Abstract:
A light-emitting element, comprises: a first active layer, generating a first light comprising a first dominant wavelength, wherein the first active layer comprises a first quantum well comprising a first quantum-well band gap and a second quantum well comprising a second quantum-well band gap, and the first quantum well and the second quantum well are alternately stacked to form the first active layer, wherein a difference between the first quantum-well band gap and the second quantum-well band gap is between 0.06eV and 0.1eV, and each of the first quantum-well and the second quantum-well is devoid of a barrier; and a second active layer on the first active layer, generating a second light comprising a second dominant wavelength; wherein a difference between the first dominant wavelength and the second dominant wavelength is 150nm to 220nm.

Description:
RELATED APPLICATION 
     This application claims the benefit of TW application Ser. No. 100124718, filed Jul. 12, 2011, entitled “A LIGHT-EMITTING ELEMENT WITH MULTIPLE LIGHT-EMITTING STACKED LAYERS”, the contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a light-emitting element, and more particularly, to a light-emitting element having multiple light-emitting stacked layers. 
     2. Description of the Related Art 
     Light-emitting Diode (LED) is a solid state semiconductor element comprising a p-n junction formed between a p-type semiconductor layer and an n-type semiconductor layer. When imposing a certain level of forward voltage to the p-n junction, holes from the p-type semiconductor layer and electrons from the n-type semiconductor layer are combined to release light. The region for light releasing is generally called light-emitting region. 
     The primary features of an LED include its small size, excellent CRI, high reliability, high efficiency, long life, and short initial illumination time. The LED has been applied widely to optical display devices, traffic signals, data storing devices, communication devices, illumination devices, and medical apparatuses. Along with the launch of the full-color LED, LED has gradually replaced traditional lighting apparatus such as fluorescent lights and incandescent lamps. 
     The price of the substrate occupies large proportion to the cost of manufacturing LED. Therefore, how to reduce the amount of utilizing substrate raises concern. 
     SUMMARY OF THE DISCLOSURE 
     A light-emitting element, comprises: a first active layer, generating a first light comprising a first dominant wavelength, wherein the first active layer comprises a first quantum well comprising a first quantum-well band gap and a second quantum well comprising a second quantum-well band gap, and the first quantum well and the second quantum well are alternately stacked to form the first active layer, wherein a difference between the first quantum-well band gap and the second quantum-well band gap is between 0.06eV and 0.1eV, and each of the first quantum-well and the second quantum-well is devoid of a barrier; and a second active layer on the first active layer, generating a second light comprising a second dominant wavelength; wherein a difference between the first dominant wavelength and the second dominant wavelength is 1.50nm to 220mn. 
     A light-emitting element, comprises: a first active layer, comprising a first band gap, wherein the first active layer comprises a first quantum well comprising a first quantum-well band gap and a second quantum well comprising a second quantum-well band gap, and the first quantum well and the second quantum well are alternately stacked to form the first active layer, wherein a difference between the first quantum-well band gap and the second quantum-well band gap is between 0.06eV and 0.1eV; and a second active layer on the first active layer, comprising a second band gap; wherein a difference between the first band gap and the second band gap is between 0.3eV and 0.5eV.
         A light-emitting element, comprises: a first active layer, generating an invisible light, wherein the first active layer comprises a first quantum well comprising a first quantum-well band gap and a second quantum well comprising a second quantum-well band gap, and the first quantum well and the second quantum well are alternately stacked to form the first active layer, wherein a difference between the first quantum-well band gap and the second quantum-well band gap is between 0.06eV and 0.1eV, and each of the first quantum-well and the second quantum-well is devoid of a barrier; and a second active layer on the first active layer, generating a visible light.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide easy understanding of the application, and are incorporated herein and constitute a part of this specification. The drawings illustrate embodiments of the application and, together with the description, serve to illustrate the principles of the application. 
         FIG. 1  illustrates a cross-sectional view of a light-emitting element in accordance with an embodiment of the present application. 
         FIG. 2  illustrates a cross-sectional view of a light-emitting element in accordance with another embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     To better and concisely explain the disclosure, the same name or the same reference number given or appeared in different paragraphs or figures along the specification should has the same or equivalent meanings while it is once defined anywhere of the disclosure. 
     The following shows the description of the embodiments of the present disclosure in accordance with the drawings. 
       FIG. 1  discloses a light-emitting element  1  including a substrate  10 ; a first light-emitting stacked layer  2  formed on the substrate  10 ; a tunneling layer  12  formed on the first light-emitting stacked layer  2 ; a second light-emitting stacked layer  3  formed on the tunneling layer  12 ; and a contact layer  14  formed on the second light-emitting stacked layer  3 . The first light-emitting stacked layer  2  includes a first semiconductor layer  22 , a first active layer  24 , and a second semiconductor layer  26  sequentially formed between the substrate  10  and the tunneling layer  12 . The second light-emitting stacked layer  3  includes a third semiconductor layer  32 , a second active layer  34 , and a forth semiconductor layer  36  sequentially formed between the contact layer  14  and the tunneling layer  12 . There is a light-emitting stacked layer formed on a substrate in a conventional light-emitting element. The light-emitting element  1  includes two light-emitting stacked layers on the substrate  10  in this embodiment. One of the advantages is that the light-emitting efficiency of the light-emitting element  1  is about the same as the sum of the light-emitting efficiency of two conventional light-emitting elements. Moreover, it can reduce the cost of manufacturing by reducing the amount of the substrate because the light-emitting element  1  only uses one substrate, comparing to the two conventional light-emitting element using two substrates. 
     The substrate  10  can be for growing and/or supporting the light-emitting stacked layers thereon. The material of the substrate  10  includes insulating material such as sapphire, diamond, glass, quartz, acryl, or AlN, or conductive material such as Cu, Al, diamond like carbon (DLC), SiC, metal matrix composite (MMC), ceramic matrix composite (CMC), Si, IP, GaAs, Ge, GaP, GaAsP, ZnSe, ZnO, InP, LiGaO 2 , or LiAlO 2 . The material of the substrate  10  for growing the light-emitting stacked layers, for example, can be sapphire, GaAs, or SiC. 
     The first light-emitting stacked layer  2  and/or the second light-emitting stacked layer  3  can be directly grown on the substrate  10 , or fixed on the substrate  10  by a bonding layer (not shown). The material of the first light-emitting stacked layer  2  and the second light-emitting stacked layer  3  includes a semiconductor material containing more than one element selected from a group consisting of Ga, Al, In, As, P, N, Zn, Cd, and Se. The polarities of the first semiconductor layer  22  and the second semiconductor layer  26  are different. The polarities of the third semiconductor layer  32  and the forth semiconductor layer  36  are different. The first active layer  24  and the second active layer  34  can emit light, wherein the first active layer  24  includes a first band gap and the second active layer  34  includes a second band gap. The first band gap and the second band gap are different in this embodiment. The difference between the first band gap and the second band gap is between 0.3 eV and 0.5 eV. The first band gap can be smaller or larger than the second band gap. The first band gap is 1.45 eV and the second band gap is 1.9 eV, for instance. In another embodiment, the light generated from the first active layer  24  is invisible to the eyes of humans. The wavelength of the invisible light is about smaller than 400 nm or larger than 780 nm. It can be better between 780 nm and 2500 nm or between 300 nm and 400 nm, preferably between 780 nm and 900 nm, in this embodiment. The light generated from the second active layer  34  is visible to the eyes of humans. The wavelength of the visible light is about between 400 nm and 780 nm, preferably between 560 nm and 750 nm, in this embodiment. In another embodiment, the light generated from the first active layer  24  includes a first dominant wavelength and the light generated from the second active layer  34  includes a second dominant wavelength, wherein the difference between the first dominant wavelength and the second dominant wavelength is about 150 nm to 220 nm, and the first dominant wavelength can be larger or smaller than the second dominant wavelength. This embodiment can be applied to medical treatment. One of the advantages is that a single light-emitting element can include different functions, for example, the first dominant wavelength of 815 nm can promote healing the wound, and the second dominant wavelength of 633 nm can eliminate wrinkles. 
     In another embodiment, a first quantum well  24   a  and a second quantum well  24   b  are stacked alternately to form the first active layer  24 . The first quantum well  24   a  incudes a first quantum-well band gap and the second quantum well  24   b  incudes a second quantum-well band gap, wherein the first quantum-well band gap is different from the second quantum-well band gap. The difference between the first quantum-well band gap and the second quantum-well band gap is about 0.06 eV to 0.1 eV, and the first quantum-well band gap can be smaller or larger than the second quantum-well band gap. A third quantum well  34   a  and a forth quantum well  34   b  are stacked alternately to form the second active layer  34 . The third quantum well  34   a  includes a third quantum-well band gap and the forth quantum well  34   b  incudes a forth quantum-well band gap, wherein the third quantum-well band gap is different from the forth quantum-well band gap. The difference between the third quantum-well band gap and the forth quantum-well band gap is about 0.06 eV to 0.1 eV, and the third quantum-well band gap can be smaller or larger than the forth quantum-well band gap. 
     The tunneling layer  12  is grown on the first light-emitting stacked layer  2 . The doping concentration of the tunneling layer  12  is larger than 8×10 18 /cm 3  so the electrons can pass it because of the tunneling effect. The material of the tunneling layer  12  includes semiconductor material containing more than one element selected from a group consisting of Ga, Al, In, As, P, N, Zn, Cd, and Se. In another embodiment, the tunneling layer  12  can be replaced by a first bonding layer to bond the first light-emitting stacked layer  2  to the second light-emitting stacked layer  3 . The material of the first bonding layer includes transparent conductive material such as ITO, InO, SnO, CTO, ATO, ZnO, MgO, AlGaAs, GaN, GaP, AZO, ZTO, GZO, IZO, or Ta 2 O 5 , or insulating material such as Su8, benzocyclobutene (BCB), perfluorocyclobutane (PFCB), epoxy, acrylic resin, cyclic olefin copolymers (COC), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyimide (PI), polycarbonate (PC), polyetherimide, fluorocarbon polymer, glass, Al 2 O 3 , SiO 2 , TiO 2 , SiN x , spin-on-glass (SOG), or tetraethoxysilane (TEOS). The contact layer  14  is for conducting current. The material of the contact layer  14  includes GaP, Al x Ga 1−x As(0≦x≦1), or Al a Ga b In 1−a−b P (0≦a≦1, 0≦b≦1, 0≦a+b≦1). 
     Referring to  FIG. 2 , a light-emitting device  4  includes a carrier  40 ; a second bonding layer  42  on the carrier  40 ; a first light-emitting structure  41  and a second light-emitting structure  43  on the second bonding layer  42 ; an insulating layer  44  on the second bonding layer  42 , the light-emitting structure  41  and the second light-emitting structure  43 , and an electrical-connecting structure  46  on the insulating layer  44  to electrically connect the light-emitting structure  41  and the second light-emitting structure  43 . The light-emitting structure  41  and the second light-emitting structure  43  are similar to the aforementioned light-emitting element  1 , and include the first light-emitting stacked layer  2 ; the tunneling layer  12 ; the second light-emitting stacked layer  3 , and the contact layer  14  on the second bonding layer  42 . The light-emitting structure  41  and the second light-emitting structure  43  respectively further include a first electrode  16  on the contact layer  14  and a second electrode  18  on the first light-emitting stacked layer  2 . The electrical-connecting structure  46  can electrically connect the second electrode  18  of the first light-emitting structure  41  with the first electrode  16  of the second light-emitting structure  43 . 
     The carrier  40  can be for growing and/or supporting the light-emitting structures thereon. The material of the carrier  40  includes insulating material such as sapphire, diamond, glass, quartz, acryl, ZnO, or AlN, or conductive material such as Cu, Al, diamond like carbon (DLC), SiC, metal matrix composite (MMC), ceramic matrix composite (CMC), Si, IP, ZnSe, GaAs, Ge, GaP, GaAsP, InP, LiGaO 2 , or LiAlO 2 . The material of the carrier  40  for growing light-emitting structures, for example, can be sapphire, GaAs, or SiC. 
     The second bonding layer  42  is for bonding the light-emitting structures and the carrier  40 . The material of the second bonding layer  42  can be transparent bonding material such as such as Sub, benzocyclobutene (BCB), perfluorocyclobutane (PFCB), epoxy, acrylic resin, cyclic olefin copolymers (COC), polyimide (PI), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polycarbonate (PC), polyetherimide, fluorocarbon polymer, glass, Al 2 O 3 , SiO 2 , TiO 2 , SiN x , spin-on-glass (SOG), or tetraethoxysilane (TEOS). The second bonding layer  42  can be insulating material to electrically insulate the first light-emitting structure  41  from the second light-emitting structure  43 . The second bonding layer  42  can be replaced by a buffer layer for growing the light-emitting structures in another embodiment. The material of the buffer layer includes Al x Ga 1−x As (0≦x≦1), Al a Ga b In 1−a−b P (0≦a≦1, 0≦b≦1, 0≦a+b≦1), or Al a Ga b In 1−a−b N(0≦a≦1, 0≦b≦1, 0≦a+b≦1). 
     The insulating layer  44  is for protecting and insulating the first light-emitting structure  41  from the second light-emitting structure  43 . The material of the insulating layer  44  can be insulating material such as such as Su8, benzocyclobutene (BCB), perfluorocyclobutane (PFCB), epoxy, acrylic resin, cyclic olefin copolymers (COC), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyimide (PI), polycarbonate (PC), polyetherimide, fluorocarbon polymer, glass, Al 2 O 3 , SiO 2 , TiO 2 , SiN x , spin-on-glass (SOG), or tetraethoxysilane (TEOS). The electrical-connecting structure  46  is for electrically connecting the first light-emitting structure  41  and the second light-emitting structure  43 . The material of the electrical-connecting structure  46  can be transparent conductive material such as ITO, InO, SnO, CTO, ATO, ZnO, MgO, AlGaAs, GaN, GaP, AZO, ZTO, GZO, IZO, or Ta 2 O 5 , or metal material such as Ge, Cu, Al, Mo, Cu—Sn, Cu—Zn, Cu—Cd, Ni—Sn, Ni—Co, or Au alloy. 
     It will be apparent to those having ordinary skill in the art that various modifications and variations can be made to the devices in accordance with the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure covers modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.