Abstract:
A light-emitting device is provided. The light-emitting device comprises: a semiconductor structure comprising a first type semiconductor layer, a second type semiconductor layer, and an active layer between the first type semiconductor layer and the second type semiconductor layer; and an isolation region through the second type semiconductor and the active layer to separate the semiconductor structure into a first part and a second part on the first substrate; wherein the second part functions as a low-resistance resistor and loses its make diode behavior, the active layer in the first part is capable of generating light, and the active layer in the second part is incapable of generating light.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation application of a previously filed U.S. patent application Ser. No. 14/204,764 filed on Mar. 11, 2014, entitled as “LIGHT-EMITTING DEVICE AND METHOD FOR MANUFACTURING THE SAME”, which is a continuation-in-part of U.S. patent application Ser. No. 13/517,830, entitled “LIGHT-EMITTING DEVICE AND METHOD FOR MANUFACTURING THE SAME”, filed on Jun. 14, 2012. The disclosures of all references cited herein are incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present application relates to a light-emitting device and the method for manufacturing the same, and more particularly to a light-emitting device comprising a first part and a second part. 
       BACKGROUND 
       [0003]    The light radiation theory of light-emitting device is to generate light from the energy released by the electrons moving between the n-type semiconductor layer and the p-type semiconductor layer. Because the light radiation theory of light-emitting device is different from the incandescent light which heats the filament, the light-emitting device is called a “cold” light source. 
         [0004]    The light-emitting device mentioned above may be mounted with the substrate upside down onto a submount via a solder bump or a glue material to form a light-emitting apparatus. Besides, the submount further comprises one circuit layout electrically connected to the electrode of the light-emitting device via an electrical conductive structure such as a metal wire. 
         [0005]    Moreover, the light-emitting device is more sustainable, long-lived, light and handy, and less power consumption, therefore it is considered as a new light source for the illumination market. The light-emitting device applies to various applications like the traffic signal, backlight module, street light and medical instruments, and is gradually replacing the traditional lighting sources. 
       SUMMARY 
       [0006]    A light-emitting device is provided. The light-emitting device comprises: a semiconductor structure comprising a first type semiconductor layer, a second type semiconductor layer, and an active layer between the first type semiconductor layer and the second type semiconductor layer; and an isolation region through the second type semiconductor and the active layer to separate the semiconductor structure into a first part and a second part on the first substrate; wherein the second part functions as a low-resistance resistor and loses its make diode behavior, the active layer in the first part is capable of generating light, and the active layer in the second part is incapable of generating light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The foregoing aspects and many of the attendant advantages of this application are more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0008]      FIG. 1A  through  FIG. 1G  are schematic diagrams showing the process flow for manufacturing a light-emitting device in accordance with a first embodiment of the present application; 
           [0009]      FIG. 2A  is a schematic diagram showing the current path for testing a light-emitting device in accordance with a first embodiment of the present application; 
           [0010]      FIG. 2B  is a schematic diagram showing the I-V test for a light-emitting device in accordance with a first embodiment of the present application; 
           [0011]      FIG. 3A  through  FIG. 3I  are schematic diagrams showing the process flow for manufacturing a light-emitting device in accordance with a second embodiment of the present application; 
           [0012]      FIG. 4A  through  FIG. 4I  are schematic diagrams showing the process flow for manufacturing a light-emitting device in accordance with a third embodiment of the present application; 
           [0013]      FIG. 5  is a schematic diagram of a backlight module device in accordance with a fourth embodiment of the present application; and 
           [0014]      FIG. 6  is a schematic diagram of an illumination device in accordance with a fifth embodiment of the present application. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    The present application discloses a light-emitting device and a method for manufacturing the same. In order to make the illustration of the present application more explicit, the following description is stated with reference to  FIG. 1  through  FIG. 6 . 
         [0016]      FIG. 1A  through  FIG. 1G  are schematic diagrams showing the process flow for manufacturing a light-emitting device  1  in accordance with a first embodiment of the present application. As  FIG. 1A  shows, a substrate  101  is provided for epitaxial growth, wherein the substrate  101  having a first surface  101   a  and a second surface  101   b.  In the embodiment, the material of the substrate  101  may be GaAs. Next, a semiconductor structure  105  is grown on the first surface  101   a  of the substrate  101  by, for example, metal organic chemical vapor deposition (MOCVD) method, liquid phase deposition (LPD) method, or molecular beam epitaxy (MBE) method. The semiconductor structure  105  comprises a second type semiconductor layer  104 , an active layer  103 , and a first type semiconductor layer  102  stacked on the first surface  101   a  of the substrate  101 , as shown in  FIG. 1B . In the embodiment, the first type semiconductor layer  102  is n-type AlGaInP series material, the active layer  103  is AlGaInP series material, and the second type semiconductor layer  104  is p-type AlGaInP series material. Then, as  FIG. 1C  shows, an isolation region  106   a  penetrating the active layer  103  in the semiconductor structure  105  is formed by an ion implantation. More specifically, the isolation region  106   a  is formed through the first type semiconductor layer  102  and the active layer  103 , and reaches the second type semiconductor layer  104 . Furthermore, the isolation region  106   a  separates the semiconductor structure  105  into a first part  105   b  and the second part  105   a  so the active layer  103  is also separated into a first part  103   b  and a second part  103   a.  In another embodiment, the isolation region comprises a trench  106   b  formed by a wet etching or a dry etching, as shown in  FIG. 1D . Then, a second electrode  108  is formed on the first type semiconductor layer  102   b  of the first part of the semiconductor structure  105   b,  and a first electrode  107  is formed on the first type semiconductor layer  102   a  of the second part of the semiconductor structure  105   a,  so the second electrode  108  and the first electrode  107  are the same conductivity type. The first electrode  107  and the second electrode  108  can be formed simultaneously with the same material. A third electrode  109  is formed on the second surface  101   b  of the substrate  101  as shown in  FIG. 1E (a). The third electrode  109  electrically connects with the second type semiconductor layer  104  so its conductivity type is different from the second electrode  108  and the first electrode  107 . The material of the electrodes  107 ,  108  and  109  comprises metal material such as Cr, Ti, Ni, Pt, Cu, Au, Al, W, Sn, or Ag.  FIG. 1E (b) is an equivalent-circuit diagram of the light-emitting device  1  demonstrating the first part  105   b  and the second part of the semiconductor structure  105   a  are in reverse polarity series connection. Next, an electrical current is injected across the first electrode  107  and the second electrode  108  to cause a reverse-bias to the second part of the semiconductor structure  105   a  and a forward-bias to the first part of the semiconductor structure  105   b  simultaneously. Specifically, a high current density current  110  is injected to the first electrode  107  and goes through the light-emitting device  1 , and the paths of the current  110  are shown in  FIG. 1F (a). The current  110  goes through the second part of the semiconductor structure  105   a  from the first type semiconductor layer  102   a  to the second type semiconductor layer  104   a  to form a path  110   a,  goes through the substrate  101  horizontally to form a path  110   b,  goes through the second type semiconductor layer  104  below the trench  106   b  region horizontally to form a path  110   b ′, and flows to the second electrode  108  through the first part of the semiconductor structure  105   b  from the second type semiconductor layer  104   b  to the first type semiconductor layer  102   b  to form a path  110   c.    FIG. 1F (b) is an equivalent-circuit diagram of the light-emitting device in  FIG. 1F (a). The electrical current  110  from a power supply is applied to the second part  105   a  of the semiconductor structure such that the current density (defined by the current  110  divided by the total surface area of the light-emitting device  1 ) is high enough to cause the second part of the semiconductor structure  105   a  to be reverse-biased and exceed the breakdown voltage V bd  of the second part of the semiconductor structure  105   a,  therefore the diode behavior of the second part  105   a  of the semiconductor structure is permanently destroyed. As a result, the second part of the semiconductor structure  105   a  becomes a resistor having a general low resistance such that the second part of the semiconductor structure  105   a  is capable of allowing a current passing through either in forward direction from the first electrode  107  to the second electrode  108  or in reverse direction from the third electrode  109  to the first electrode  107  as shown in  FIG. 2A  after the diode behavior of the second part  105   a  of the semiconductor structure is permanently broken-down. Namely, when forward-biasing the first part of the semiconductor structure  105   b,  the electrical current  110  is able to flow through the first electrode  107 , the second part of the semiconductor structure  105   a,  the first part of the semiconductor structure  105   b,  and the second electrode  108  to emit light during normal operation after the diode behavior of the second part of the semiconductor structure  105   a  is permanently broken-down. In the embodiment, the current density of the current  110  applied to the second part of the semiconductor structure  105   a  is greater than 80 A/cm 2  or to about 200 A/cm 2  with a duration of 0.1 to 1 second such that the reverse-biasing voltage across the second part of the semiconductor structure  105   a  exceeds the breakdown voltage of the second part of the semiconductor structure  105   a  to cause the diode behavior of the second part of the semiconductor structure  105   a  to be permanently broken-down. In one of the embodiments, the area of the light-emitting device  1  is 12 mils by 12 mils, and a preferable current density applied to the light-emitting device  1  is about 110 A/cm 2  and a preferable duration is about 0.5 second for causing the diode behavior of the second part  105   a  of the semiconductor structure to be permanently destroyed and preventing the second part  105   a  from forming a permanently open circuit. Specifically, to obtain the same result as mentioned above, the current density is inversely proportional to the duration of the current density, for example, when the duration is about 0.1 second, the current density is not more than 200 A/cm 2 . Furthermore, the current is substantially conducted through the semiconductor material of the second part of the semiconductor structure  105   a.  After the diode behavior of the second part of the semiconductor structure  105   a  is permanently broken-down, only the first part of the active layer  103   b  can generate the electromagnetic radiation during operation of the light-emitting device  1  while the second part of the active layer  103   a  can not generate the electromagnetic radiation.  FIG. 1G  is an equivalent-circuit diagram of the light-emitting device  1  after the high current density current  110  is injected to the first electrode  107  and goes through the light-emitting device  1  to cause the diode behavior of the second part of the semiconductor structure  105   a  to be permanently broken-down. The current paths go through the light-emitting device  1  during the I-V test are shown in  FIG. 2A . Injecting a testing current from the third electrode  109  of the light-emitting device  1  through the first part of the semiconductor structure  105   b  from the second type semiconductor layer  104   b  to the first type semiconductor layer  102   b  to form a path A, then obtaining a current vs. voltage curve A as shown in the  FIG. 2B . Injecting a testing current from the first electrode  107  to the second electrode  108  through the second part of the semiconductor structure  105   a  from the first type semiconductor layer  102   a  to the second type semiconductor layer  104   a,  through the substrate  101  horizontally and through the second type semiconductor layer  104  below the trench  106   b  region horizontally respectively, and through the first part of the semiconductor structure  105   b  from the second type semiconductor layer  104   b  to the first type semiconductor layer  102   b  to form a path B, then obtaining a current vs. voltage curve B as shown in the FIG.  2 B. Injecting a testing current from the third electrode  109  to the first electrode  107  through the second part of the semiconductor structure  105   a  from the second type semiconductor layer  104   a  to the first type semiconductor layer  102   a  to form a path C, then obtaining a current vs. voltage curve C as shown in the  FIG. 2B , which indicates that the second part of the semiconductor structure  105   a  forms a resistor with a resistance lower than that of the first part of the semiconductor structure  105   b  (the slope of curve C is steeper than the slope of curve A). The trend of the curve A and the curve B is substantially the same and indicates the electrical property of the path B is the same as the electrical property of the path A in the light-emitting device  1 , which means the first part of the semiconductor structure  105   b  in the light-emitting device  1  can operate normally after the high current density current  110  is injected to the first electrode  107  and flows along the path B. 
         [0017]      FIG. 3A  through  FIG. 31  are schematic diagrams showing the process flow for manufacturing a light-emitting device  2  in accordance with a second embodiment of the present application. As  FIG. 3A  shows, a growth substrate  311  is provided for epitaxial growth, wherein the growth substrate  311  having a first surface  311   a  and a second surface  311   b.  In the embodiment, the material of the growth substrate  311  may be GaAs. A semiconductor structure  305  is grown on the first surface  311   a  of the growth substrate  311  by, for example, metal organic chemical vapor deposition (MOCVD) method, liquid phase deposition (LPD) method, or molecular beam epitaxy (MBE) method. The semiconductor structure  305  comprises a second type semiconductor layer  304 , an active layer  303 , and a first type semiconductor layer  302  stacked on the first surface  311   a  of the growth substrate  311 , as shown in  FIG. 3B . In the embodiment, the first type semiconductor layer  302  is n-type AlGaInP series material, the active layer  303  is AlGaInP series material, and the second type semiconductor layer  304  is p-type AlGaInP series material. As  FIG. 3C  shows, a substrate  301  is provided, a reflecting layer  312  is formed on the substrate  301 , and a bonding layer  313  is formed on the reflecting layer  312 . In  FIG. 3D , the semiconductor structure  305  shown in  FIG. 3B  is connected with the structure shown in  FIG. 3C  by the bonding layer  313 . Then the growth substrate  311  is removed by selectively etching, lapping, polishing, wafer lift-off, or the combination thereof (not shown). 
         [0018]    The substrate  301  is conductive, wherein the material of the substrate  301  comprises metal such as Cu, Al, Mo, metal alloy such as Cu—Sn, Cu—Zn, conductive oxide such as ZnO, SnO, or semiconductor such as Si, AlN, GaAs, SiC, or GaP. The bonding layer  313  is conductive, wherein the material of the bonding layer  313  comprises metal, silver glue, conductive polymer, polymer materials mixed with conductive materials, or anisotropic conductive film. 
         [0019]    As  FIG. 3E  shows, an isolation region  306   a  penetrating the active layer  303  in the semiconductor structure  305  is formed by an ion implantation. More specifically, the isolation region  306   a  is formed through the second type semiconductor layer  304  and the active layer  303 , and reaches the first type semiconductor layer  302  proximal to the substrate  301 . Furthermore, the isolation region  306   a  separates the semiconductor structure  305  into a first part  305   b  and the second part  305   a  so the active layer  303  is also separated into a first part  303   b  and a second part  303   a.  In another embodiment, the isolation region comprises a trench  306   b  formed by a wet etching or a dry etching, as shown in  FIG. 3F . A second electrode  308  is formed on the second type semiconductor layer  304   a  of the second part of the semiconductor structure  305   a,  and a first electrode  307  is formed on the second type semiconductor layer  304   b  of the first part of the semiconductor structure  305   b,  so the second electrode  308  and the first electrode  307  are the same conductivity type. The first electrode  307  and the second electrode  308  can be formed simultaneously with the same material. Then a light-emitting device  2  is formed as shown in  FIG. 3G (a). The material of the electrodes  307  and  308  comprises metal material such as Cr, Ti, Ni, Pt, Cu, Au, Al, W, Sn, or Ag.  FIG. 3G (b) is an equivalent-circuit diagram of the light-emitting device  2  demonstrating the first part  305   b  and the second part of the semiconductor structure  305   a  are in reverse polarity series connection. An electrical current is injected across the first electrode  307  and the second electrode  308  to cause a reverse-bias to the second part of the semiconductor structure  305   a  and a forward-bias to the first part of the semiconductor structure  305   b  simultaneously. Specifically, a high current density current  310  is injected to the first electrode  307  and goes through the light-emitting device  2 , and the paths of the current  310  are shown in  FIG. 3H (a). The current  310  goes through the first part of the semiconductor structure  305   b  from the second type semiconductor layer  304   b  to the first type semiconductor layer  302   b  to form a path  310   a,  goes through the substrate  301  horizontally to form a path  310   b,  goes through the first type semiconductor layer  302  below the trench  306   b  region horizontally to form a path  310   b ′, goes through the bonding layer  313  horizontally to form a path  310   b ″, goes through the reflecting layer  312  horizontally to form a path  310   b ′″ and flows to the second electrode  308  through the second part of the semiconductor structure  305   a  from the first type semiconductor layer  302   a  to the second type semiconductor layer  304   a  to form a path  310   c.  In the embodiment, the current density of the current  310  applied to the second part of the semiconductor structure  305   a  is greater than 80 A/cm 2  or to about 200 A/cm 2  with a duration of 0.1 to 1 second such that the reverse-biasing voltage across the second part of the semiconductor structure  305   a  exceeds the breakdown voltage of the second part of the semiconductor structure  305   a  to cause the diode behavior of the second part of the semiconductor structure  305   a  to be permanently broken-down for forming an electrically conductive path and preventing from forming an open circuit.  FIG. 3H (b) is an equivalent-circuit diagram of the light-emitting device in  FIG. 3H (a). After the diode behavior of the second part of the semiconductor structure  305   a  is permanently broken-down, only the first part of the active layer  303   b  can generate the electromagnetic radiation during operation of the light-emitting device  2  while the second part of the active layer  303   a  can not generate the electromagnetic radiation because a resistor with a low resistance is formed.  FIG. 3I  is an equivalent-circuit diagram of the light-emitting device  2  after the high current density  310  is injected across the first electrode  307  and the second electrode  308  and goes through the light-emitting device  2 . 
         [0020]      FIG. 4A  through  FIG. 41  are schematic diagrams showing the process flow for manufacturing a light-emitting device  3  in accordance with a third embodiment of the present application. As  FIG. 4A  shows, a growth substrate  411  is provided for epitaxial growth, wherein the growth substrate  411  having a first surface  411   a  and a second surface  411   b.  In the embodiment, the material of the growth substrate  411  may be GaAs. A semiconductor structure  405  is grown on the first surface  411   a  of the growth substrate  411  by, for example, metal organic chemical vapor deposition (MOCVD) method, liquid phase deposition (LPD) method, or molecular beam epitaxy (MBE) method. The semiconductor structure  405  comprises a first type semiconductor layer  402 , an active layer  403 , and a second type semiconductor layer  404  stacked on the first surface  411   a  of the growth substrate  411 , as shown in  FIG. 4B . In the embodiment, the first type semiconductor layer  402  is n-type AlGaInP series material, the active layer  403  is AlGaInP series material, and the second type semiconductor layer  404  is p-type AlGaInP series material. As  FIG. 4C  shows, a substrate  401  is provided, and a bonding layer  413  is formed on the substrate  401 . In  FIG. 4D , the semiconductor structure  405  shown in  FIG. 4B  is connected with the structure shown in  FIG. 4C  by the bonding layer  413 . Then the growth substrate  411  is removed by selectively etching, lapping, polishing, wafer lift-off, or the combination thereof (not shown). 
         [0021]    The substrate  401  is non-conductive, wherein the material of the substrate  401  comprises metal oxide such as sapphire, carbon-containing materials such as diamond, dielectric materials, glass, or polymer such as epoxy. The bonding layer  413  is conductive or non-conductive. 
         [0022]    As  FIG. 4E  shows, an isolation region  406   a  penetrating the active layer  403  in the semiconductor structure  405  is formed by an ion implantation. More specifically, the isolation region  406   a  is formed through the first type semiconductor layer  402  and the active layer  403 , and reaches the second type semiconductor layer  404  proximal to the substrate  401 . Furthermore, the isolation region  406   a  separates the semiconductor structure  405  into a first part  405   b  and the second part  405   a  so the active layer  403  is also separated into a first part  403   b  and a second part  403   a.  In another embodiment, the isolation region comprises a trench  406   b  formed by a wet etching or a dry etching to expose the second type semiconductor layer  404 , as shown in  FIG. 4F . A second electrode  408  is formed on the first type semiconductor layer  402   b  of the first part of the semiconductor structure  405   b,  and a first electrode  407  is formed on the first type semiconductor layer  402   a  of the second part of the semiconductor structure  405   a,  so the second electrode  408  and the first electrode  407  are the same conductivity type. The first electrode  407  and the second electrode  408  can be formed simultaneously with the same material. Then a light-emitting device  3  is formed as shown in  FIG. 4G (a). The material of the electrodes  407  and  408  comprises metal material such as Cr, Ti, Ni, Pt, Cu, Au, Al, W, Sn, or Ag.  FIG. 4G (b) is an equivalent-circuit diagram of the light-emitting device  3  demonstrating the first part  405   b  and the second part of the semiconductor structure  405   a  are in reverse polarity series connection. Next, an electrical current is injected across the first electrode  407  and the second electrode  408  to cause a reverse-bias to the second part of the semiconductor structure  405   a  and a forward-bias to the first part of the semiconductor structure  405   b  simultaneously. Specifically, a high current density current  410  is injected to the first electrode  407  and goes through the light-emitting device  3 , and the paths of the current  410  are shown in  FIG. 4H (a). The current  410  goes through the second part of the semiconductor structure  405   a  from the first type semiconductor layer  402   a  to the second type semiconductor layer  404   a  to form a path  410   a,  goes through the second type semiconductor layer  404  below the trench  406   b  region horizontally to form a path  410   b , goes through the bonding layer  413  (formed of conductive material) horizontally to form a path  410   b ′ and flows to the second electrode  408  through the first part of the semiconductor structure  405   b  from the second type semiconductor layer  404   b  to the first type semiconductor layer  402   b  to form a path  410   c.  In the embodiment, the current density of the current  410  is greater than 80 A/cm 2  or to about 200 A/cm 2  with a duration of 0.1 to 1 second such that the reverse-biasing voltage across the second part of the semiconductor structure  405   a  exceeds the breakdown voltage of the second part of the semiconductor structure  405   a  to cause the diode behavior of the second part of the semiconductor structure  405   a  to be permanently broken-down for forming an electrically conductive path and preventing from forming an open circuit.  FIG. 4H (b) is an equivalent-circuit diagram of the light-emitting device in  FIG. 4H (a). After the diode behavior of the second part of the semiconductor structure  405   a  is permanently broken-down, only the first part of the active layer  403   b  can generate the electromagnetic radiation during operation of the light-emitting device  3  while the second part of the active layer  403   a  can not generate the electromagnetic radiation because a resistor with a low resistance is formed.  FIG. 41  is an equivalent-circuit diagram of the light-emitting device  3  after the high current density current  410  is injected across the first electrode  307  and the second electrode  308  and goes through the light-emitting device  3 . 
         [0023]      FIG. 5  shows a schematic diagram of a backlight module device  500  in accordance with a fourth embodiment of the present application. The backlight module device  500  comprises a light source device  510  having the light-emitting device  1 ,  2 , or  3  in one of the above mentioned embodiments, an optics device  520  deposited on the light extraction pathway of the light source device  510 , and a power supplement  530  which provides a predetermined power to the light source device  510 . In  FIG. 5  shows only the light-emitting device  1 , but the light-emitting device includes but is not limited to light-emitting device  1 ,  2 ,  3  or the combination thereof. 
         [0024]      FIG. 6  shows a schematic diagram of an illumination device  600  in accordance with a fifth embodiment of the present application. The illumination device  600  can be automobile lamps, street lights, flashlights, indicator lights and so forth. The illumination device  600  comprises a light source device  610  having the light-emitting device  1 ,  2 , or  3  in one of the above mentioned embodiments, a power supplement  620  which provides a predetermined power to the light source device  610 , and a control element  630  which controls the current driven into the light source device  610 . In  FIG. 6  shows only the light-emitting device  1 , but the light-emitting device includes but is not limited to light-emitting device  1 ,  2 ,  3  or the combination thereof. 
         [0025]    In accordance with the embodiments in the application, the first type semiconductor layer  102 ,  302 , or  402  and the second type semiconductor layer of the semiconductor structure  104 ,  304 , or  404  are two single-layer structures or two multiple layers structure (“multiple layers” means two or more than two layers) having different electrical properties, polarities, dopants for providing electrons or holes respectively. If the first type semiconductor layer and the second type semiconductor layer are composed of the semiconductor materials, the conductivity type can be any two of p-type, n-type, and i-type. The active layer  103 ,  303 , or  403  disposed between the first type semiconductor layer  102 ,  302 , or  402  and the second type semiconductor layer  104 ,  304 , or  404  is a region where the light energy and the electrical energy could transfer or could be induced to transfer. 
         [0026]    In another embodiment of this application, the light emission spectrum of the semiconductor structure  105 ,  305 , or  405  after transferring can be adjusted by changing the physical or chemical arrangement of one layer or more layers in the active layer. The material of the active layer can be AlGaInP series material or AlGaInN series material. The structure of the active layer can be a single heterostructure (SH), a double heterostructure (DH), a double-side double heterostructure (DDH), or a multi-quantum well (MQW) structure. Besides, the wavelength of the emitted light could also be adjusted by changing the number of the pairs of the quantum well in a MQW structure. 
         [0027]    In one embodiment of this application, a buffer layer (not shown) could be optionally formed between the substrate and the semiconductor structure. The buffer layer between two material systems can be used as a buffer system. For the structure of the light-emitting device, the buffer layer is used to reduce the lattice mismatch between two material systems. On the other hand, the buffer layer could also be a single layer, multiple layers, or a structure to combine two materials or two separated structures where the material of the buffer layer can be organic, inorganic, metal, semiconductor, and so on, and the function of the buffer layer can be as a reflection layer, a heat conduction layer, an electrical conduction layer, an ohmic contact layer, an anti-deformation layer, a stress release layer, a stress adjustment layer, a bonding layer, a wavelength converting layer, a mechanical fixing structure, and so on. The material of the buffer layer can be AlN, GaN, InP, GaP or other suitable materials. The fabricating method of the buffer layer can be sputter or atomic layer deposition (ALD). 
         [0028]    A contact layer (not shown) can also be optionally formed on the semiconductor structure. The contact layer is disposed on the second type semiconductor layer opposite to the active layer. Specifically speaking, the contact layer could be an optical layer, an electrical layer, or the combination of the two. An optical layer can change the electromagnetic radiation or the light from or entering the active layer. The term “change” here means to change at least one optical property of the electromagnetic radiation or the light. The above mentioned property includes but is not limited to frequency, wavelength, intensity, flux, efficiency, color temperature, rendering index, light field, and angle of view. An electrical layer can change or be induced to change the value, density, or distribution of at least one of the voltage, resistance, current, or capacitance between any pair of the opposite sides of the contact layer. The composition material of the contact layer includes at least one of oxide, conductive oxide, transparent oxide, oxide with 50% or higher transmittance, metal, relatively transparent metal, metal with 50% or higher transmittance, organic material, inorganic material, fluorescent material, phosphorescent material, ceramic, semiconductor, doped semiconductor, and undoped semiconductor. In certain applications, the material of the contact layer is at least one of indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide, indium zinc oxide, zinc aluminum oxide, and zinc tin oxide. If the material is relatively transparent metal, the thickness is about 0.005 μm-0.6 μm. 
         [0029]    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 application without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present application covers modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents. 
         [0030]    Although the drawings and the illustrations above are corresponding to the specific embodiments individually, the element, the practicing method, the designing principle, and the technical theory can be referred, exchanged, incorporated, collocated, coordinated except they are conflicted, incompatible, or hard to be put into practice together. 
         [0031]    Although the present application has been explained above, it is not the limitation of the range, the sequence in practice, the material in practice, or the method in practice. Any modification or decoration for present application is not detached from the spirit and the range of such.