVD reaction chamber. Metal organic sources may include trimethylgallium (TMGa), triethylgallium (TEGa), trimethylindium (TMIn), trimethylaluminum (TMAl). Ammonia (NH3) is used to provide an N source required for growth, silane (SiH4) is used to provide a Si source or germane (GeH4) is used to provide a Ge source in N-type doping; magnetocene (CP2Mg) is used to provide a magnesium source in P-type doping; and at least one of Nitrogen (N2) and hydrogen (H2) can be used as a carrier gas for transmitting an organic source. 
     S 1004 , grow a buffer layer on the substrate. 
     After the substrate  91  is processed, the temperature of the reaction chamber can be reduced to 540° C.˜660° C., and a buffer layer  92  with a thickness of 15 nm is grown, as illustrated in part (b) of  FIG.  17   , where a growth pressure is 100 mbar˜400 mbar. 
     S 1006 , grow a GaN intrinsic layer on the buffer layer. 
     After the buffer layer  92  is grown, a GaN intrinsic layer  93  that is an undoped GaN layer is grown, as illustrated in part (c) of  FIG.  17   . Alternatively, after the buffer layer  92  is grown, the temperature of the reaction chamber may be increased to 950˜1050° C., such that a GaN intrinsic layer  93  with a thickness of 1 um˜3 um is grown, where a growth pressure is 100 mbar˜400 mbar. 
     S 1008 , grow an N-type GaN layer on the GaN intrinsic layer. 
     An N-type GaN layer  94  with a thickness of 1.3 um is grown at a temperature of 1050° C.˜1150° C. and a pressure of 300 mbar˜600 mbar, as illustrated in part (d) of  FIG.  17   . 
     S 1010 , grow an N-type retardation layer on the N-type GaN layer. 
     After the N-type GaN layer  94  is grown, an N-type retardation layer  95  is epitaxially grown, as illustrated in part (e) of  FIG.  17   , where a growth temperature of the N-type retardation layer  95  is about 1050° C.˜1150° C., and a growth pressure is about 100 mbar˜400 mbar. 
     S 1012 , grow an active layer on the N-type retardation layer. 
     After the N-type retardation layer  95  is grown, the active layer  96  continues to be grown, as illustrated in part (f) of  FIG.  17   . In the active layer  96 , a barrier layer and a well layer alternately grow for 5˜15 receptions. The barrier layer is grown under an N2 atmosphere, at a temperature of 800° C.˜900° C. and a pressure of 300 mbar˜600 mbar, and with a thickness of about 8˜15 nm; and the well layer is grown under a N2 atmosphere, at a temperature of 650° C.˜750° C. and a pressure of 300 mbar˜600 mbar with a thickness of 2 nm˜6 nm. 
     S 1014 , grow an electron-blocking layer on the active layer. 
     After the active layer  96  is grown, the temperature of the reaction chamber is increased to be 950° C.˜1050° C., and the pressure is maintained at 100 mbar˜300 mbar, such that an electron-blocking layer  97  is grown on the active layer  96 , where the electron-blocking layer  97  has a growth thickness of 30 nm˜50 nm, as illustrated in part (g) of  FIG.  17   . In this implementation, growth of the electron-blocking layer  97  has three stages, which are growth of a proximal aluminum barrier layer, growth of an indium well layer, and growth of a distal aluminum barrier layer, respectively, as illustrated in  FIG.  18   . The proximal aluminum barrier layer is a proximal AlGaN layer  971 , the indium well layer is an InGaN layer  972 , and the distal aluminum barrier layer is a distal AlGaN layer  973 . 
     Growth processes of three layers of the proximal AlGaN layer  971 , the InGaN layer  972 , and the distal AlGaN layer  973  will be further described with reference to  FIG.  19   . In  FIG.  19   , the horizontal axis represents time (t), the vertical axis represents a percentage of a content of component (n %), a solid line represents a content of Al component, and a dotted line represents a content of In component. 
     First, the content of Al content gradually increases from 0 to 6%˜12%, and in the process of the content of Al component gradually increasing, the first sub-layer  9711  with a gradually increasing content of Al component is grown on the active layer  96 . The first sub-layer  9711  mainly contains AlGaN, however it can be understood that when the content of the Al component is 0, GaN is grown. Therefore, the first sub-layer  9711  contains GaN and AlGaN with an increasing content of the Al component, so that lattice mismatch with a layered structure grown previously (namely, the active layer) can be avoided while the potential barrier is increased. The first sub-layer  9711  has a thickness ranging from 5 nm to 10 nm. Then, the second sub-layer  9712  is grown by maintaining the content of the Al component at the highest content for a period of time. The second sub-layer  9712  has a thickness ranging from 3 nm to 6 nm. In the proximal AlGaN layer  971 , after the content of the Al component reaches the peak, the proximal AlGaN layer  971  will be grown for a period of time by maintaining the content of the Al component at the peak, so that the potential barrier may be increased, thereby increasing an electron-blocking capability. Subsequently, the content of the Al component gradually decreases from the peak value to 0, and a third sub-layer  9713  is grown in the process of the content of the Al component gradually decreasing. The third sub-layer  9713  has a thickness ranging from 5 nm to 10 nm. It can be understood that, after the content of the Al component in AlGaN decreases to 0, AlGaN becomes GaN, and therefore the third sub-layer  9713  mainly contains AlGaN, and GaN exists on the top of the third sub-layer  9713 . It should be understood that, after the third sub-layer  9713  is grown, growth of the proximal AlGaN layer  971  is completed. 
     Then, the InGaN layer  972  is grown on the proximal AlGaN layer  971 . A growth pressure of the InGaN layer  972  ranges from 100 mbar to 300 mbar. First, a content of In component gradually increases from 0 to 2%˜6%, a fourth sub-layer  9721  with an increasing content of the In component is grown in the process of the content of the In component gradually increasing, and the fourth sub-layer  9721  has a thickness ranging from 3 nm to 6 nm. It should be understood that, because the proximal AlGaN layer  971  does not contain In component, InGaN with a gradually increasing content of the In component is grown on the proximal AlGaN layer  971 , so that lattice mismatch and interface polarization may be avoided, and a crystal defect may be reduced. When the content of the In component is 0, GaN is grown, and then when the content of the In component is greater than 0, InGaN is grown. Therefore, the fourth sub-layer  9721  mainly includes InGaN, but also includes a small amount of GaN. Similarly, when the content of the In component reaches a peak value, the content of the In component may gradually decreases to 0, and a fifth sub-layer  9722  with a thickness ranging from 3 nm to 6 nm is grown in the process of decreasing of the content of the In component. In this way, the crystal quality of subsequent In-free layered structure grown on the fifth sub-layer  9722  can be optimized. After the fifth sub-layer  972  is grown, growth of the InGaN layer  972  is completed, and the InGaN layer  972 , serving as a channel layer, improves injection efficiency of holes. 
     Next, a distal AlGaN layer  973  is grown on the InGaN layer  972 . First, also for the purpose of avoiding lattice mismatch, in the process of growing a barrier with an increasing content of the Al component, the content of the Al component gradually increases from 0. In this implementation, the content of the Al component in the distal AlGaN layer  973  is 50%˜70% of the content of the Al component in the proximal AlGaN layer  971 . For example, the peak value of the content of the Al component in the distal AlGaN layer  973  may be between 4%˜8%. A layered structure grown in the process of the content of the Al component gradually increasing is a sixth sub-layer  9731  with a thickness ranging from 5 nm to 10 nm. When the content of Al component reaches the peak value, the content of Al component may gradually decreases to 0, and a 5 μm a seventh sub-layer  9732  with a thickness ranging from 5 nm to 10 nm is grown in the process of content the Al component gradually decreasing. After seventh sublayer  9732  is grown, growth of the distal AlGaN layer  973  is completed, and thus, growth of the electron-blocking layer  97  is completed. 
     S 1016 , grow a p-type GaN layer on the electron-blocking layer. 
     After the electron-blocking layer  97  is grown, the p-type GaN layer  98  is grown with H2 as a carrier gas at a growth temperature of 900° C.˜1050° C. and a growth pressure of 300 mbar˜600 mbar, and the p-type GaN layer  98  has a thickness ranging from 50 nm˜150 nm, as illustrated in part (h) of  FIG.  17   . 
     After the p-type GaN layer  98  is grown, a growth process may be completed by annealing under N2 atmosphere and at a temperature of 650° C.˜750° C. 
     It should be noted that, in the above implementations, when the electron-blocking layer  97  is grown, the content of the Al component and the content of the In component vary in a linear gradient manner, but in other implementations, at least one of the content of the Al component and the content of the In component may vary in a stepwise gradient manner. 
     An LED chip is further provided in the present disclosure. The LED chip includes an epitaxial layer  90 , and an N-electrode, and a P-electrode, where the N-electrode is electrically coupled with an N-type GaN layer  94  in the epitaxial layer  90 , and the P-electrode is electrically coupled with a P-type GaN layer  98  in the epitaxial layer  90 . In addition, a display panel is further provided in the present disclosure. The display panel includes a drive back plate and multiple LED chips, where chip-electrodes of the LED chips are electrically coupled with a drive circuit on the drive back plate, and at least some of the multiple LED chips are prepared based on the epitaxial layer  90 . 
     In the epitaxial layer provided in implementations, growth of the electron-blocking layer is divided into three stages. In a first stage of growth, the content of Al component is controlled to gradually increase, so as to avoiding lattice mismatch with a previous active layer. when the content of the Al component is the highest, continue to grow the electron-blocking layer while maintaining the content of the Al component unchanged, so as to increase a potential barrier and increase an electron-blocking capability. Subsequently, the content of the Al component gradually decreases, such that a first stage of growth is completed. In a second stage of growth, the content of the In component is controlled to gradually increase first and then gradually decrease, such that a channel layer is formed. In a third stage of growth, the content of the Al component is controlled to gradually increase and then gradually decrease. Epitaxial growth with a content of component gradually varying can avoid interface polarization and lattice mismatch, improve crystal quality of material growth, and reduce a potential-barrier voltage. Furthermore, the channel layer is formed to enhance injection efficiency of holes, effectively increase a probability of efficient light-emitting recombination of the electrons and the holes in the active layer, and improve luminescent efficiency. A structure grown though three stages forms with a higher potential-barrier layer/well layer/lower potential-barrier layer, which is also beneficial for forming a hole-injection pumping structure, thereby improving hole injection efficiency of the active layer. 
     In the described epitaxial layer, the LED chip, and the method for growing an electron-blocking layer, an electron-blocking layer is disposed on an active layer, the electron-blocking layer is used to block electrons in the active layer from escaping to a P-type semiconductor layer, thereby improving recombination efficiency of electrons and holes in the active layer, and being beneficial to increasing internal quantum efficiency of the LED chip. Meanwhile, since a hole pumping structure is formed in an electron-blocking layer through a proximal aluminum barrier layer, an indium well layer, and a distal aluminum barrier layer, and the indium well layer serves as a channel layer, injection efficiency of holes into the active layer can be improved, a probability of efficient light-emitting recombination of the electrons and the holes in the active layer is effectively increased, and luminescent efficiency of the LED chip is improved. In addition, since a content of aluminum component in the distal aluminum barrier layer is lower than a content of aluminum component in the proximal aluminum barrier layer, a potential barrier of the distal aluminum barrier layer is lower than a potential barrier of the proximal aluminum barrier layer, which helps to reduce a forward voltage of a device. 
     It should be understood that the application of the present disclosure is not limited to the above implementations, and those skilled in the art can make improvements or modifications according to above descriptions, and all these improvements and modifications shall belong to the scope of protection of the appended claims of the present disclosure.