Patent Publication Number: US-2022231186-A1

Title: Preparation method for resonant cavity light-emitting diode

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2020/130867, filed on Nov. 23, 2020, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of semiconductor technology, and in particular to a preparation method for a resonant cavity light-emitting diode. 
     BACKGROUND 
     Group III nitrides are the third-generation new semiconductor materials after the first-generation and second-generation semiconductor materials such as Si and GaAs. Among them, GaN has many advantages as a wide bandgap semiconductor material, such as high saturation drift speed, high breakdown voltage, excellent carrier transport performance, and ability to form AlGaN, InGaN ternary alloys, AlInGaN quaternary alloys, etc., making it easy to fabricate GaN-based PN junctions. In view of this, GaN-based materials and semiconductor devices have received extensive and in-depth research in recent years. The Metal-organic Chemical Vapor Deposition (MOCVD) technology for growing GaN-based materials has become more and more mature. In terms of semiconductor device research, the research of GaN-based LED, LDs and other optoelectronic devices and GaN-based High Electron Mobility Transistor (HEMT) and other microelectronic devices has made remarkable achievements and great progress. 
     However, in the related art, the light-emitting wavelengths at different positions of the optoelectronic device based on resonant cavity are different, that is, the light-emitting uniformity is poor. 
     In view of this, it is necessary to provide a new preparation method for a resonant cavity light-emitting diode to solve the above technical problems. 
     SUMMARY 
     The purpose of this application is to provide a preparation method for a resonant cavity light-emitting diode, which can improve the uniformity of the light-emitting of the resonant cavity light-emitting diode. 
     In order to achieve the above objective, the first aspect of this application provides a preparation method for a resonant cavity light-emitting diode. 
     A preparation method for a resonant cavity light-emitting diode, comprising: 
     forming a first mirror and a first semiconductor layer on a substrate in sequence; 
     forming an active layer on the first semiconductor layer; and 
     forming a second semiconductor layer and a second mirror on the active layer in sequence, 
     where the preparation method further comprises: planarizing at least one of a first contact surface between the first semiconductor layer and the first mirror, and a second contact surface between the second semiconductor layer and the second mirror. 
     Optionally, forming a second semiconductor layer and a second mirror on the active layer in sequence comprises: 
     forming a second semiconductor material layer on the active layer; 
     obtaining the second semiconductor layer after a surface of the second semiconductor material layer away from the active layer is planarized; and 
     forming the second mirror on the second semiconductor layer, 
     where planarizing at least one of a first contact surface between the first semiconductor layer and the first mirror, and a second contact surface between the second semiconductor layer and the second mirror comprises: 
     planarizing the surface of the second semiconductor material layer away from the active layer. 
     Optionally, before forming the first mirror and the first semiconductor layer on the substrate in sequence, the method further comprises: 
     forming a nucleation layer and a buffer layer on the substrate in sequence. 
     Optionally, forming a first mirror and a first semiconductor layer on a substrate in sequence comprises: 
     forming a first reflective material layer on the substrate; 
     obtaining the first mirror after a surface of the first reflective material layer away from the substrate is planarized; and 
     forming the first semiconductor layer on the first mirror, 
     where planarizing at least one of a first contact surface between the first semiconductor layer and the first mirror, and a second contact surface between the second semiconductor layer and the second mirror comprises: 
     planarizing the surface of the first reflective material layer away from the substrate. 
     Optionally, the first reflective material layer comprises multiple first insulating material layers and second insulating material layers that are alternately arranged. 
     Optionally, before forming the first reflective material layer on the substrate, the method further comprises: 
     forming a nucleation layer and a buffer layer on the substrate in sequence. 
     Optionally, a conductivity type of the first semiconductor layer is opposite to a conductivity type of the second semiconductor layer. 
     Optionally, the first semiconductor layer is an N-type semiconductor layer, the second semiconductor layer is a P-type semiconductor layer, and the active layer includes a multiple quantum well structure. 
     Optionally, the multiple quantum well structure is a periodic structure in which GaN and AlGaN are alternately arranged, or a periodic structure in which GaN and AlInGaN are alternately arranged. 
     Optionally, a material of the first semiconductor layer comprises a group III-V compound, and a material of the second semiconductor layer comprises a group III-V compound. 
     Optionally, the resonant cavity light-emitting diode further comprises a third insulating material layer, a fourth insulating material layer, a first electrode and a second electrode; the third insulating material layer is located on a side of the first mirror away from the second mirror, and the first electrode is located on a side of the third insulating material layer away from the first mirror; and 
     the fourth insulating material layer is located on a side of the second mirror away from the first mirror, and the second electrode is located on a side of the fourth insulating material layer away from the second mirror, the second electrode contacts the second mirror through a hole on the fourth insulating material layer. 
     Optionally, planarizing at least one of a first contact surface between the first semiconductor layer and the first mirror, and a second contact surface between the second semiconductor layer and the second mirror comprises: 
     detecting whether a surface roughness of the first contact surface is within a specified range during the process of planarizing the first contact surface; 
     if so, stopping planarizing the first contact surface to obtain the second semiconductor layer; and 
     if not, continuing planarizing the first contact surface until the surface roughness of the first contact surface falls within a specified range. 
     Optionally, planarizing at least one of a first contact surface between the first semiconductor layer and the first mirror, and a second contact surface between the second semiconductor layer and the second mirror comprises: 
     detecting whether a surface roughness of the second contact surface is within a specified range during the process of planarizing the second contact surface; 
     if so, stopping planarizing the second contact surface to obtain the first mirror; and 
     if not, continuing planarizing the second contact surface until the surface roughness of the second contact surface falls within a specified range. 
     This application also provides another preparation method for a resonant cavity light-emitting diode. 
     A preparation method for a resonant cavity light-emitting diode, comprising: 
     forming a first semiconductor material layer, an active layer, a second semiconductor layer and a second mirror on a substrate in sequence; 
     pasting a supporting plate on the second mirror; 
     turning over an intermediate transition structure comprising the substrate, the first semiconductor material layer, the active layer, the second semiconductor layer, the second mirror and the supporting plate, and peeling off the substrate to expose a third surface of the first semiconductor material layer; 
     planarizing the third surface to obtain a first semiconductor layer; and 
     forming a first mirror on the first semiconductor layer. 
     Optionally, before forming the first semiconductor material layer, the method further comprises forming a nucleation layer and a buffer layer on the substrate in sequence, and 
     after peeling off the substrate, the method further comprises peeling off the nucleation layer and the buffer layer to expose the third surface. 
     Optionally, a conductivity type of the first semiconductor layer is opposite to a conductivity type of the second semiconductor layer. 
     Optionally, the first semiconductor layer is an N-type semiconductor layer, the second semiconductor layer is a P-type semiconductor layer, and the active layer includes a multiple quantum well structure. 
     Optionally, forming a second semiconductor layer and a second mirror comprises: 
     forming a second semiconductor material layer on the active layer; 
     obtaining the second semiconductor layer after a surface of the second semiconductor material layer away from the active layer is planarized; and forming the second mirror on the second semiconductor layer. 
     Optionally, a material of the first semiconductor layer comprises a group III-V compound, and a material of the second semiconductor layer comprises a group III-V compound. 
     Optionally, the resonant cavity light-emitting diode further comprises a third insulating material layer, a fourth insulating material layer, a first electrode and a second electrode; the third insulating material layer is located on a side of the first mirror away from the second mirror, and the first electrode is located on a side of the third insulating material layer away from the first mirror; 
     the fourth insulating material layer is located on a side of the second mirror away from the first mirror, and the second electrode is located on a side of the fourth insulating material layer away from the second mirror, the second electrode contacts the second mirror through a hole on the fourth insulating material layer. 
     Compared with the prior art, this application has the following beneficial effects: since the first contact surface between the first semiconductor layer and the first mirror, and/or the second contact surface between the second semiconductor layer and the second mirror is planarized, the uniformity of the distance between the first mirror and the second mirror can be improved, that is, the uniformity of the cavity length of the resonant cavity composed by the first mirror and the second mirror can be improved, thereby improving the uniformity of light emission of the resonant cavity light-emitting diode. In addition, due to the uniform cavity length of the resonant cavity, this solution only allows light with specific wavelength to be emitted. Compared to improving the sensitive elements in the active layer that affect the emission wavelength, such as In element, the solution of improving the uniformity everywhere in the resonant cavity is simple in process and low in cost. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a flowchart of a preparation method for a resonant cavity light-emitting diode of a first embodiment of this application. 
         FIG. 2  and  FIG. 3  are schematic intermediate structural views corresponding to the processes in  FIG. 1 . 
         FIG. 4  is a schematic cross-sectional view of the resonant cavity light-emitting diode of the first embodiment of this application. 
         FIG. 5  is a flowchart of a preparation method for a resonant cavity light-emitting diode of a second embodiment of this application. 
         FIG. 6  to  FIG. 8  are schematic intermediate views corresponding to processes in  FIG. 5 . 
         FIG. 9  is a schematic cross-sectional view of the resonant cavity light-emitting diode of the second embodiment of this application. 
         FIG. 10  is a flowchart of a preparation method for a resonant cavity light-emitting diode of a third embodiment of this application. 
         FIG. 11  to  FIG. 15  are schematic intermediate views corresponding to processes in  FIG. 10 . 
         FIG. 16  is a schematic cross-sectional view of the resonant cavity light-emitting diode of the third embodiment of this application. 
         FIG. 17  is a schematic cross-sectional view of a resonant cavity light-emitting diode of a fourth embodiment of this application. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In order to make the above objectives, features and advantages of this application more obvious and understandable, specific embodiments of this application will be described in detail below with reference to the accompanying drawings. 
       FIG. 1  is a flowchart of a preparation method for a resonant cavity light-emitting diode of a first embodiment of this application.  FIG. 2  to  FIG. 3  are schematic intermediate views corresponding to processes in  FIG. 1 .  FIG. 4  is a schematic cross-sectional view of the resonant cavity light-emitting diode of the first embodiment of this application. As shown in  FIG. 1 , the preparation method for the resonant cavity light-emitting diode includes the following steps S 101  to S 103 . 
     In step S 101 , forming a nucleation layer  219 , a buffer layer  22 , a first mirror  23 , a first semiconductor layer  24 , an active layer  25 , and a second semiconductor material layer  26  on a substrate  21  in sequence. 
     In this step, as shown in  FIG. 2 , an epitaxial process can be used to sequentially form the nucleation layer  219 , the buffer layer  22 , the first mirror  23 , the first semiconductor layer  24 , the active layer  25 , and the second semiconductor material layer  26  on the substrate  21 . 
     In this embodiment, the material of the substrate  21  is silicon. Of course, the material of the substrate  21  may also be silicon carbide (SiC), gallium nitride (GaN) or sapphire. 
     In this embodiment, the material of the nucleation layer  219  may be a group III-V compound, for example, it may be AlN, or may be GaN, AlGaN, InGaN or AlInGaN. 
     In this embodiment, the material of the buffer layer  22  may be a group III-V compound, for example, it may be GaN, or may be AlN, AlGaN, InGaN, or AlInGaN. 
     In this embodiment, the first mirror  23  is a Bragg mirror. The first mirror  23  is formed by alternately arranging a high refractive index material and a low refractive index material. For example, the first mirror  23  includes but not limited to multiple layers of SiO 2  and TiO 2  that are alternately arranged. 
     In this embodiment, the first semiconductor layer  24  is an N-type semiconductor layer. The material of the first semiconductor layer  24  is a group III-V compound, such as GaN, or AlN, AlGaN, InGaN, or AlInGaN. The doping element of the first semiconductor layer  24  includes at least one of Si ions, Ge ions, Sn ions, Se ions, and Te ions. For example, the doping element of the first semiconductor layer  24  includes Si ions or includes Si ions and Ge ions, but it is not limited thereto. 
     In this embodiment, the active layer  25  includes a multiple quantum well structure. The multiple quantum well structure may be, but is not limited to, a periodic structure in which GaN and AlGaN are alternately arranged, or may be a periodic structure in which GaN and AlInGaN are alternately arranged. 
     In this embodiment, the second semiconductor material layer  26  is a P-type conductive material layer, and the material of the second semiconductor material layer  26  is a group III-V compound, e.g., may be GaN, or may be AlN, AlGaN, InGaN or AlInGaN. The doping element of the second semiconductor material layer  26  includes at least one of Mg ions, Zn ions, Ca ions, Sr ions, and Ba ions, for example, includes Mg ions, or includes Zn ions and Ca ions, but it is not limited thereto. 
     It should be noted that, as shown in  FIG. 2 , the first surface  213  of the second semiconductor material layer  26  away from the substrate  21  may have unevenness. If the second mirror  28  is grown directly on it, it may cause the surface of the second mirror  28  facing the first mirror  23  to be uneven and cause the uniformity of the thickness of the epitaxial layer between the second mirror  28  and the first mirror  23  to be poor. This in turn causes the cavity length of the resonant cavity at different positions to be different, that is, the uniformity of the cavity length of the resonant cavity is poor, resulting in poor uniformity of the light emission of the resonant cavity light-emitting diode. 
     The relationship between the cavity length T of the resonant cavity and the wavelength λ of the light emitted by the resonant cavity light-emitting diode is as follows: 
       λ=2 nT/N  
 
     Where, N is a positive integer. 
     In step S 102 , planarizing the first surface  213  of the second semiconductor material layer  26  that is away from the substrate  21  to obtain a second semiconductor layer  27 , and the first surface  213  is planarized as the second contact surface  214 . 
     In this embodiment, as shown in  FIG. 3 , a dry etching process, a wet etching process, or a mechanical polishing process may be used to planarize the first surface  213  of the second semiconductor material layer  26  that is away from the substrate  21  to obtain the second semiconductor layer  27 . The first surface  213 , after being planarized, becomes a flat second contact surface  214 . 
     In this embodiment, during the process of planarizing the first surface  213 , it can be detected whether the surface roughness of the first surface  213  is within a specified range. 
     If so, stop planarizing the first surface  213 ; if not, continues planarizing the first surface  213  until the surface roughness of the first surface  213  falls within a specified range. 
     In step S 103 , forming the second mirror  28  on the second semiconductor layer  27 . 
     In this embodiment, as shown in  FIG. 4 , the second mirror  28  is formed on the second semiconductor layer  27  by an epitaxial process to form a resonant cavity with the first mirror  23 . The structure of the second mirror  28  is similar to that of the first mirror  23 , both of which are Bragg mirrors. The second mirror  28  is also formed by high refractive index materials and low refractive index materials that are alternately arranged. For example, the second mirror  28  includes multiple layers of alternately arranged high and low refractive index materials, such as SiO 2  and TiO 2  alternately arranged. 
     In this embodiment, since the first surface  213  of the second semiconductor material layer  26  that is away from the substrate  21  is planarized, the second contact surface  214  where the second semiconductor layer  27  contacts the second mirror  28  is flat. The surface of the second mirror  28  facing the first mirror  23  is flat. In this way, the problem of different cavity lengths at different positions of the resonant cavity can be alleviated, that is, the uniformity of the cavity length of the resonant cavity is improved, and uniformity of the thickness of the epitaxial layer between the second mirror  28  and the first mirror  23  is improved, thereby improving the uniformity of light emission of the resonant cavity light-emitting diode. In addition, due to the uniform cavity length of the resonant cavity, this solution only allows light with specific wavelength to be emitted. Compared to improving the sensitive elements in the active layer that affect the emission wavelength, such as In element, the solution of improving the uniformity everywhere in the resonant cavity is simple in process and low in cost. 
       FIG. 5  is a flowchart of a preparation method for a resonant cavity light-emitting diode of a second embodiment of this application.  FIG. 6  to  FIG. 8  are schematic intermediate views corresponding to processes in  FIG. 5 .  FIG. 9  is a schematic cross-sectional view of the resonant cavity light-emitting diode of the second embodiment of this application. As shown in  FIG. 5 , in this embodiment, the preparation method for the resonant cavity light-emitting diode includes the following steps S 501  to S 504 . 
     In step S 501 , forming a nucleation layer  219  and a buffer layer  22  on a substrate  21  in sequence. 
     In this step, as shown in  FIG. 6 , an epitaxial process is used to sequentially form the nucleation layer  219  and the buffer layer  22  on the substrate  21 . 
     In this embodiment, the material of the substrate  21  may be gallium nitride, or silicon, silicon carbide or sapphire. 
     In this embodiment, the material of the nucleation layer  219  may be GaN, or may be AlN, AlGaN, InGaN, or AlInGaN. 
     In this embodiment, the material of the buffer layer  22  may be AlGaN, or GaN, AlN, InGaN, or AlInGaN. 
     In step S 502 , forming a first reflective material layer  215  on the buffer layer  22 . The first reflective material layer  215  includes a first insulating material layer  2151  and a second insulating material layer  2152  that are stacked. 
     In this step, as shown in  FIG. 7 , an epitaxial process is used to form the first reflective material layer  215  on the buffer layer  22 , where the first reflective material layer  215  includes multiple first insulating material layers  2151  and second insulating material layers  2152  that are alternately arranged. The material of the first insulating material layer  2151  may be TiO 2 , and the material of the second insulating material layer  2152  may be SiO 2 , but it is not limited thereto. 
     It should be noted that, as shown in  FIG. 7 , a second surface  216  of the first reflective material layer  215  that is away from the substrate  21  may have unevenness, which will cause the cavity lengths of the resonant cavity at different positions to be different, that is, the uniformity of the cavity length the resonant cavity is poor, and if the first semiconductor layer  24  is grown directly on it, it may cause the surface of the first semiconductor layer  24  facing the first mirror  23  to be uneven and cause the uniformity of the thickness of the epitaxial layer between the second mirror  28  and the first mirror  23  to be poor, resulting in poor uniformity of the light emission of the resonant cavity light-emitting diode. 
     In step S 503 , planarizing the second surface  216  of the first reflective material layer  215  that is away from the substrate  21  to obtain the first mirror  23 . The second surface  216 , after being planarized, becomes a first contact surface  217 . 
     In this embodiment, in the process of planarizing the second surface  216 , it can be detected whether the surface roughness of the second surface  216  is within a specified range, if so, stop planarizing the second surface  216 , if not, continue planarizing the second surface  216  until the surface roughness of the second surface  216  is within a specified range. 
     In this step, as shown in  FIG. 8 , a dry etching process, a wet etching process, or a mechanical polishing process may be used to planarize the second surface  216  of the first reflective material layer  215  that is away from the substrate  21  to obtain the first mirror  23 . The second surface  216 , after being planarized, becomes the flat first contact surface  217 . 
     In step S 504 , forming the first semiconductor layer  24 , the active layer  25 , the second semiconductor layer  27 , and the second mirror  28  on the first mirror  23  in sequence. 
     In this step, as shown in  FIG. 9 , the first semiconductor layer  24 , the active layer  25 , the second semiconductor layer  27 , and the second mirror  28  are sequentially formed on the first mirror  23  using an epitaxial process. 
     The first semiconductor layer  24 , the active layer  25 , the second semiconductor layer  27  in this embodiment and the first semiconductor layer  24 , the active layer  25 , second semiconductor layer  27  in the first embodiment are similar, which is not repeated here again. 
     In this embodiment, as shown in  FIG. 9 , the structure of the second mirror  28  is similar to the structure of the first mirror  23 , and both of them are Bragg mirrors, including multiple layers of SiO 2  and TiO 2  alternately arranged. 
     In this embodiment, since the second surface  216  of the first reflective material layer  215  that is away from the substrate  21  is planarized, the first contact surface  217  of the first mirror  23  in contact with the first semiconductor layer  24  is flat. The surface of the first mirror  23  facing the second mirror  28  is flat. In this way, the problem of different cavity lengths at different positions of the resonant cavity can be improved, that is, the uniformity of the cavity length of the resonant cavity can be improved, and uniformity of the thickness of the epitaxial layer between the second mirror  28  and the first mirror  23  is improved, thereby improving the uniformity of light emission of the resonant cavity light-emitting diode. In addition, due to the uniform cavity length of the resonant cavity, this solution only allows light with specific wavelength to be emitted. Compared to improving the sensitive elements in the active layer that affect the emission wavelength, such as In element, the solution of improving the uniformity everywhere in the resonant cavity is simple in process and low in cost. 
     It should be noted that the first embodiment and the second embodiment can be used in combination, so that the surface of the first mirror  23  facing the second mirror  28  is flat, and at the same time, the surface of the second mirror  28  facing the first mirror  23  is also flat. Therefore, the cavity length uniformity of the resonant cavity can be further improved, and the uniformity of the thickness of the epitaxial layer between the second mirror  28  and the first mirror  23  is better, thereby further improving the uniformity of the luminescence of the resonant cavity light-emitting diode. 
       FIG. 10  is a flowchart of a preparation method for a resonant cavity light-emitting diode of a third embodiment of this application.  FIG. 11  to  FIG. 15  are schematic intermediate views corresponding to processes in  FIG. 10 .  FIG. 16  is a schematic cross-sectional view of a resonant cavity light-emitting diode of a third embodiment of this application. In this embodiment, the preparation method for the resonant cavity light-emitting diode includes the following steps S 1001  to S 1006 . 
     In step S 1001 , forming a nucleation layer  219  and a buffer layer  22  on a substrate  21  in sequence. 
     In this step, as shown in  FIG. 11 , an epitaxial process is used to sequentially form the nucleation layer  219  and the buffer layer  22  on the substrate  21 . 
     In this embodiment, the material of the substrate  21  may be sapphire, or silicon, silicon carbide, or gallium nitride. 
     In this embodiment, the material of the nucleation layer  219  may be InGaN, or may be GaN, AlN, AlGaN or AlInGaN. 
     In this embodiment, the material of the buffer layer  22  may be InGaN, or may be GaN, AlN, AlGaN or AlInGaN. 
     In step S 1002 , forming a first semiconductor material layer  29 , an active layer  25 , a second semiconductor layer  27 , and a second mirror  28  on the buffer layer  22  in sequence. 
     In this embodiment, as shown in  FIG. 12 , the first semiconductor material layer  29 , the active layer  25 , the second semiconductor layer  27 , and the second mirror  28  are sequentially formed on the buffer layer  22  by using an epitaxial process. 
     In this embodiment, the first semiconductor material layer  29  is an N-type semiconductor material layer. The material of the first semiconductor material layer  29  is a group III-V compound, such as GaN, or AlN, AlGaN, InGaN, or AlInGaN. The doping element of the first semiconductor material layer  29  includes at least one of Si ions, Ge ions, Sn ions, Se ions, and Te ions. For example, the doping element of the first semiconductor material layer  29  includes Si ions, or includes Si ions and Ge ions, but it is not limited thereto. 
     In this embodiment, as shown in  FIG. 12 , the second surface  216  of the first semiconductor material layer  29  facing the buffer layer  22  may have unevenness, which may result in the phenomenon that the uniformity of the thickness of the epitaxial layer between the second mirror  28  and the first mirror  23  is poor, resulting in poor uniformity of light emission of the resonant cavity light-emitting diode. 
     In step S 1003 , pasting a supporting plate  211  on the second mirror  28  to obtain an intermediate transition structure  212 . 
     After the above-mentioned step S 1003 , the intermediate transition structure  212  comprises the substrate  21 , the first semiconductor material layer  29 , the active layer  25 , the second semiconductor layer  27 , the second mirror  28  and the supporting plate  211 . Generally, the intermediate transition structure  212  refers to the whole structure including every layer by the moment. 
     In this embodiment, as shown in  FIG. 13 , an adhesive layer  210  may be used to paste the supporting plate  211  on the second mirror  28  to obtain the intermediate transition structure  212 . The adhesion layer  210  and the supporting plate  211  may be insulating materials. The material of the supporting plate  211  may be silicon. Of course, the material of the substrate  21  may also be silicon carbide, gallium nitride or sapphire. 
     In step S 1004 , turning over the intermediate transition structure  212 , and peeling off the substrate  21 , the nucleation layer  219 , and the buffer layer  22  to expose the third surface  218  of the first semiconductor material layer  29 . 
     In this embodiment, as shown in  FIG. 14 , the intermediate transition structure  212  is turned over, and the substrate  21 , the nucleation layer  219 , and the buffer layer  22  are peeled off, so that the third surface  218  of the first semiconductor material layer  29  is exposed to facilitate planarizing. 
     In step S 1005 , planarizing the third surface  218  to obtain the first semiconductor layer  24 , and the third surface  218  becomes a first contact surface  217  after being planarized. 
     In this embodiment, as shown in  FIG. 15 , a dry etching process, a wet etching process or a mechanical grinding process can be used to planarize the third surface  218  so as to obtain the first semiconductor layer  24 . The third surface  218  becomes the flat first contact surface  217  after being planarized. 
     In step S 1006 , forming a first mirror  23  on the first semiconductor layer  24 . 
     In this embodiment, as shown in  FIG. 16 , the first mirror  23  is formed on the first semiconductor layer  24  by using an epitaxial process. 
     In this embodiment, forming a second semiconductor layer  27  and a second mirror  28  may comprise: forming a second semiconductor material layer  26  on the active layer  25 ; obtaining the second semiconductor layer  27  after a surface of the second semiconductor material layer  26  away from the active layer  25  is planarized; and forming the second mirror  28  on the second semiconductor layer  27 . Detailed description about implementation of these steps is similar as description with regard to  FIGS. 2-4 . Repetition is therefore omitted here. 
     In this embodiment, since the third surface  218  of the first semiconductor material layer  29  has been planarized, thus, the first contact face  217  of the first semiconductor layer  24  that is contact with the first mirror  23  is flat. The uniformity of the thickness of the first semiconductor layer  24  is improved, thereby improving the uniformity of the thickness of the epitaxial layer between the second mirror  28  and the first mirror  23 , thereby improving uniformity of the light emission of the resonant cavity light-emitting diode. In addition, since the cavity length of the resonant cavity is uniform, this solution only allows light with specific wavelength to be emitted. Compared to improving the sensitive elements in the active layer that affect the emission wavelength, such as In element, the solution of improving the uniformity everywhere in the resonant cavity is simple in process and low in cost. 
       FIG. 17  is a schematic cross-sectional view of a resonant cavity light-emitting diode of a fourth embodiment of this application. In this embodiment, as shown in  FIG. 17 , the resonant cavity light-emitting diode includes: a first electrode  222 , a third insulating material layer  220 , a first mirror  23 , a first semiconductor layer  24 , an active layer  25 , a second semiconductor layer  27 , a second mirror  28 , a fourth insulating material layer  221 , and a second electrode  223  that are stacked in sequence. 
     In this embodiment, as shown in  FIG. 17 , the second electrode  223  is in contact with the second mirror  28  through the hole on the fourth insulating material layer  221 . 
     The first mirror  23 , the first semiconductor layer  24 , the active layer  25 , the second semiconductor layer  27 , and the second mirror  28  that are sequentially stacked in this embodiment can be prepared using a preparation method for a resonant cavity light-emitting diode described in any of the above embodiments. 
     Although this application is disclosed as above, but it is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of this application. Therefore, the protection scope of this application should be subject to the scope defined by the claims.