Abstract:
A light-emitting diode (LED) for plant illumination includes a substrate, and a PN-junction light-emitting portion over the substrate. The light-emitting portion has a strained light-emitting layer with a component formula of Ga X In (1-X) As Y P (1-Y)  (0&lt;X&lt;1 and 0&lt;Y&lt;1), and a barrier layer, forming a 2˜40-pair alternating-layer structure with the strained light-emitting layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to Chinese Patent Application No. 201610757136.6 filed on Aug. 30, 2016, and is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 14/415,037 filed on Jan. 15, 2015, which in turn is a national stage application of, and claims priority to, PCT/CN2013/075684 filed on May 16, 2013, which claims priority to Chinese Patent Application No. 201310072627.3 filed on Mar. 7, 2013. The disclosures of these applications are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    In recent years, many studies have been made on plant cultivation via artificial light source. In particular, the plant cultivation by the light-emitting diode (LED) attracts much attention due to excellent monochromaticity, energy saving, long service life and small size. 
         [0003]    Plant illumination mainly includes the plant growth light and aquarium light. The plant growth light supplements the light source when the natural light is insufficient, which complements the sunlight and adjusts the agricultural product growth. The aquarium light not only improves the growth of aquatic plants, but also has the lighting effect for sightseeing. 
         [0004]    Compared with traditional plant illumination, the LED plant illumination is advantageous in the following aspects: i) energy saving. The LED plant illumination may directly generate the light for plant with same-lumen photon, which consumes little power; ii) high efficiency. As monochromatic light, the LED can generate light waves matching the plant requirement, which cannot be achieved by traditional plant light; iii) the LED plant illumination has rich wavelength types capable of controlling the plant flowering, fruiting, plant height and nutrient contents. With the further improvement of LED plant illumination technology, it will be used for multi-layer 3D combined cultivation systems with less system heat, small space and low thermal load. 
       SUMMARY 
       [0005]    The present disclosure describes an LED for plant illumination, including a new light-emitting material Ga X In (1-X) As Y P (1-Y)  of which can significantly improve the light-emitting efficiency by 50%-100%. 
         [0006]    An LED for plant illumination, comprising a substrate arranged at the PN junction light-emitting part of the substrate. The light-emitting part has a strained light-emitting layer with component formula of Ga X In (1-X) As Y P (1-Y)  (0&lt;X&lt;1 and 0&lt;Y&lt;1). 
         [0007]    In some embodiments, the light-emitting part has a strained light-emitting layer with component formula of Ga X In (1-X) As Y P (1-Y)  (0&lt;X&lt;1 and 0&lt;Y&lt;0.2). 
         [0008]    In some embodiments, the light-emitting part has a strained light-emitting layer with component formula of Ga X In (1-X) As Y P (1-Y)  (0&lt;X&lt;1 and 0&lt;Y&lt;0.1). 
         [0009]    In some embodiments, the light-emitting part has a strained light-emitting layer with component formula of Ga X In (1-X) As Y P (1-Y)  (0&lt;X&lt;1 and 0&lt;Y&lt;0.05). 
         [0010]    In some embodiments, the light-emitting part has a barrier layer, forming a 2˜40-pair alternating-layer structure with the strained light-emitting layer. 
         [0011]    In some embodiments, each alternating-layer structure is 5-100 nm thick. 
         [0012]    In some embodiments, the barrier layer has a component formula of (Al A Ga 1-A ) B In (1-B) P (0.3≦A≦1 and 0&lt;B&lt;1). 
         [0013]    In some embodiments, the substrate material may be GaAs, GaP or any one of their combinations. 
         [0014]    In some embodiments, the invention also comprises a buffer layer between the substrate and the light-emitting part. 
         [0015]    In some embodiments, the invention also comprises a window layer arranged on the light-emitting part. 
         [0016]    In some embodiments, the window layer material is GaP. 
         [0017]    In some embodiments, the window layer is 0.5-15 μm thick. 
         [0018]    In some embodiments, in the LED for improving photosynthesis during plant cultivation, the peak light-emitting wavelength of the strained light-emitting layer is 650 nm-750 nm. 
         [0019]    In some embodiments, in the LED for improving photosynthesis during plant cultivation, the peak light-emitting wavelength of the strained light-emitting layer is 700 nm-750 nm. 
         [0020]    In another aspect, an LED is provided for plant illumination, including a light-emitting part of strained light-emitting layer on the substrate with component formula of Ga X In (1-X) As Y P (1-Y)  (0&lt;X&lt;1 and 0&lt;Y&lt;1). The strained light-emitting layer material is GaInAsP, which can improve the light-emitting efficiency of the strained light-emitting layer. In addition, the material is helpful for improving life stability due to the lack of Al component. 
         [0021]    In addition, by adjusting the composition and thickness of the strained light-emitting layer, the light-emitting wavelength from the strained light-emitting layer is in a range of 650 nm-750 nm. In some embodiments, a window layer is provided at the light-emitting part of the LED for plant illumination, which is transparent to the light-emitting wavelength, and therefore will not absorb the light from the light-emitting part. In addition, it can have a current spreading function. 
         [0022]    Hence, according to some embodiments of this disclosure, a high output power and/or highly efficient LED capable of generating a large quantity of light-emitting wavelength of 650 nm-750 nm is provided. 
         [0023]    In another aspect, an epitaxial wafer for a plant lighting LED is provided, including from up to bottom: a growth substrate, a first red-light epitaxial laminated layer, a DBR semiconductor laminated layer and a second red-light epitaxial laminated layer, wherein, the first red-light epitaxial laminated layer comprises a first N-type ohmic contact layer, a first N-type covering layer, a first light-emitting layer, a first P-type covering layer and a first P-type ohmic contact layer; and the second red-light epitaxial laminated layer comprises a second N-type ohmic contact layer, a second N-type covering layer, a second light-emitting layer, a second P-type covering layer and a second P-type ohmic contact layer. 
         [0024]    In some embodiments, a doping concentration of the DBR semiconductor laminated layer is ≦5×10 17 , to form a high resistance interface. 
         [0025]    In some embodiments, light emitting wavelength of the first light-emitting layer is 710 nm˜750 nm, and that of the second light-emitting layer is 640 nm˜680 nm. 
         [0026]    In some embodiments, light emitting wavelength of the first light-emitting layer is 730 nm, and that of the second light-emitting layer is 660 nm. 
         [0027]    In some embodiments, an etching stop layer is provided between the DBR semiconductor laminated layer and the second red-light epitaxial laminated layer. 
         [0028]    In another aspect, an LED chip for a plant lighting LED is provided, including from up to bottom: a first red-light epitaxial laminated layer, a DBR semiconductor laminated layer, a second red-light epitaxial laminated layer and a conductive bonding substrate; in which, the first red-light epitaxial laminated layer comprises a first N-type ohmic contact layer, a first N-type covering layer, a first light-emitting layer, a first P-type covering layer and a first P-type ohmic contact layer; and the second red-light epitaxial laminated layer comprises a second N-type ohmic contact layer, a second N-type covering layer, a second light-emitting layer, a second P-type covering layer and a second P-type ohmic contact layer; wherein, light-emitting area of the first red-light epitaxial laminated layer is less than that of the second red-light epitaxial laminated layer; the first N-type ohmic contact layer is provided with a first electrode; between the first P-type ohmic contact layer and the second N-type ohmic contact layer is provided with an electronic-connected structure, and the second P-type ohmic contact layer is provided with a second electrode. 
         [0029]    In some embodiments, light emitting wavelength of the first light-emitting layer is 710 nm˜750 nm, and that of the second light-emitting layer is 640˜680 nm. 
         [0030]    In some embodiments, doping concentration of the DBR semiconductor laminated layer is ≦5×10 17 , to form a high resistance interface. 
         [0031]    In some embodiments, surface of the second red-light epitaxial laminated layer is preset with a light-emitting zone and a non-light-emitting zone, and a DBR semiconductor laminated layer is formed on the non-light-emitting zone of the second red-light epitaxial laminated layer. 
         [0032]    In some embodiments, area of the DBR semiconductor laminated layer is less than the light-emitting area of the second red-light epitaxial laminated layer, but larger than that of the first red-light epitaxial laminated layer. 
         [0033]    In some embodiments, the non-light-emitting zone on the surface of the second N-type ohmic contact layer is provided with an electric diffusion structure. 
         [0034]    In some embodiments, an etching stop layer is provided between the DBR semiconductor laminated layer and the second red-light epitaxial laminated layer. 
         [0035]    In another aspect, a light-emitting system is provided for plant lighting. The system can include a plurality of the LED chips described above. The LED chips can form an array over a packaging frame. 
         [0036]    In another aspect, a fabrication method for growing a plant lighting LED chip is provided, including: 1) epitaxial growth: provide a growth substrate, and form any of aforesaid LED epitaxial wafer for plant lighting; 2) substrate transfer: bond a conductive bonding substrate on the epitaxial wafer surface and remove the growth substrate to expose the first N-type ohmic contact layer surface of the epitaxial wafer; 3) defining of light-emitting zone: define a first light-emitting zone and a second light-emitting zone on the epitaxial wafer surface, and remove the first N-type ohmic contact layer, the first N-type covering layer, the first light-emitting layer and the first P-type covering layer of the second light-emitting zone to expose the first P-type ohmic contact layer; 4) electrode fabrication: remove the DBR semiconductor laminated layer of the second light-emitting zone and expose the surface of the second N-type ohmic contact layer; fabricate an N-type electrode on the surface of the first N-type ohmic contact layer, and fabricate an electronic-connected structure; electrically connect the first P-type ohmic contact layer and the second N-type ohmic contact layer. 
         [0037]    In some embodiments, in step 3), the epitaxial wafer surface is also defined with an isolation zone between the first light-emitting zone and the second light-emitting zone. 
         [0038]    In some embodiments, in step 3), remove the second light-emitting zone and the first N-type ohmic contact layer, the first N-type covering layer, the first light-emitting layer and the first P-type covering layer of the isolation zone. 
         [0039]    In some embodiments, after step 4), the DBR layer is larger than the first light-emitting zone but smaller than the second light-emitting zone. 
         [0040]    Other features and advantages of the present disclosure will be described in detail in the following specification, and moreover, will become obvious partially through the Specification or understood through implementations of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]    The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, together with the embodiments, are therefore to be considered in all respects as illustrative and not restrictive. In addition, the drawings are merely illustrative, which are not drawn to scale. 
           [0042]      FIG. 1  is a sectional structure diagram of an LED for plant illumination according to some embodiments. 
           [0043]      FIG. 2  is a side sectional view of a LED chip for plant lighting in accordance with Embodiment 7. 
           [0044]      FIG. 3  is a top view of the LED chip as shown in  FIG. 2 . 
           [0045]      FIG. 4  illustrates a first step of fabricating an LED chip for plant lighting according to some embodiments. 
           [0046]      FIG. 5  illustrates a second step of fabricating an LED chip for plant lighting according to some embodiments. 
           [0047]      FIG. 6  illustrates a third step of fabricating an LED chip for plant lighting according to some embodiments. 
           [0048]      FIG. 7  illustrates a fourth step of fabricating an LED chip for plant lighting according to some embodiments. 
           [0049]      FIG. 8  illustrates a fifth step of fabricating an LED chip for plant lighting according to some embodiments. 
           [0050]      FIG. 9  illustrates a sixth step of fabricating an LED chip for plant lighting according to some embodiments. 
           [0051]      FIG. 10  illustrates a seventh step of fabricating an LED chip for plant lighting according to some embodiments. 
           [0052]      FIG. 11  illustrates an eight step of fabricating an LED chip for plant lighting according to some embodiments. 
           [0053]      FIG. 12  illustrates a ninth step of fabricating an LED chip for plant lighting according to some embodiments. 
           [0054]      FIG. 13  illustrates a tenth step of fabricating an LED chip for plant lighting according to some embodiments. 
       
    
    
       [0055]    In the drawings:
         200 : growth substrate;  210 : far red-light epitaxial laminated layer;  211 : first N-type etching stop layer;  212 : first N-type ohmic contact layer;  213 : first N-type electrode diffusion layer;  214 : first N-type covering layer;  215 : first light-emitting layer;  216 : first P-type covering layer;  217 : first P-type ohmic contact layer;  220 : DBR semiconductor laminated layer;  230 : super red-light epitaxial laminated layer;  231 : second N-type etching stop layer;  232 : second N-type ohmic contact layer,  233 : second N-type electrode diffusion layer;  234 : second N-type covering layer;  235 : second light-emitting layer;  236 : second P-type covering layer;  237 : P-type transition layer;  238 : second P-type ohmic contact layer;  240 : mirror structure;  250 : conductive bonding layer;  260 : conductive bonding substrate;  271 : N-type electrode;  272 : BeAu metal layer;  273 : electronic-connected structure;  274 : electrode extension bar;  275 : P-type electrode.       
 
       DETAILED DESCRIPTION 
       [0057]    Based on study results so far, the light-emitting wavelength of light sources suitable for plant growth is near 450 nm (blue light) and 600-750 nm (red light). 
         [0058]    The traditional light-emitting layer for plant illumination is AlGaAsP or AlGaAs. However, the LED with light-emitting layer made of AlGaAsP or AlGaAs has low light-emitting output power. To promote feasible light source of LED for plant cultivation, it is necessary to develop LED with high output power and/or high efficiency in consideration of energy and cost saving. 
         [0059]    The following embodiments provide a LED with 650-750 nm wavelength suitable for plant illumination, featured by high output power and stable service life. 
         [0060]    The GaInP light-emitting wavelength is near 640 nm and the GaAs light-emitting wavelength is near 850 nm. In the following embodiments, the light-emitting layer GaInP material is doped with As and the thickness and strain capacity of the strained light-emitting layer are adjusted; therefore, an LED composed of new epitaxial structure for plant illumination is developed that is suitable for wavelength of 650-750 nm. 
         [0061]    Detailed descriptions will be given below about this disclosure with reference to accompanying drawings and embodiments. 
       Embodiment 1 
       [0062]    As shown in  FIG. 1 , an LED comprises: a substrate  11 , divided into a first surface and a second surface; a light-emitting part, which consists of a stack of semiconductor material layers, including a buffer layer  12 , a first restriction layer  13 , a light-emitting layer  14  and a second restriction layer  15 , sequentially from down up and formed on the first surface of the substrate  11 ; a window layer  16  formed on a partial region of the second restriction layer  15  of the light-emitting part; a second electrode  17 , formed on the window layer  16 ; and a second electrode  18 , formed on the second surface of the substrate  11 . 
         [0063]    In the element, the substrate  11  material may be GaAs, GaP or any one of their combinations. 
         [0064]    The buffer layer  12  can mitigate lattice imperfection of the epitaxially growing substrate but is not a necessary film for the element. 
         [0065]    The light-emitting part consists of an alternating layer (of strained light-emitting layer and barrier layer) structure, including at least two 2 pairs (preferably 2-40 pairs). The structure of each pair of alternating-layers is, without limitation to, 5-100 nm thick. A structure of a plurality of alternating layers can effectively improve the saturation current of the element. In this embodiment, the pair number of the alternating layer structure of alternating strained light-emitting layer and barrier layer is 6. The structure of each pair is 40 nm thick and the total thickness is 240 nm. 
         [0066]    The strained light-emitting layer material is Al-free GaInAsP with component formula of Ga X In (1-X) As Y P (1-Y)  (0&lt;X&lt;1 and 0&lt;Y&lt;1). In some embodiments, to better control the peak wave of the light-emitting layer within 650 nm-750 nm, the Y value is preferably 0&lt;Y&lt;0.2. In this embodiment, X=0.5 and Y=0.01. 
         [0067]    The barrier layer material is AlGaInP with component formula of (Al A Ga 1-A ) B In (1-B) P (0.3≦A≦1 and 0&lt;B&lt;1). In this embodiment, A=0.5 and B=0.5. 
         [0068]    The window layer is GaP (thickness: 0.5 μm-15 μm) and is capable of current expansion. The window layer is not a necessary film for the element, which can be chosen based on the process parameters. 
         [0069]    Referring to Table 1 for the optical-electrical characteristics of the 42×42 mil large-power quaternary LED element structure. As shown in Table 1, based on the flowing current results of the first electrode and second electrode after being powered on, the element emits red light with an average peak wavelength of 685.6 nm. When the 350 mA current flows through in forward direction, the average forward voltage value is 2.25 V and the output power is 250.3 mW. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 VF/V 
                 Po/mW 
                 WLD/nm 
                 WLP/nm 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 No. 1 
                 2.26 
                 248.5 
                 656.2 
                 686.0 
               
               
                   
                 No. 2 
                 2.23 
                 252.1 
                 656.2 
                 685.1 
               
               
                   
                 Average 
                 2.25 
                 250.3 
                 656.2 
                 685.6 
               
               
                   
                   
               
             
          
         
       
     
       Embodiment 2 
       [0070]    In comparison with Embodiment 1, t the following is the same: in the 42.times.42 mil quaternary LED element structure of this embodiment, the pair number of the alternating-layer (of strained light-emitting layer and barrier layer) structure is 6. The structure of each pair is 60 nm thick and the total thickness is 360 nm. The difference is that: the strained light-emitting layer is Ga X In (1-X) As Y P (1-Y)  (X=0.5 and Y=0.025). Based on the flowing current results of the first electrode and second electrode after being powered on, the element emits red light with average main wavelength of 680.2 nm and average peak wavelength of 714.9 nm. When the 350 mA current flows through in forward direction, the average forward voltage value is 2.22 V and the output power is 232.7 mW. 
       Embodiment 3 
       [0071]    In comparison with Embodiment 1, the difference is that: the strained light-emitting layer of the 42.times.42 mil quaternary LED element structure of this embodiment is Ga X In (1-X) As Y P (1-Y)  (X=0.5 and Y=0.04). 
         [0072]    Refer to Table 2 for the optical-electrical characteristics of the 42.times.42 mil quaternary LED element structure. As shown in Table 2, based on the flowing current results of the first electrode and second electrode after being powered on, the element emits red light with average peak wavelength of 722.0 nm. When the 350 mA current flows through in forward direction, the average forward voltage value is 2.18 V and the output power is 216.5 mW. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 VF/V 
                 Po/mW 
                 WLD/nm 
                 WLP/nm 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 No. 1 
                 2.19 
                 215.7 
                 693.7 
                 721.7 
               
               
                   
                 No. 2 
                 2.20 
                 222.7 
                 697.4 
                 723.5 
               
               
                   
                 No. 3 
                 2.16 
                 220.1 
                 701.7 
                 723.5 
               
               
                   
                 No. 4 
                 2.19 
                 207.6 
                 691.5 
                 719.3 
               
               
                   
                 Average 
                 2.19 
                 216.5 
                 696.1 
                 722.0. 
               
               
                   
                   
               
             
          
         
       
     
       Embodiment 4 
       [0073]    In comparison with Embodiment 3, the difference is that: the strained light-emitting layer of the 42.times.42 mil quaternary LED element structure of this embodiment is Ga X In (1-X) As Y P (1-Y)  (X=0.5 and Y=0.05). Based on the flowing current results of the first electrode and second electrode after powering on, the element emits red light with average main wavelength of 712.3 nm and average peak wavelength of 739.5 nm. When the 350 mA current flows through in forward direction, the average forward voltage value is 2.21 V and the output power is 202.2 mW. 
       Embodiment 5 
       [0074]    In comparison with Embodiment 3, the difference is that: in the 42.times.42 mil quaternary LED element structure of this embodiment, the pair number of alternating-layer (of strained light-emitting layer and barrier layer) structure is 9. The structure of each pair is 50 nm thick and the total thickness is 450 nm. Based on the flowing current results of the first electrode and second electrode after powering on, the element emits red light with average main wavelength of 701.5 nm and average peak wavelength of 733.5 nm. The saturation current is above 2,000 mA. When the 350 mA current flows through in forward direction, the average forward voltage value is 2.24 V and the output power is 223.9 mW. 
         [0075]    To sum up, in the LED element structure for improving photosynthesis during plant cultivation, the peak light-emitting wavelength can be controlled within 650-750 nm by adjusting the composition of strained light-emitting layer, component value range and the pair number and thickness range of the alternating-layer (of strained light-emitting layer and barrier layer) structure, thereby achieving high output power. In addition, the material is helpful for improving life stability due to the lack of Al component. 
       Embodiment 6 
       [0076]    The larger is Y value in the strain light-emitting layer Ga X In (1-X) As Y P (1-Y) , the narrower is the material gap, and the longer is the light emitting wavelength. Moreover, mismatch degree between the light emitting portion and base gets larger, and lattice growth quality of material gets poorer. As evidenced by experiment, as Y changes from 0 to 0.1, mismatch degree of the light emitting portion material increases gradually and lattice growth quality gets poorer. As the comparison examples No. 1˜No. 8 in Table 3 shown, when b value of the barrier layer (Al A Ga 1-A ) B In (1-B) P and total thickness of the alternating laminated structure in light emitting portion (MQW structure) remain unchanged, if Y is 0.01, light emitting efficiency is highest. 
         [0077]    With As added in the light emitting layer, lattice constant of the strain light-emitting layer in the light-emitting zone is larger than that of GaAs, thus generating compression strain. Therefore, to reduce such compression strain, a barrier layer (Al A Ga 1-A ) B In (1-B) P is designed, wherein, 0.5&lt;B≦0.52, i.e., lattice constant of the barrier layer is less than that of the GaAs base, thus generating tension strain. With a combination of the light-emitting zone and the barrier layer, effect and substrate mismatch degree get smaller to improve light-emitting efficiency and reliability of the material. As shown in Table 3, when B is 0.52, the light-emitting efficiency is highest. 
         [0078]    For a MQW structure, total tension strain=compression strain of strain light-emitting layer (quantum well)*well thickness (positive)+tension strain of barrier layer (quantum barrier)*barrier thickness (negative). Total tension strain is preferred to be less than 500 ppm and preferably 100˜200 ppm as evidenced by an experiment. To achieve high-lighting efficiency LED with 650˜750 nm light-emitting wavelength, as shown in optimized experiment results, when B=0.52 in the barrier layer (Al A Ga 1-A ) B In (1-B) P and Y=0.01 in the light-emitting layer Ga X In (1-X) As X P (1-Y) , and total thickness is 360 nm, light-emitting effect of LED is best, reaching 1.5˜2 times compared with conventional method. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                   
                 No. 
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
               
               
                   
               
             
          
           
               
                 Y value 
                 0 
                 0.01 
                 0.025 
                 0.01 
                 0.01 
                 0.01 
                 0.01 
                 0.01 
               
               
                 [Light emitting 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 layer  
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Ga x In( 1−x )AS y P( 1−y )] 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 b value 
                 05 
                 0.5 
                 0.5 
                 0.5 
                 0.52 
                 0.53 
                 0.52 
                 0.52 
               
               
                 [Barrier layer 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 (Al A Ga 1−A ) B In( 1−B )P] 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Total thickness 
                 240 
                 240 
                 240 
                 240 
                 240 
                 240 
                 360 
                 450 
               
               
                 of MQW/nm 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 (Po/VF/350 mA) 
                 13.70% 
                 28.80% 
                 27.90% 
                 28.40% 
                 29.10% 
                 28.30% 
                 30.50% 
                 27% 
               
               
                 Light-emitting 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 efficiency 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 (Po/VF/350 mA) 
               
               
                   
               
             
          
         
       
     
       Embodiment 7 
       [0079]    It is common to pack the deep-blue-light, ultra-red-light and far-red-light LED chip with single wavelength one by one, and assemble individual packages on the light plate in various arrangements, as shown in  FIG. 14 . Due to limited space and cost, it is better to use less LEDs in smaller size. 
         [0080]    This embodiment discloses a LED for plant lighting, in which, ultra-red light (˜660 nm) and far-red light (˜730 nm) for plant lighting are realized in a single chip via laminated layer epitaxy. 
         [0081]    With reference to  FIG. 2 , a vertical LED chip according to the present invention is provided, comprising: a far-red-light epitaxial laminated layer  210 , a DBR semiconductor laminated layer  220 , a ultra-red-light epitaxial laminated layer  230 , a mirror structure  240 , a conductive bonding layer  250 , a conductive substrate  260 , an N-type electrode  271  and a P-type electrode  275 , 
         [0082]    Wherein, light-emitting wavelength of the far-red-light epitaxial laminated layer  210  is 710 nm˜750 nm, preferably, ˜730 nm, and that of the far-red-light epitaxial laminated layer  210  is 640 nm˜680 nm, preferably, ˜660 nm. In some embodiments, lighting area  210   a  of the far-red-light epitaxial laminated layer  210  is less than or equals to lighting area  230   a  of the ultra-red-light epitaxial laminated layer  230 . Preferably, lighting area  210   a  of the far-red-light epitaxial laminated layer  210  is one-third of lighting area  230   a  of the ultra-red-light epitaxial laminated layer  230 . 
         [0083]    The DBR semiconductor laminated layer  220  is located between the far-red-light epitaxial laminated layer  210  and the ultra-red-light epitaxial laminated layer  230 . On the one hand, it reflects far red light emitted by the far-red-light epitaxial laminated layer  210  and prevents such light from being absorbed by the ultra-red-light epitaxial laminated layer  230 ; on the other hand, a high-resistance interface is formed as a current blocking layer to make current flow to the light-emitting zone of the ultra-red-light epitaxial laminated layer  230 , which has no far-red-light epitaxial laminated layer  210 , so as to improve luminance. Therefore, doping concentration of the DBR semiconductor laminated layer  220  is preferred to be not more than 5×10 17 , and preferably 4.00×10 17 . 
         [0084]    The far-red-light epitaxial laminated layer  210  and the ultra-red-light epitaxial laminated layer  230  can be made of AlGaInP-based material, wherein, the far-red-light epitaxial laminated layer  210 , from up to bottom, comprises an N-type ohmic contact layer  212 , a first N-type electrode diffusion layer  213 , a first N-type covering layer  214 , a first light emitting layer  215 , a first P-type covering layer  216  and a first P-type ohmic contact layer  217 ; and the ultra-red-light epitaxial laminated layer  230 , from up to bottom. comprises a second N-type ohmic contact layer  232 , a second N-type electrode diffusion layer  233 , a second N-type covering layer  234 , a second light emitting layer  235 , a second P-type covering layer  236 , a P-type transition layer  237  and a second P-type ohmic contact layer  238 . An N-type etching stop layer  231  can be provided between the ultra-red-light epitaxial laminated layer  230  and the DBR semiconductor laminated layer  220 . 
         [0085]    A step-shaped structure is provided between the far-red-light epitaxial laminated layer  210  and the ultra-red-light epitaxial laminated layer  230  for fabricating an electronic-connected structure  271 , wherein, one end is connected to the ohmic contact layer  261  of the far-red-light epitaxial laminated layer  210 , and the other end is connected to the ohmic contact layer  237  of the ultra-red-light epitaxial laminated layer  230 . Preferably, as lighting area  230   a  of the ultra-red-light epitaxial laminated layer  230  is larger than lighting area  210   a  of the far-red-light epitaxial laminated layer  210 , an extension bar  274  can be set on the ohmic contact layer  237  of the ultra-red-light epitaxial laminated layer  230  to ensure even light-emitting of the light emitting layer, as shown in  FIG. 3 . 
         [0086]    With reference to  FIGS. 4-13  and fabrication method, the structure of the LED chip is described in detail below, mainly comprising: (I) epitaxial growth; (II) substrate transfer; (III) defining of light-emitting zone; (IV) electrode fabrication. 
         [0087]    (I) Epitaxial Growth 
         [0088]    Form an epitaxial structure on the growth substrate, as shown in  FIG. 4 . The key of the structure is to grow an epitaxial layer as shown in Table 4 on the GaAs substrate in sequence. It should be noted that only one typical material is listed in the table below for material of each layer of the epitaxial structure. The material in actual application is not limited to the listed one but can be expended to any other necessary materials. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 GaAs substrate 
               
             
          
           
               
                   
                   
                   
                 Thickness 
                 Doping 
               
               
                 Function 
                 Layer 
                 Material 
                 (nm) 
                 concentration 
               
               
                   
               
               
                 P-type ohmic 
                 P-GaP 
                 GaP:Mg 
                 ≧500 
                 ≧8.00 × 10 17   
               
               
                 contact layer (2) 
               
               
                 P-type transition 
                 P-AlGaInP 
                 AlGaInP:Mg 
                 ≦100 
                 ≧2.00 × 10 18   
               
               
                 layer 
               
               
                 P-type covering 
                 P-AlInP(2) 
                 AlInP:Mg 
                 ≧500 
                 ≧1.20 × 10 18   
               
               
                 layer (2) 
               
               
                 ~660 nm light 
                 GaInP-well 
                 GaInP 
                 ≧8 × 3 
                 — 
               
               
                 emitting layer 
                 AlGaInP-barrier 
                 AlGaInP 
                 ≧8 × 3 
                 — 
               
               
                 N-type covering 
                 N-AlInP(2) 
                 AlInP:Si 
                 ≧500 
                 ≧1.60 × 10 18   
               
               
                 layer (2) 
               
               
                 N-type current 
                 N-AlGaInP(2) 
                 AlGaInP:Si 
                 ≧1000  
                 ≧1.00 × 10 17   
               
               
                 diffusion layer (2) 
               
               
                 N-type ohmic 
                 N-GaAs(2) 
                 GaAs:Si 
                 ≧100 
                 ≧6.00 × 10 18   
               
               
                 contact layer (2) 
               
               
                 N-type etching 
                 N-GaInP(2) 
                 GaInP:Si 
                 ≧100 
                 ≧1.00 × 10 18   
               
               
                 stop layer (2) 
               
               
                 DBR semiconductor 
                 P-AlAs 
                 AlAs:Mg 
                 ≧54.5 × 2   
                 ≦5.00 × 10 17   
               
               
                 laminated layer 
                 P-AlGaAs 
                 AlGaAs:Mg 
                 ≧50.9 nm × 2 
                 ≦5.00 × 10 17   
               
               
                 P-type ohmic 
                 P-GaAs 
                 GaAs:Mg 
                 ≧500 
                 ≧1.00 × 10 18   
               
               
                 contact layer (1) 
               
               
                 P-type covering 
                 P-AlInP(1) 
                 AlInP:Mg 
                 ≧900 
                 ≧1.20 × 10 18   
               
               
                 layer (1) 
               
               
                 ~730 nm light 
                 AlGaAs-well 
                 AlGaAs 
                 ≧12 × 3  
                 — 
               
               
                 emitting layer (1) 
                 AlGaInP-barrier 
                 AlGaInP 
                 ≧13 × 3  
                 — 
               
               
                 N-type covering 
                 N-AlInP(1) 
                 AlInP:Si 
                 ≧500 
                 ≧1.60 × 10 18   
               
               
                 layer (1) 
               
               
                 N-type current 
                 N-AlGaInP(1) 
                 AlGaInP:Si 
                 ≧1000  
                 ≧1.00 × 10 17   
               
               
                 diffusion layer (1) 
               
               
                 N-type ohmic 
                 N-GaAs(1) 
                 GaAs:Si 
                 ≧100 
                 ≧6.00 × 10 18   
               
               
                 contact layer (1) 
               
               
                 N-type etching 
                 N-GaInP(1) 
                 GaInP:Si 
                 ≧100 
                 ≧1.00 × 10 18   
               
               
                 stop layer(1) 
               
               
                   
               
             
          
         
       
     
         [0089]    (II) Substrate Transfer 
         [0090]    In this step, bond the conductive substrate  260  and remove the growth substrate. To reach sufficient light emitting efficiency, a mirror structure is designed between the conductive substrate  260  and the epitaxial structure. In the embodiments below, at first, fabricate a mirror structure before substrate transfer. Details are as follows. 
         [0091]    At first, on the surface of the second P-type ohmic contact layer  238  of the epitaxial structure, plate a light-transmission dielectric layer, and make a hole on the dielectric layer to remove the plated P-type metal ohmic contact layer (such as AuZn) and metal mirror layer (such as Au) to form a mirror structure  240 . According to a variant, deposit a transparent conducing layer (such as ITO) and a metal mirror layer (such as Ag) on the surface of the second P-type ohmic contact layer  238  in sequence to form another mirror structure. 
         [0092]    Next, plate a bonding layer  250  on the mirror structure  240 , and perform bonding for the conductive substrate  260  with a bonding layer to complete metal bonding. The structure is shown in  FIG. 5 . The metal bonding layer  250  can be made of Au/Au, Au/In, Au/Sn, Ni/Sn. 
         [0093]    Remove GaAs substrate with alkaline solution and the first N-type etching stop layer  211  with hydrochloride acid solution and expose the first N-type ohmic contact layer  212  to complete substrate transfer, as shown in  FIG. 6 . 
         [0094]    (III) Defining of Light-Emitting Zone 
         [0095]    Preset a far-red-light light-emitting zone  210   a  on surface of the first N-type ohmic contact layer  212  of the epitaxial structure, and remove the first N-type ohmic contact layer  212 , the first N-type current diffusion layer  213 , the first N-type covering layer  214 , the first light emitting layer  215 , the first P-type covering layer  216  of the far-red-light light-emitting zone  210  to expose the first P-type ohmic contact layer  217 , as shown in  FIG. 7 . The far-red-light light-emitting zone  210   a  can be referred to  FIG. 3 . 
         [0096]    (IV) Electrode Fabrication 
         [0097]    At first, fabricate a BeAu metal layer  272  on surface of the first P-type ohmic contact layer  217 , and form ohmic contact with the first P-type ohmic contact layer  217  after annealing, as shown in  FIG. 8 . 
         [0098]    Next, preset a ultra-red-light light-emitting zone  230   a  on surface of the first P-type ohmic contact layer  217  and remove the first P-type ohmic contact layer  217 , the DBR semiconductor laminated layer  220  and the second N-type etching stop layer  231  of ultra-red-light light-emitting zone  230   a  to expose the second N-type ohmic contact layer  232 , as shown in  FIG. 9 . Remove the first P-type ohmic contact layer  217  and the DBR semiconductor laminated layer  220  with phosphoric acid solution, and remove the second N-type etching stop layer  231  with hydrochloride acid solution. 
         [0099]    Remove the second N-type ohmic contact layer  232  with LIT Litho or phosphoric acid solution and leave the ohmic contact zone for patterning, as shown in  FIG. 10 . The remaining portion can be referred to corresponding areas of the electronic-connected structure  273  and the electrode extension bar  274  as shown in  FIG. 3 . 
         [0100]    Next, evaporate GeAu on the first N-type ohmic contact layer  212  as the N-type electrode  271 , and form GeAu metal on the second N-type ohmic contact layer  232 , and connect it to the BeAu metal layer  272  on surface of the first P-type ohmic contact layer  217  as an electronic-connected structure  273  and an electrode extension bar  274 . Form ohmic contact after annealing, as shown in  FIG. 11 . 
         [0101]    Next, singularize the chip and remove part of the second N-type electrode diffusion layer  233 , the second N-type covering layer  234 , the second light emitting layer  235 , the second P-type covering layer  236  and the P-type transition layer  237 , till the second P-type ohmic contact layer  238  for patterning, as shown in  FIG. 12 . 
         [0102]    In some embodiments, form a light-intensifying structure on surfaces of the first N-type electrode diffusion layer  213  and the second N-type electrode diffusion layer  233  with hydrochloride acid solution, as shown in  FIG. 13 . 
         [0103]    Last, form a P-type electrode  275  on back of the conductive substrate  260  to complete a vertical LED chip for plant lighting. 
         [0104]    With a combination of epitaxial growth of ultra-red-light and far-red-light laminated layer and chip fabrication, this embodiment reduces number of packages and area of plant lighting plate, and therefore cut cost. 
         [0105]    All references referred to in the present disclosure are incorporated by reference in their entirety. 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.