Abstract:
A high-brightness light-emitting diode with surface microstructure and preparation and screening methods thereof are provided. The ratio of total roughened surface area of light transmission surface of a light emitting diode to vertically projected area is greater than 1.5, and the peak density of light transmission surface is not less than 0.3/um 2 . The higher the ratio of total roughened surface area of an epitaxial wafer to vertically projected area and the higher the number of peak over the critical height within a unit area, the more beneficial to improve light extraction efficiency of the epitaxial wafer. As a result, light extraction efficiency of the epitaxial wafer is greatly improved.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of, and claims priority to, PCT/CN2015/070387 filed on Jan. 9, 2015, which claims priority to Chinese Patent Application No. 201410138259.2 filed on Apr. 8, 2014. The disclosures of these applications are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    Light-emitting diode is a semiconductor P-N junction diode; when a forward voltage is applied to both ends of a P-N junction, the current carriers are excited from low-energy state to high-energy state and are in an unstable state, and when the carriers return to low-energy state and recombination is to occur, according to the conservation of energy theorem, excessive energy is released in the form of photons. External quantum efficiency of light emitting diode is the key to improve the light emitting diode luminous efficiency, and depends on the internal quantum efficiency of epitaxial materials and the light extraction efficiency of epitaxial wafer. Now breakthroughs have been made in precise control of epitaxial growth, doping concentration and reduction of dislocations, and internal quantum efficiency of light emitting diode has been already very high, therefore, the light extraction efficiency of epitaxial wafer will determine the luminous efficiency of light emitting diode to a great extent. 
       SUMMARY 
       [0003]    Light extraction efficiency of epitaxial wafers is typically increased by roughening the surface which reduces the reflection by light diffusion while causing no damage to the electrical and optical properties of the material. Surface roughening mainly functions to increase the transmittance; it changes the direction of the light meeting total reflection law, then in another surface the light transmits the interface when emitting back to the original surface, thus preventing reflecting. Reflection path of photons is enclosed in the surface micro structure, therefore, the photons emitted by the active layer can be effectively extracted. Common types of roughening include periodic roughening and random roughening. The latter is usually to control the roughness of the light emitting surface by chemical etching method so to break the total reflection effect of light emitting surface. 
         [0004]    The inventors of the present disclosure have realized that the quality of the product prepared by the widespread chemical roughening is not as high as expected, and no direct method for determining whether epitaxial wafer has a high luminous intensity is available, and instead, optimization conditions are decided generally based on several groups of luminance data from try &amp; error tests under different process conditions, which cannot determine whether a roughened surface structure has been at a state most conducive to light extraction, and therefore, the capability to define the surface microstructure will be very beneficial to improve the quality of light emitting diode products. 
         [0005]    Some embodiments of the present disclosure aim to provide a high brightness light emitting diode with surface microstructure and preparation method and screening method thereof, so as to improve the yield of high brightness light emitting diode, while addressing the problem of failing to determine the quality of the surface microstructure existing in the prior art. 
         [0006]    To solve the above problems, the following technical scheme is adopted according to some embodiments: a high brightness light emitting diode with a surface microstructure, the light transmission surface of the light emitting diode has a surface microstructure, and the ratio of total roughened surface area of light transmission surface of a light emitting diode to vertically projected area is not less 1.5. 
         [0007]    Further, the peak density of the light transmission surface is not less than 0.3/um 2 . 
         [0008]    Further, the layer of the light transmission surface is Al doped GaInP layer or Mg doped GaP layer, and in Al doped GaInP layer, the mol ratio of Al to GaInP is 0.67-1.5. 
         [0009]    A preparation method of the high brightness light emitting diode is provided, and the preparation process of the surface microstructure of the light emitting diode comprises the following steps: 
         [0010]    (1) have the light transmission surface of the epitaxial wafer of the light emitting diode requiring roughening exposed, and protect the light transmission surface requiring no roughening with photoresist or metal; 
         [0011]    (2) prepare roughening solution as per the following dose proportion in weight percentage and with the following components: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 CH 3 COOH 
                 30~50% 
               
               
                   
                 HF 
                 40~60% 
               
               
                   
                 H 2 SO 4   
                 0~2% 
               
               
                   
                 HNO 3   
                  0~20% 
               
               
                   
                 H 3 PO 4   
                  0~10% 
               
               
                   
                   
               
             
          
         
       
     
         [0012]    (3) dip the epitaxial wafer processed by Step (1) in the roughening solution prepared by Step (2) for 1-8 min and then take out and dry the epitaxial wafer for subsequent preparation of said light emitting diode with surface microstructure. 
         [0013]    Further, the epitaxial wafer processed by Step (1) comprises a high reflection metal surface with electric contact and mirror system, and bonding metal is evaporated over said mirror system and achieves the bonding effect by the application of high temperature and high pressure. 
         [0014]    Further, the high temperature is 250-350° C. and the high pressure is 60-200 KPa. 
         [0015]    A method to screen the high brightness light emitting diode is provided, comprising the following steps: 
         [0016]    (1) select epitaxial wafer with surface roughened; 
         [0017]    (2) measure the total roughened surface area of the light transmission surface on the epitaxial wafer chosen in Step (1); 
         [0018]    (3) calculate the ratio of total roughened surface area to vertically projected area; 
         [0019]    (4) screen the epitaxial wafers with the ratio of total roughened surface area to vertically projected area being not less than 1.5; 
         [0020]    (5) prepare light emitting diodes with the epitaxial wafers screened by Step (4). 
         [0021]    Further, the preparation method of epitaxial wafer is: depositing in order above an epitaxial substrate a buffer layer, an n-electrical cladding, an n-cladding, a multilayer quantum well structure (MQW), a p-cladding and a p-electrical cladding so to finish the growth of epitaxial layer structure. 
         [0022]    Further, the preparation method of a light emitting diode with surface microstructure and with the n-cladding on the top based on the epitaxial wafer prepared by the above method comprises the following steps: 
         [0023]    (1) fabricate a highly reflective metal surface with electric contact and mirror system on the p-electrical cladding of the epitaxial wafer, and a dielectric layer can be added to prepare an omnibearing reflective mirror system to improve reflectivity; 
         [0024]    (2) evaporate bonding metal over the mirror system and have the bonding metal fit with a conductive substrate and then high temperature and high pressure are applied to realize bonding effect; 
         [0025]    (3) When the bonding is completed, remove the epitaxial substrate by etching till the n-electrical cladding is exposed; 
         [0026]    (4) fabricate N electrode on the exposed epitaxial layer and define a main light emitting area; 
         [0027]    (5) have the surface of the n-electrical cladding requiring roughening exposed, and protect the surface requiring no roughening with photoresist or metal, including the vicinity of the electrode and the main light emitting area, to finally obtain roughening pretreated wafer; 
         [0028]    (6) prepare roughening solution containing the solutions of CH 3 COOH, HF, H 2 SO 4 , HNO 3  and H 3 PO 4  in different dosage; 
         [0029]    (7) dip the roughening pretreated wafer processed by Step (5) in the roughening solution prepared by Step (6) for 2-3 min. and then take it out, and the light emitting diode with surface microstructure and with n-cladding on the top, also called surface roughened epitaxial wafer, is obtained. 
         [0030]    The present disclosure also provides a method to screen the above high brightness light emitting diode, comprising the following steps: 
         [0031]    (1) select epitaxial wafer with surface roughened; 
         [0032]    (2) measure the total roughened surface area of the light transmission surface on the epitaxial wafer chosen in Step (1); 
         [0033]    (3) calculate the ratio of total roughened surface area to vertically projected area; 
         [0034]    (4) screen the epitaxial wafers with the ratio of total roughened surface area to vertically projected area not less than 1.5; 
         [0035]    (5) prepare light emitting diodes with the epitaxial wafers screened by Step (4). 
         [0036]    The surface microstructure of the light-emitting diode according to some embodiments disclosed herein can be obtained by surface roughening by chemical solution, that is, a roughened surface is formed on the epitaxial wafer of the light emitting diode; surface roughening is beneficial to improve light extraction efficiency of the epitaxial wafer, and the steep the facial angle of the surface microstructure and the more peak number on the surface is, the more easily the light shot below in various angles is transmitted through the surface microstructure, thus improving light extraction efficiency; poorly roughened surface has gentle and sparse facial angle, which easily reflects small-angle light or right-angle light back to the inside of the structure, and accordingly, light extraction efficiency is decreased. 
         [0037]    Some embodiments disclosed herein define the surface microstructure of the light emitting diode epitaxial wafer and find out the relation between the optimal light intensity and the surface microstructure of the epitaxial wafer, the details of which comprise the following three aspects: 
         [0038]    (1) The higher the number of peak over the critical height within a unit area on the epitaxial wafer is, the more beneficial is to improve the light extraction efficiency of the epitaxial wafer, and especially when the peak density of the roughened surface of the epitaxial wafer is not less than 0.3/μm 2 , light extraction efficiency of the epitaxial wafer is greatly improved and the luminance of the light emitting diode is increased; 
         [0039]    (2) The higher the ratio of total roughened surface area to an epitaxial wafer according to some embodiments of the present disclosure to vertically projected area is, the more beneficial is to improve the light extraction efficiency of the epitaxial wafer, and especially when the ratio of total roughened surface area of to vertically projected area is not less than 1.5, light extraction efficiency of the epitaxial wafer is greatly improved; 
         [0040]    (3) The n-cladding of the epitaxial wafer is Al doped GaInP layer, and the mol ratio of Al to GaInP is between 1.4 and 1.6, and so chemical roughening method can help obtain good surface microstructure, that is, light extraction efficiency of the epitaxial wafer can be greatly improved. 
         [0041]    The screening method according to some embodiments disclosed herein can make direct judgement of the quality of the light intensity by the roughness of light transmission surface, and is characterized by high screening accuracy and efficiency. 
         [0042]    In another aspect, a light-emitting system is provided including a plurality of LEDs described above. The light-emitting system can be, for example, a display, a signage, a lighting apparatus, etc. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]      FIG. 1  is a scatter plot of data related to the change of roughening ratio of samples 1-4 with that of the ratio of specific surface area to vertically projected area; 
           [0044]      FIG. 2  is a scatter plot of data related to the change of brightness after roughening of samples 5-8 with that of the ratio of specific surface area to vertically projected area; 
           [0045]      FIG. 3  is a scatter plot of data related to the change of roughening ratio of samples 9-12 with that of the dosage of Al doped; and 
           [0046]      FIG. 4  is a scatter plot of data related to the change of brightness after roughening of samples 13-16 with that of the ratio of specific surface area to vertically projected area. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    In some embodiments, the roughened surface of the epitaxial wafer after roughening is just the surface with microstructure, and the total roughened surface area of the epitaxial wafer is also called specific surface area. In some the embodiments of the disclosure, the equipment used for testing the light intensity of samples is BRUKER AFM, and the single-point probe test is performed at 20-350 mA. 
         [0048]    The pretreatment of the epitaxial wafer prior to roughening comprises the following steps according to some embodiments: 
         [0049]    (1) fabricate a high reflection metal surface with electric contact and mirror system on the p-electrical cladding of the epitaxial wafer, and a dielectric layer can be added to prepare an omnibearing reflective mirror system to improve reflectivity; 
         [0050]    (2) evaporate bonding metal over the mirror system and have the bonding metal fit with a conductive substrate and then high temperature and high pressure are applied to realize bonding effect; 
         [0051]    (3) following the bonding, remove the epitaxial substrate by etching till the n-electrical cladding is exposed; 
         [0052]    (4) fabricate N electrode on the exposed epitaxial layer and define a main light emitting area; a wafer ready for roughening is finally formed. 
       Embodiment 1 
       [0053]    Four samples are prepared for Embodiment 1, and all are the light emitting diode with surface microstructure and with n-cladding on the top and share the basically same structure, and the same growth method of the epitaxial wafer: depositing a buffer layer and a n-electrical cladding over the epitaxial substrate and then a n-cladding, further depositing a multilayer quantum well (MQW) structure above the n-cladding, followed by a p-cladding deposited on the MQW structure and finally an electrical cladding, thereby completing the growth of the epitaxial layer structure; the difference between the samples 1-4 is that each respective functional layer is made of different materials, so that samples 1-4 emits light with different wavelengths, and the components of specific functional layers of samples 1-4 are provided in Table 1 below: 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Components of functional layers of samples 1-4 
               
             
          
           
               
                   
                 Layer Material 
               
             
          
           
               
                   
                   
                   
                 N-elec- 
                   
                   
                   
               
               
                   
                 Sub- 
                 Buffer 
                 trical 
                 n- 
                   
                 p- 
               
               
                 No. 
                 strate 
                 layer 
                 cladding 
                 cladding 
                 MQW 
                 cladding 
               
               
                   
               
               
                 Sam- 
                 GaAs 
                 GaAs 
                 n-GaAs 
                 n-AlGaInP 
                 InGaP/ 
                 p-GaP 
               
               
                 ple 1 
                   
                   
                   
                   
                 AlGaInP 
               
               
                 Sam- 
                 GaAs 
                 GaAs 
                 n-GaAs 
                 n-AlGaInP 
                 AlGaInP/ 
                 p-GaP 
               
               
                 ple 2 
                   
                   
                   
                   
                 AlGaInP 
               
               
                 Sam- 
                 GaAs 
                 GaAs 
                 n-GaAs 
                 n-AlGaAs 
                 AlGaAs/ 
                 p-GaP 
               
               
                 ple 3 
                   
                   
                   
                   
                 AlGaAs 
               
               
                 Sam- 
                 Al 2 O 3   
                 AlN 
                 — 
                 n-GaN 
                 InGaN/ 
                 p-GaN 
               
               
                 ple 4 
                   
                   
                   
                   
                 GaN 
               
               
                   
               
             
          
         
       
     
         [0054]    After completion of the growth of the epitaxial wafer of samples 1-4, the epitaxial wafer can be prepared into the wafer ready for roughening and finally perform surface roughening to form samples 1-4 with surface microstructure. 
         [0055]    The roughening of samples 1-4 is basically the same, all comprising the following steps: 
         [0056]    (1) have the light transmission surface of samples 1-4 requiring roughening exposed, and protect the light transmission surface requiring no roughening with photoresist or metal; 
         [0057]    (2) prepare the first roughening solution in weight percentage and with the following components: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 CH 3 COOH 
                 30% 
               
               
                   
                 HF 
                 60% 
               
               
                   
                 H 2 SO 4   
                 2% 
               
               
                   
                 HNO 3   
                 5% 
               
               
                   
                 H 3 PO 4   
                 3% 
               
               
                   
                   
               
             
          
         
       
     
         [0058]    Prepare the second roughening solution with a concentration of 40% NaOH. 
         [0059]    (3) dip the sample 1-3 processed by Step (1) in the first roughening solution prepared by Step (2) for 2 min., dip sample 4 in the second roughening solution for 2 min. and then take out and dry samples 1-4 respectively for subsequent preparation of the light emitting diode with surface microstructure. Luminous intensity tests have been carried out to samples 1-4 and the testing results are shown in Table 2: 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Measurements and luminescence property of the 
               
               
                 surface microstructure of samples 1-4 
               
             
          
           
               
                   
                 No. 
               
             
          
           
               
                 Measurements 
                 Sample 1 
                 Sample 2 
                 Sample 3 
                 Sample 4 
               
               
                   
               
             
          
           
               
                 Specific surface area 
                 175 
                 237 
                 153 
                 202 
               
               
                 (μm 2 ) 
               
               
                 Ratio of specific 
                 1.75 
                 2.37 
                 1.53 
                 2.02 
               
               
                 surface area to 
               
               
                 vertically projected 
               
               
                 area (100 μm 2 ) 
               
               
                 Average critical 
                 662 
                 711 
                 452 
                 683 
               
               
                 height of roughened 
               
               
                 surface (nm) 
               
               
                 No. of peak over 
                 58 
                 62 
                 31 
                 65 
               
               
                 average critical 
               
               
                 height 
               
               
                 Peak density 
                 0.58 
                 0.62 
                 0.31 
                 0.65 
               
               
                 Brightness before 
                 383 mcd 
                 88 mW 
                 108 mW 
                 223 mW 
               
               
                 roughening 
               
               
                 Brightness after 
                 678 mcd 
                 217 mW 
                 160 mW 
                 480 mW 
               
               
                 roughening 
               
               
                 Roughening ratio = 
                 1.77 
                 2.46 
                 1.48 
                 2.15 
               
               
                 mcd before 
               
               
                 roughening/mcd 
               
               
                 after roughening 
               
               
                   
               
             
          
         
       
     
         [0060]    As influenced by the sensitivity of human eyes towards wavelength, the brightness of the light of different wavelengths also differs, and therefore, the absolute value of the brightness of the light of different wavelengths cannot be directly compared. In this Embodiment 1, the quality of the roughened surface should be judged by the roughening ratios before and after roughening, and as revealed in the above Table 2, the sample with higher roughening ratio has a higher ratio of specific surface area to vertically projected area, that is, the higher the roughening ratio is, the better the roughening effect of the sample is, and in turn, the higher the ratio of specific surface area to vertically projected area is, the higher the ratio of brightness before and after roughening is, and the present disclosure considers that when the ratio of total roughened surface area to vertically projected area of a sample is not less than 1.5, the sample has a good light intensity, and therefore, this method can be applied to screen high brightness light emitting diode. 
       Embodiment 2 
       [0061]    Four samples are prepared for Embodiment 2, namely, samples 5-8, and share a same preparation method, specifically: depositing a buffer layer (GaAs) and an electrical cladding over the epitaxial substrate and then a n-cladding (n-GaAs), further depositing a multilayer quantum well (MQW) structure (InGaP/AlGaInP) above the n-cladding, followed by a p-cladding (p-GaP) deposited on the MQW structure and finally an electrical cladding, thereby completing the growth of the epitaxial layer structure; after the completion of the growth of the epitaxial wafer of samples 5-8, the epitaxial wafer can be prepared into the wafer ready for roughening and finally perform surface roughening to form samples 5-8 with surface microstructure. 
         [0062]    The roughening of samples 5-8 is basically the same, all comprising the following steps: 
         [0063]    (1) have the light transmission surface of samples 5-8 requiring roughening exposed, and protect the light transmission surface requiring no roughening with photoresist or metal; 
         [0064]    (2) prepare roughening solution as per the following dose proportion in weight percentage and with the following components: 30% CH 3 COOH, 60% HF, 2% H 2 SO 4 , 5% HNO 3  and 3% H 3 PO 4 ; 
         [0065]    (3) dip the samples 5-8 processed by Step (1) in the roughening solution prepared by Step (2) and then take out and dry samples 13-16 for subsequent preparation of the light emitting diode with surface microstructure. 
         [0066]    The difference between the samples 5-8 is that the roughening time of samples 5-8 in Step (3) gradually shortens, 3 min. for sample 5, 2.5 min. for sample 6, 2 min. for sample 7 and 1.5 min. for sample 8. 
         [0067]    Luminous intensity tests have been carried out to samples 5-8 and the testing results are shown in Table 3: 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Measurements of the surface microstructure of samples 5-8 
               
             
          
           
               
                   
                 No. 
               
             
          
           
               
                 Measurements 
                 Sample 5 
                 Sample 6 
                 Sample 7 
                 Sample 8 
               
               
                   
               
             
          
           
               
                 Specific surface area 
                 188 
                 172.2 
                 156.1 
                 132.8 
               
               
                 (μm 2 ) 
               
               
                 Ratio of specific 
                 1.88 
                 1.722 
                 1.561 
                 1.328 
               
               
                 surface area to 
               
               
                 vertically projected 
               
               
                 area (100 μm 2 ) 
               
               
                 Average critical 
                 646 
                 563 
                 463 
                 359 
               
               
                 height of roughened 
               
               
                 surface (nm) 
               
               
                 No. of peak over 
                 55 
                 60 
                 51 
                 47 
               
               
                 average critical height 
               
               
                 Peak density (μm −2 ) 
                 0.55/um 2   
                 0.6/um 2   
                 0.51/um 2   
                 0.47/um 2   
               
               
                 Brightness before 
                 365 
                 365 
                 365 
                 365 
               
               
                 roughening (mcd) 
               
               
                 Brightness after 
                 620.5 
                 613.2 
                 591.3 
                 565.7 
               
               
                 roughening (mcd) 
               
               
                 Roughening ratio = mcd 
                 1.70 
                 1.68 
                 1.62 
                 1.55 
               
               
                 before roughening/mcd 
               
               
                 after roughening 
               
               
                   
               
             
          
         
       
     
         [0068]    The data from Tables 2 and 3 show that the light intensity of the epitaxial wafer has little to do with the material of the epitaxial wafer itself, but mainly related to microstructure of the light transmission surface of the epitaxial wafer, and the light intensity of the epitaxial wafer increases with the ratio of specific surface area to vertically projected area of the light transmission area, especially when the ratio is not less than 1.5 as well as that the peak density of the sample is not less than 0.34 μm 2 , the epitaxial wafer has a high light intensity. 
       Embodiment 3 
       [0069]    Four samples are prepared for Embodiment 3, namely, samples 9-12 and all are of epitaxial wafer in vertical structure, and share a same preparation method, specifically: depositing a buffer layer (GaAs) and an electrical cladding over the epitaxial substrate and then a n-cladding (Al X (GaInP) X ), further depositing a multilayer quantum well (MQW) structure (InGaP/AlGaInP) above the n-cladding, followed by a p-cladding (p-GaP) deposited on the MQW structure and finally an electrical cladding, thereby completing the growth of the epitaxial layer structure; after the completion of the growth of the epitaxial wafer of samples 9-12, the epitaxial wafer can be prepared into the wafer ready for roughening and finally perform surface roughening to form samples 9-12 with surface microstructure. 
         [0070]    The roughening of samples 9-12 is basically the same, all comprising the following steps: 
         [0071]    (1) have the light transmission surface of samples 9-12 requiring roughening exposed, and protect the light transmission surface requiring no roughening with photoresist or metal; 
         [0072]    (2) prepare roughening solution as per the following dose proportion in weight percentage and with the following components: 30% CH 3 COOH, 60% HF, 2% H 2 SO 4 , 5% HNO 3  and 3% H 3 PO 4 ; 
         [0073]    (3) dip the samples 9-12 processed by Step (1) in the roughening solution prepared by Step (2) and then take out and dry samples 13-16 for subsequent preparation of the light emitting diode with surface microstructure. 
         [0074]    The difference between samples 9-12 is that the dose proportion of Al in the epitaxial layer structure is different; the roughened n-cladding layer is made of GaInP, and Al doped GaInP is a material combining III-V elements, and by controlling the proportion of family III Al and family V GaInP during the growth process of the epitaxial structure, samples 9-12 are obtained. Specific contents of Al are shown in Table 4: 
         [0075]    Luminous intensity tests have been carried out to samples 9-12 and the testing results are shown in Table 4: 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Testing results of components and properties of 
               
               
                 n-cladding of samples 9-12 
               
             
          
           
               
                   
                 Measurements 
               
             
          
           
               
                   
                   
                   
                   
                 Ratio of 
               
               
                   
                   
                   
                   
                 luminance 
               
               
                   
                   
                 Luminance 
                 Luminance 
                 after 
               
               
                   
                 n-cladding 
                 before 
                 after 
                 roughening 
               
               
                   
                 material 
                 roughening 
                 roughening 
                 to before 
               
               
                 No. 
                 component 
                 (mcd) 
                 (mcd) 
                 roughening 
               
               
                   
               
               
                 Sample 9 
                 Al 0.4 (GaInP) 0.6   
                 271 
                 475 
                 1.75 
               
               
                 Sample 10 
                 Al 0.5 (GaInP) 0.5   
                 280 
                 495 
                 1.77 
               
               
                 Sample 11 
                 Al 0.6 (GaInP) 0.4   
                 285 
                 489 
                 1.72 
               
               
                 Sample 12 
                 Al 0.7 (GaInP) 0.3   
                 262 
                 430 
                 1.64 
               
               
                   
               
             
          
         
       
     
         [0076]    As shown in Table 4 above, when the mol ratio of Al to GaInP is between 0.67 and 1.5, the light intensities of the samples are high. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Characterization data of roughened surface of samples 9-12 
               
             
          
           
               
                   
                 Measurements 
               
             
          
           
               
                   
                   
                 Ratio of specific 
                   
                   
               
               
                   
                   
                 surface area to 
                 No. of peak 
               
               
                   
                 Specific 
                 vertically 
                 over average 
               
               
                   
                 surface 
                 projected area 
                 critical 
                 Peak 
               
               
                 No. 
                 area (μm 2 ) 
                 (100 μm 2)   
                 height 
                 density  
               
               
                   
               
               
                 Sample 9 
                 167 
                 1.67 
                 52 
                 0.52 
               
               
                 Sample 10 
                 184 
                 1.84 
                 58 
                 0.58 
               
               
                 Sample 11 
                 155 
                 1.55 
                 49 
                 0.49 
               
               
                 Sample 12 
                 123 
                 1.23 
                 41 
                 0.41 
               
               
                   
               
             
          
         
       
     
         [0077]    The data from Tables 4 and 5 show that light intensities of samples 9-11 are high, especially that of sample 10 is as high as 495mcd, and property data results in Table 4 are consistent with the samples in Table 5 selected by the screening method based on that the ratio of specific surface area to vertically projected area of the light transmission surface is not less than 1.5, indicating that the screening method provided according to some embodiments of the present disclosure is proper. 
       Embodiment 4 
       [0078]    Four samples are prepared for Embodiment 2, namely, samples 13-16, and share the same component structure and preparation method, specifically: depositing a buffer layer (GaAs) and an electrical cladding over the epitaxial substrate and then a n-cladding (Al 0.5 (GaInP) 0.5 ), further depositing a multilayer quantum well (MQW) structure (InGaP/AlGaInP) above the n-cladding, followed by a p-cladding (p-GaP) deposited on the MQW structure and finally a p-electrical cladding, thereby completing the growth of the epitaxial layer structure; after the completion of the growth of the epitaxial wafer of samples 13-16, the epitaxial wafer can be prepared into the wafer ready for roughening and finally perform surface roughening to form samples 13-16 with surface microstructure. 
         [0079]    The roughening of samples 13-16 is basically the same, all comprising the following steps: 
         [0080]    (1) have the light transmission surface of samples 13-16 requiring roughening exposed, and protect the light transmission surface requiring no roughening with photoresist or metal; 
         [0081]    (2) prepare roughening solution as per the following dose proportion in weight percentage and with the following components: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 CH 3 COOH 
                 30~50% 
               
               
                   
                 HF 
                 40~60% 
               
               
                   
                 H 2 SO 4   
                 0~2% 
               
               
                   
                 HNO 3   
                  0~20% 
               
               
                   
                 H 3 PO 4   
                  0~10% 
               
               
                   
                   
               
             
          
         
       
     
         [0082]    (3) dip the samples 13-16 processed by Step (1) in the roughening solution prepared by Step (2) and then take out and dry samples 13-16 for subsequent preparation of the light emitting diode with surface microstructure. 
         [0083]    The difference between samples 13-16 is that the dose proportion of roughening solutions for processing the samples by the preparation method for the surface microstructure varies. See Table 6 for the specific dose proportion: 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Dose proportion of roughening solution for samples 13-16 
               
             
          
           
               
                   
                 Solution dose proportion 
               
             
          
           
               
                 No. 
                 CH 3 COOH 
                 HF 
                 H 2 SO 4   
                 HNO 3   
                 H 3 PO 4   
               
               
                   
               
             
          
           
               
                 Sample 13 
                 50% 
                 50% 
                 0% 
                 0% 
                 0% 
               
               
                 Sample 14 
                 40% 
                 60% 
                 0% 
                 0% 
                 0% 
               
               
                 Sample 15 
                 30% 
                 60% 
                 2% 
                 5% 
                 3% 
               
               
                 Sample 16 
                 40% 
                 40% 
                 2% 
                 10% 
                 8% 
               
               
                   
               
             
          
         
       
     
         [0084]    Luminous intensity tests have been carried out to samples 13-16 and the testing results are shown in Table 7: 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Measurements of samples 13-16 
               
             
          
           
               
                   
                 Meas. 
               
             
          
           
               
                   
                   
                   
                 Roughening 
                   
                   
                   
                   
               
               
                   
                   
                   
                 ratio = 
                   
                 Ratio of specific 
                 No. of 
               
               
                   
                 Luminance 
                 Luminance 
                 mcd before 
                 Spec. 
                 surface area 
                 peak over 
               
               
                   
                 before 
                 after 
                 roughening/ 
                 surface 
                 to vertically 
                 average 
                 Peak 
               
               
                   
                 roughening 
                 roughening 
                 mcd after 
                 area 
                 projected area 
                 critical 
                 density 
               
               
                 No. 
                 (mcd) 
                 (mcd) 
                 roughening 
                 (μm 2 ) 
                 (100 μm 2 ) 
                 height 
                 (μm −2 ) 
               
               
                   
               
             
          
           
               
                 Sam- 
                 375 
                 628 
                 1.68 
                 169.6 
                 1.696 
                 55 
                 0.55 
               
               
                 ple 13 
               
               
                 Sam- 
                 377 
                 630 
                 1.68 
                 172.6 
                 1.726 
                 53 
                 0.53 
               
               
                 ple 14 
               
               
                 Sam- 
                 372 
                 615 
                 1.65 
                 153.3 
                 1.533 
                 58 
                 0.58 
               
               
                 ple 15 
               
               
                 Sam- 
                 373 
                 606 
                 1.63 
                 142.2 
                 1.422 
                 52 
                 0.52 
               
               
                 ple 16 
               
               
                   
               
             
          
         
       
     
         [0085]    As revealed by Table 7, n-cladding layer made of Al (GaInP) can obtain good roughening effect with roughening solutions with different dose proportions, improving the quality of the epitaxial wafer. 
         [0086]    A method to screen the high brightness light emitting diode, comprising the following steps: 
         [0087]    (1) select epitaxial wafer with surface roughened; 
         [0088]    (2) measure the total roughened surface area of the light transmission surface on the epitaxial wafer chosen in Step (1); 
         [0089]    (3) calculate the ratio of total roughened surface area to vertically projected area; 
         [0090]    (4) screen the epitaxial wafers with the ratio of total roughened surface area to vertically projected area not less than 1.5; 
         [0091]    (5) prepare light emitting diodes with the epitaxial wafers screened by Step (4). 
         [0092]    Samples selected among the 16 samples in the above embodiments 1-4 by the above screening method are: sample 1, sample 2, sample 3, sample 4, sample 5, sample 6, sample 7, sample 9, sample 10, sample 11, sample 12, sample 13, sample 14 and sample 15, consistent with the results of luminance testing, that is, all the epitaxial wafers with the ratio of total roughened surface area to vertically projected area not less than 1.5 have higher light intensity under the same embodiment; further, the screening method based on that the peak density of the light transmission surface is not less than 0.3/um 2  can also be employed, and the screening result is that: sample 1, sample 2, sample 3, sample 4, sample 5, sample 6, sample 7, sample 9, sample 10, sample 11, sample 12, sample 13, sample 14 and sample 15, consistent with the results by the screening method based on that the ratio of total roughened surface area to vertically projected area is not less than 1.5, indicating that both the two screening methods are accurate, and can be employed separately for screening high brightness light emitting diode. 
         [0093]    Although specific embodiments have been described above in detail, the description is merely for purposes of illustration. It should be appreciated, therefore, that many aspects described above are not intended as required or essential elements unless explicitly stated otherwise. Various modifications of, and equivalent acts corresponding to, the disclosed aspects of the exemplary embodiments, in addition to those described above, can be made by a person of ordinary skill in the art, having the benefit of the present disclosure, without departing from the spirit and scope of the disclosure defined in the following claims, the scope of which is to be accorded the broadest interpretation so as to encompass such modifications and equivalent structures.