Patent Publication Number: US-9847459-B2

Title: Light emitting device and lighting system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of copending application Ser. No. 14/930,164, filed on Nov. 2, 2015, which claims priority under 35 U.S.C. 119(a) to Korean Patent Application No. 10-2014-0151308 filed on Nov. 3, 2014, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The embodiment relates to a light emitting device, a method of manufacturing a light emitting device, a light emitting device package and a lighting system. 
     A light emitting device (LED) includes a p-n junction diode having a characteristic of converting electric energy into light energy. The p-n junction diode may be formed by combining group III-V elements of the periodic table. The LED may represent various colors by adjusting the compositional ratio of compound semiconductors. 
     When a forward voltage is applied to an LED, electrons of an n layer are combined with holes of a player, so that energy corresponding to an energy gap between a conduction band and a valance band may be released. The LED emits the energy as the light. 
     For instance, a nitride semiconductor represents superior thermal stability and wide band gap energy, so that the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and UV light emitting devices employing the nitride semiconductor have already been commercialized and extensively used. 
     A light emitting device may be classified into a lateral type and a vertical type according to the positions of an electrode. 
     The lateral-type light emitting device among light emitting devices according to the related art is formed in a structure in which a nitride semiconductor layer is formed on a substrate, and two electrode layers are disposed on the nitride semiconductor layer. 
     Meanwhile, the lateral-type light emitting device according to the related art has a great loss caused at the active layer able to emit light since mesa etching is performed over a large area. In order to compensate for the loss, various attempts are performed to ensure a wider active layer. 
     For example, according to the related art, there has been an attempt to secure a relatively larger area of an active layer by forming an electrode making contact with a nitride semiconductor layer in a through-electrode type to allow the electrode to be partially and electrically connected to the nitride semiconductor layer so that a removed area of the active area is reduced. However, the related art has a problem in reliability since an operating voltage VF is increased, and thus, the improvement is required. 
     In addition, according to the related art, the light extraction efficiency may be degraded due to the light absorption of the electrode layer. 
     SUMMARY 
     The embodiment is to provide a light emitting device having superior light efficiency and reliability, a method of manufacturing a light emitting device, and a light emitting device package and a lighting system. 
     In addition, the embodiment is to provide a light emitting device having superior light efficiency and reliability, a method of manufacturing a light emitting device, and a light emitting device package and a lighting system. 
     To achieve the object, according to the embodiment, there is provided a light emitting device which includes: a substrate  105 ; a first conductive semiconductor layer  112  on the substrate  105 ; an active layer  114  on the first conductive semiconductor layer  112 ; a second conductive semiconductor layer  116  on the active layer  114 ; an contact layer  120  on the second conductive semiconductor layer  116 ; an insulating layer  130  on the contact layer  120 ; a first branch electrode  146  electrically connected to the first conductive semiconductor layer  112 ; a plurality of first via electrodes  145  connected to the first branch electrode  146  and electrically connected to the first conductive semiconductor layer  112  by passing through the insulating layer  130 ; a first pad electrode  142  electrically connected to the first branch electrode  146 ; a second pad electrode  152  contacts the contact layer  120  by passing through the insulating layer  130 ; a second branch electrode  156  connected to the second pad electrode  152  and disposed on the insulating layer  130 ; and a plurality of second via electrodes  155  provided through the insulating layer  130  to electrically connect the second branch electrode  156  to the contact layer  120 . 
     In addition, a light emitting device according to the embodiment includes a light emitting structure  110  including a first conductive semiconductor layer  112 , an active layer  114  and a second conductive semiconductor layer  116 ; a first branch electrode  146  electrically connected to the first conductive semiconductor layer  112 ; a plurality of third via electrodes  149  connected to the first branch electrode  146  and electrically connected to the first conductive semiconductor layer  112  by passing through a predetermined insulating layer  130 ; a second branch electrode  156  electrically connected to the second conductive semiconductor layer  116  while interposing an contact layer  120  between the second branch electrode  156  and the second conductive semiconductor layer  116 ; and a plurality of second via electrodes  155  disposed between the second branch electrode  156  and the contact layer  120  while passing through the insulating layer  130 . 
     One of the third via electrodes  149  electrically connected to the first conductive semiconductor layer  112  has a third horizontal width W 3  wider than a second horizontal width W of the second via electrode  155  disposed on the contact layer  130 . 
     A light system may include a light emitting unit having a light emitting device. 
     According to the embodiment, the embodiment can provide a light emitting device having superior light efficiency and reliability, a method of manufacturing a light emitting device, and a light emitting device package and a lighting system. 
     In addition, according to the embodiment, the embodiment can provide a light emitting device having superior light extraction efficiency and reliability, a method of manufacturing a light emitting device, and a light emitting device package and a lighting system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing a light emitting device according to a first embodiment. 
         FIG. 2  is a first sectional view taken along line I-I′ of  FIG. 1 . 
         FIG. 3  is an enlarged view of part A of  FIG. 1 . 
         FIG. 4  is a second sectional view taken along line II-II′ of  FIG. 1 . 
         FIG. 5  is a photograph of a part of a light emitting device according to the related art. 
         FIG. 6  is a third sectional view taken along line I-I of  FIG. 1  according to a second embodiment. 
         FIG. 7  is a fourth sectional view taken along line II-II′ of  FIG. 1  according to the second embodiment. 
         FIG. 8  is a fifth sectional view taken along line II-II′ of  FIG. 1  according to a third embodiment. 
         FIG. 9  is a plan view showing a light emitting device according to a fourth embodiment. 
         FIG. 10  is a sixth sectional view taken along line III-III′ of  FIG. 9 . 
         FIG. 11  is a seventh sectional view taken along line IV-IV′ of  FIG. 9 . 
         FIG. 12  is an eighth sectional view taken along line III-III′ of  FIG. 9 . 
         FIG. 13  is a sectional view showing a light emitting device package according to an embodiment. 
         FIG. 14  is a perspective views showing a lighting apparatus according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the description of the embodiments, it will be understood that, when a layer (or film), an area, a pattern, or a structure is referred to as being “on” or “under” another substrate, another layer (or film), another area, another pad, or another pattern, it can be “directly” or “indirectly” over the other substrate, layer (or film), area, pad, or pattern, or one or more intervening layers may also be present. Such a position of the layer has been described with reference to the drawings. 
     Embodiment 
       FIG. 1  is a plan view showing a light emitting device  100  according to a first embodiment.  FIG. 2  is a first sectional view taken along line I-I′ of  FIG. 1 .  FIG. 4  is a second sectional view taken along line II-II′ of  FIG. 1 . 
     As shown in  FIG. 2 , a light emitting device  100  according to the first embodiment may include a substrate  105 , a first conductive semiconductor layer  112  formed on the substrate  105 , an active layer  114  formed on the first conductive semiconductor layer  112 , and a second conductive semiconductor layer  116  formed on the active layer  114 . The first and second conductive semiconductor layers  112  and  116  and the active layer  114  may constitute a light emitting structure  110 . 
     In addition, as shown in  FIG. 2 , the light emitting device  100  according to the first embodiment may include an contact layer  120  formed on the second conductive semiconductor layer  116 , an insulating layer  130  formed on the contact layer  120 , a first branch electrode  146  electrically connected to the first conductive semiconductor layer  112 , and a first pad electrode  142  connected to the first branch electrode  146  so that the first pad electrode  142  is electrically connected to the first conductive semiconductor layer  112 . 
     In addition, the light emitting device  100  according to the first embodiment may include a plurality of first via electrodes  145  which are connected to the first branch electrode  146  and pass through the insulating layer  130  such that the first via electrodes  145  are electrically connected to the first conductive semiconductor layer  112 . 
     A first electrode  140  may include the first pad electrode  142 , the first branch electrode  146  and the first via electrodes  145 . 
     As shown in  FIG. 4 , the light emitting device  100  according to the first embodiment may include a second pad electrode  152  passing through the insulating layer  130  to make contact with an contact layer  120 , a second branch electrode  156  disposed on the insulating layer  130  while being connected to the second pad electrode  152 , and a second via electrode  155  interposed between the second branch electrode  156  and the contact layer  120  while passing through the insulating layer  130 . 
     A second electrode  150  may include the second pad electrode  152 , the second branch electrode  156  and the second via electrode  155 . 
     Hereinafter, the characteristics of the light emitting device  100  according to an embodiment will be described with reference to  FIGS. 2 a    and  3 . Although the lateral-type light emitting device according to the first embodiment is shown in  FIGS. 1, 2   a  and  3 , the embodiment is not limited thereto. 
     According to the first embodiment, the substrate  105  may include an insulating substrate or a conductive substrate. For example, the substrate  105  may include at least one of sapphire (Al 2 O 3 ), SiC, Si, GaAs, GaN, ZnO, GaP, InP, Ge, and Ga 2 O 3 , or the combination thereof, but the embodiment is not limited thereto. A predetermined concave-convex structure (not shown) may be formed on the substrate  105  to improve light extraction efficiency, but the embodiment is not limited thereto. 
     According to the first embodiment, a predetermined buffer layer (not shown) is formed on the substrate  105  to reduce lattice mismatch between the light emitting structure  110  and the substrate  105 . The buffer layer may include at least one of GaN, InN, AlN, InGaN, AlGaN, InAlGaN, and AlInN, but the embodiment is not limited thereto. 
     According to the first embodiment, the light emitting device  100  may include the light emitting structure  110  formed on the substrate  105  or the buffer layer. The light emitting structure  110  may include the first conductive semiconductor layer  112  on the substrate  105 , the active layer  114  on the first conductive semiconductor layer  112 , and the second conductive semiconductor layer  116  on the active layer  114 . 
     The first conductive semiconductor layer  112  may be realized using a group III-V compound semiconductor doped with first conductive dopants. For example, when the first conductive semiconductor layer  112  is an N type semiconductor layer, the first conductive dopants may include Si, Ge, Sn, Se, and Te serving as N type dopants, but the embodiment is not limited thereto. 
     The first conductive semiconductor  112  may include a semiconductor material having a composition formula of In x Al y Ga 1-x-y N (0≦x≦1, 0≦y≦1, 0≦x+y≦1). For example, the first conductive semiconductor layer  112  may include at least one of GaN, InN, AlN, InGaN, AlGaN, InAlGaN, AlInN, AlGaAs, InGaAs, AlInGaAs, GaP, AlGaP, InGaP, AlInGaP, and InP. 
     In the active layer  114 , electrons injected through the first conductive semiconductor layer  112  and holes injected through the second conductive semiconductor layer  116  thereafter meet each other, so that light having energy determined by the inherent energy band of a material constituting the active layer (light emission layer) is emitted. 
     The active layer  114  may include at least one of a single quantum well, a multi-quantum well (MQW), a quantum-wire structure, and a quantum dot structure. 
     The active layer  114  may have a well layer/barrier layer. For example, the active layer  114  may be formed in a pair structure having at least one of InGaN/GaN, InGaN/InGaN, GaN/AlGaN, InAlGaN/GaN, GaAs/AlGaAs, GaP/AlGaP, InGaAs/AlGaAs and InGaP/AlGaP, but the embodiment is not limited thereto. The well layer may include a material having a bandgap lower than that of the barrier layer. 
     According to the first embodiment, an electron blocking layer (not shown) may be formed on the active layer  114 . For example, the electron blocking layer may include a semiconductor based on Al x In y Ga (1-x-y) N (0≦x1, 0≦y≦1), and may have the energy bandgap higher than that of the active layer  114 . The electron blocking layer  160  is implanted with P type ions to effectively block overflowed electrons, so that hole injection efficiency may be increased. 
     According to the embodiment, the second conductive semiconductor layer  116  may include a group III-V compound semiconductor layer doped with second conductive dopants. For example, the second conductive semiconductor layer  116  may include a semiconductor material having a composition formula of In x Al y Ga 1-x-y N (0≦x≦1, 0≦y≦1, 0≦x+y≦1). When the second conductive semiconductor layer  116  includes a P type semiconductor layer, the second conductive dopant may include Mg, Zn, Ca, Sr, or Ba serving as the second conductive dopant. 
     As shown in  FIG. 2 a   , according to the first embodiment, the light emitting device  100  may include the contact layer  120  on the second conductive semiconductor layer  116 , the insulating layer  130  on the contact layer  120 , the first branch electrode  146  electrically connected with the first conductive semiconductor layer  112 , the first via electrodes  145  connected with the first branch electrode  146  and passing through the insulating layer  130  to be electrically connected to the first conductive semiconductor layer  112 , and the first pad electrode  142  connected with the first branch electrode  140  so that the first pad electrode  142  is electrically connected to the first conductive semiconductor layer  112 . 
     The contact layer  120  may be formed by multi-layering single metal, a metal alloy, and a metallic oxide so that carriers may be efficiently implanted. The contact layer  120  includes a transmissive electrode to improve the light extraction efficiency and to lower the operating voltage, so that the reliability may be improved. 
     For example, the contact layer  120  may include at least one of ITO (indium tin oxide), IZO (indium zinc oxide), IZTO (indium zinc tin oxide), IAZO (indium aluminum zinc oxide), IGZO (indium gallium zinc oxide), IGTO (indium gallium tin oxide), AZO (aluminum zinc oxide), ATO (antimony tin oxide), GZO (gallium zinc oxide), IZON (IZO Nitride), AGZO (Al—Ga ZnO), IGZO (In—Ga ZnO), ZnO, IrOx, RuOx, NiO, RuOx/ITO, Ni/IrOx/Au, Ni/IrOx/Au/ITO, Ag, Ni, Cr, Ti, Al, Rh, Pd, Ir, Ru, Mg, Zn, Pt, Au, and Hf, or the combination thereof, but the embodiment is not limited thereto. 
     The insulating layer  130  may include an electrical insulator including an oxide or a nitride, but the embodiment is not limited thereto. The insulating layer  130  may perform a short protection function. For example, the insulating layer  130  may be interposed between the first via electrode  145 , the contact layer  120 , the second conductive semiconductor layer  116  and the active layer  114 , so that the first via electrode  145 , the contact layer  120 , the second conductive semiconductor layer  116  and the active layer  114  are prevented from being short circuited with each other. 
     The insulating layer  130  is formed of a transmissive insulating material so that the light extraction efficiency may be improved. 
     As shown in  FIG. 2 , according to the first embodiment, the active layer  114  is not mesa-etched at the position in which the first pad electrode  142  is formed, thereby securing an active layer region to improve internal light emission efficiency, and to improve light efficiency due to current spreading. 
     Thus, according to the first embodiment, the first pad electrode  142  is disposed on the insulating layer  130 , so that the first pad electrode  142  may be connected to the first branch electrode  146 . The first pad electrode  142  may vertically overlap the insulating layer  130  and the contact layer  120 . The contact layer  120  is provided under the first pad electrode  142  while interposing the insulating layer  130  between the contact layer  120  and the first pad electrode  142 , thereby widening a light emission area to improve carrier injection efficiency, so that light efficiency may be improved. 
     According to the first embodiment, as shown in  FIG. 2 , the contact layer  120 , the second conductive semiconductor layer  116  and the active layer  114  are partially removed through the mesa-etching process, so that the first conductive semiconductor layer  112  may be partially exposed. 
     The first branch electrode  146  may be electrically connected to the exposed first conductive semiconductor layer  112 . 
     According to the first embodiment, an N type branch electrode structure sufficiently secures a contact area with an N type semiconductor layer to prevent the operating voltage from being increased so that the reliability of the device may be improved. The P type branch electrode employs a point contact structure to contribute to current spreading. The second conductive semiconductor layer  116  makes contact with the contact layer  120  to prevent the operating voltage from being increased, so that the reliability and the light emission efficiency of the device may be maximized. 
     To this end, according to the first embodiment, as shown in  FIGS. 1 and 2   a , the first horizontal width W 1  of one of the first via electrodes  145  electrically connected to the first conductive semiconductor layer  112  is longer than the first distance D 1  between the first via electrodes  145 , so that the area, in which the first via electrode  145  is electrically connected to the first conductive semiconductor layer  112 , may be sufficiently secured, thereby preventing the operating voltage from being increased to improve the reliability of the light emitting device. 
     In addition, according to the second embodiment, as shown in  FIG. 4 , the second horizontal width W 2  of one of the second via electrodes  155  electrically connected to the contact layer  120  is longer than the second distance D 2  between the second via electrodes  155 , so that the area, in which the second via electrode  155  is electrically connected to the contact layer  120 , may be sufficiently secured, thereby preventing the operating voltage from being increased to improve the reliability of the light emitting device. 
     Table 1 shows the electrical characteristics of an embodiment example and a comparative example for comparison. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Po (mW) 
                 Vf (V) 
                 Current (mA) 
                 WPE (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Embodiment 
                 107.0 
                 2.847 
                 65 
                 57.82 
               
               
                 example 
               
               
                 Comparative 
                 102.84 
                 2.864 
                 65 
                 55.24 
               
               
                 example 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, according to the first embodiment, a first horizontal width W 1  of one of the first via electrodes  145  electrically connected to the first conductive semiconductor layer  112  is set to be longer than a first distance D 1  between the first via electrodes  145 , and a second horizontal width W 2  of one of the second via electrodes  155  electrically connected to the contact layer  120  is set to be longer than a first distance D 2  between the second via electrodes  155 . According to the comparative example, the horizontal width of a via electrode of a light emitting device to which a point contact is applied is substantially equal to a distance between the via electrodes. —   
     As described above, according to the related art, an attempt to secure a wider active layer is performed based on the electrical connection with the nitride semiconductor layer through a via electrode. However, the related art has a problem in reliability since the operating voltage VF is increased. 
     As shown in Table 1, when the first embodiment is applied, as compared with the related art, the operating voltage VF is reduced, so that the reliability is improved. In addition, the intensity of light (Po) is increased from 102.84 mW to 107 mW, so that the wall-plug efficiency (WPE) is increased by about 2.5% from 55.24% to 57.82%. —   
     Meanwhile, in case of a point contact structure according to the related art, an issue of increasing the operating voltage by varying a metal layer according to a partial contact has been raised. 
     For example,  FIG. 5  is a photo of a light emitting device according to the related art, where a light emitting structure  10  according to the related art includes a GaN layer, and an electrode layer  20  includes a Cr layer  21 , an Al layer  22  and a Ni layer  23 . 
     According to the related art, when the electrode layer  20  is formed on the light emitting structure  10 , as temperature is increased, inter metallic compounds I are generated, so that the electrode layer  20  is brittle and the operating voltage is increased, thereby raising an issue in electrical reliability. 
     According to the first embodiment, the first horizontal width W 1  of one of the first via electrodes  145  electrically connected to the first conductive semiconductor layer  112  is controlled to be longer than the first distance D 1  between the first via electrodes  145 , so that the electrical contact area with the first conductive semiconductor layer  112  may be sufficiently secured. Thus, the center current crowding of the light emitting device may be minimized so that the light efficiency is improved. In addition, the electrical reliability may be improved so that the light efficiency is improved. 
     According to the first embodiment, the first horizontal width W 1  of the first via electrode  145  electrically connected to the first conductive semiconductor layer  112  may be 2.5 times or more of the first distance D 1  between the first via electrodes  145 . 
     For example, according to the first embodiment, the first horizontal width W 1  of one of the first via electrodes  145  may be equal to or more than about 50 μm and the first distance D 1  between the first via electrodes  145  may be about 20 μm, but the embodiment is not limited thereto. When the first horizontal width W 1  of one of the first via electrodes  145  is less than about 50 μm, due to current crowding, the operating voltage Vf may be increased to exert an influence on the reliability. 
     For example, the first embodiment, the first horizontal width W 1  of one of the first via electrodes  145  may be in the range of about 50 μm to about 70 μm and the first distance D 1  between the first via electrodes  145  may be in the range of about 15 μm to 25 μm, but the embodiment is not limited thereto. 
     Although the horizontal width of the via electrode of the comparative example shown in Table 1 is about 20 μm, the first horizontal width W 1  of the first via electrode  145  according to the first embodiment is controlled to be in the range of about 50 μm to about 70 μm, preferably, about 54 μm to about 66 μm, so that the electrical contact area with the first conductive semiconductor layer  112  may be sufficiently secured to minimize the center current crowding of the light emitting device chip, thereby improving the electrical reliability as well as the light efficiency. 
     As the comparative example, when the horizontal width of the via electrode is approximate to the distance between the via electrodes, the contact area between the first conductive semiconductor layer and the via electrode is insufficient to secure significant light intensity and electrical reliability. 
       FIG. 3  is an enlarged view of part A of  FIG. 1 . 
     Referring to  FIGS. 1 to 3 , according to the embodiment, when viewed from the top, a second thickness T 2  of one of the second via electrodes  155  making contact with the contact layer  120  is thicker than a first thickness T 1  of the second branch electrode  156 , so that the area substantially making contact with the contact layer  120  is widely secured and the remaining areas are set to be narrow. Thus, the electrical reliability may be improved and. degradation of the light extraction efficiency, which may be caused as the emitted light is reflected or blocked by the branch electrode, can be prevented. 
     For example, when a high current is applied and the second thickness T 2  of one of the second via electrode  155  is relatively enlarged when viewed from the top, the electrical reliability may be improved. 
     Although not shown in any drawings, the first electrode  140  may employ technical properties of the second electrode  150  including the second branch electrode  156  having the first thickness T 1  and the second via electrode  155  having the second thickness T 2 . 
       FIG. 6  is a third sectional view of a light emitting device  102  taken along line I-I′ of  FIG. 1  according to a second embodiment.  FIG. 7  is a fourth sectional view of a light emitting device taken along line II-II′ of  FIG. 1  according to the second embodiment. 
     As shown in  FIG. 6 , according to the second embodiment, the first electrode  140  may include a first contact branch electrode  144  making contact with the first conductive semiconductor layer  112  and a first reflective branch electrode  147  disposed on the first via electrode  145 . 
     According to the second embodiment, by employing the first contact branch electrode  144  making contact with the first conductive semiconductor layer  112 , the contact property between the first via electrode  145  and the first conductive semiconductor layer  112  may be secured at the maximum, so that the operating voltage is reduced to improve the electrical reliability. 
     For example, the first contact branch electrode  144  may include at least one of Cr, Ni, Ti, Rh, Pd, Ir, Ru, Pt, Au and Hf, or the combination thereof, but the embodiment is not limited thereto. 
     In addition, according to the embodiment, the first reflective branch electrode  147  is provided at a lower portion of the first branch electrode  146 , so that the light absorption by the first branch electrode  146  may be minimized, thereby improving the external light extraction efficiency. 
     The first reflective branch electrode  147  may include at least one of Ag, Al, Ni, Ti, Rh, Pd, Ir, Ru, Mg, Zn, Pt, Au, and Hf, or the combination thereof, but the embodiment is not limited thereto. 
     The first reflective branch electrode  147  may be formed in a multi-layered structure, but the embodiment is not limited thereto. For example, if the first reflective branch electrode  147  is formed to have two layers, the first reflective branch electrode  147  may include Al/Ni or Ag/Ni. If the first reflective branch electrode  147  is formed to have a single layer, the first reflective branch electrode  147  may include a distributed bragg reflector (DBR), but the embodiment is not limited thereto. 
     In addition, as shown in  FIG. 7 , the second electrode  150  according to the second embodiment may include the second reflective branch electrode  157  which is provided at an lower portion of the second branch electrode  156 , so that the light absorption by the second branch electrode  156  may be minimized, thereby improving the external light extraction efficiency. 
     The second reflective branch electrode  157  may include at least one of Ag, Al, Ni, Ti, Rh, Pd, Ir, Ru, Mg, Zn, Pt, Au, and Hf, or the combination thereof, but the embodiment is not limited thereto. The second reflective branch electrode  157  may be formed in a multi-layered structure, but the embodiment is not limited thereto. 
       FIG. 8  is a fifth sectional view taken along line II-II′ of  FIG. 1  according to a third embodiment. 
     According to the third embodiment, the second electrode  150  may include a second reflective via electrode  154  at an outside of the second via electrode  155 . 
     The second reflective via electrode  154  may be interposed between the contact layer  120  and the second via electrode  155 . The second reflective via electrode  154  may surround the side surface of the second via electrode  155 , but the embodiment is not limited thereto. 
     According to the third embodiment, since the second reflective via electrode  154  is provided to the outside of the second via electrode  155 , the light absorption by the second via electrode  155  may be minimized. 
       FIG. 9  is a plan view showing a light emitting device according to a fourth embodiment.  FIG. 10  is a sixth sectional view taken along line III-III′ of  FIG. 9 .  FIG. 11  is a seventh sectional view taken along line IV-IV′ of  FIG. 9 . 
     The light emitting device  104  according to the fourth embodiment may include a light emitting structure  110  including a first conductive semiconductor layer  112 , an active layer  114  and a second conductive semiconductor layer  116 , a first branch electrode  146  electrically connected to the first conductive semiconductor layer  112 , a plurality of third via electrodes  149  connected to the first branch electrode  146  and electrically connected to the first conductive semiconductor layer  112  by passing through a predetermined insulating layer  130 , a second branch electrode  156  electrically connected to the second conductive semiconductor layer  116  while interposing an contact layer  120  therebetween, and a plurality of second via electrodes  155  disposed between the second electrode  156  and the contact layer  120  while passing through the insulating layer  130 . 
     The fourth embodiment may employ technical properties of the first to third embodiments. 
     As shown in  FIG. 9 , according to the fourth embodiment, the third horizontal width W 3  of one of the third via electrodes  149  electrically connected to the first conductive semiconductor layer  112  may be greater than the second horizontal width W 2  of the second via electrode disposed on the contact layer  130 . 
     According to the fourth embodiment, the third horizontal width W 3  of the third via electrode  149  electrically connected to the first conductive semiconductor layer  112  is controlled to be greater than the second horizontal width W 2  of the second via electrode  155  electrically connected to the contact layer  120 , so that the area of the third via electrode  149  making electrical contact with the first conductive semiconductor layer  112  may be sufficiently secured on the central portion of a chip of which the current crowding is greatly issued. Thus, the center current crowding of the central portion may be minimized so that the light efficiency is improved. In addition, the electrical reliability may be improved so that the light efficiency is improved. 
     In addition, as shown in  FIG. 9 , according to the fourth embodiment, the third horizontal width W 3  of the third via electrode  149  connected to the first branch electrode  146  may be about three times or more of a third distance D 3  between the third via electrodes  149 . Thus, the third via electrodes  149  may be disposed to the first branch electrodes  146  by assigning two third via electrodes  149  to one first branch electrode  146 . 
     According to the fourth embodiment, the third distance D 3  between the third via electrodes  149  may be longer than the second distance D 2  between the second via electrodes  155  for the purpose of current spreading. For example, the third distance D 3  between the third via electrodes  149  may be secured to be about 100 μm or more for the purpose of current spreading so that current crowding may be prevented and the electrical reliability may be ensured due to current spreading. 
     According to the fourth embodiment, the area of the third via electrode  149  making electrical contact with the first conductive semiconductor layer  112  may be sufficiently secured to prevent the operating voltage from being increased, so that the reliability of a light emitting device may be more improved. 
       FIG. 12  is an eighth sectional view taken along line III-III′ of  FIG. 9 . 
     As shown in  FIG. 12 , the first electrode  140  of the light emitting device according to the fourth embodiment may include the third reflective branch electrode  147  which is provided at an lower portion of the first branch electrode  146 , so that the light absorption by the first branch electrode  146  may be minimized, thereby improving the external light extraction efficiency. 
     The third reflective branch electrode  147  may include at least one of Ag, Al, Ni, Ti, Rh, Pd, Ir, Ru, Mg, Zn, Pt, Au, and Hf, or the combination thereof, but the embodiment is not limited thereto. The third reflective branch electrode  147  may be formed in a multi-layered structure, but the embodiment is not limited thereto. 
     According to the embodiment, the embodiment can provide a light emitting device having superior light efficiency and reliability, a method of manufacturing a light emitting device, and a light emitting device package and a lighting system. 
     In addition, according to the embodiment, the embodiment can provide a light emitting device having superior light extraction efficiency and reliability, a method of manufacturing a light emitting device, and a light emitting device package and a lighting system. 
       FIG. 13  is a sectional view showing a light emitting device package in which the light emitting device according to an embodiment is mounted. 
     The light emitting device package according to an embodiment may include a package body part  205 , third and fourth electrode layers  213  and  214  mounted on the package body part  205 , a light emitting device  100  mounted on the package body part  205  and electrically connected with the third and fourth electrode layers  213  and  214 , and a molding member  230  having phosphor  232  and surrounding the light emitting device  100 . 
     The third and fourth electrode layers  213  and  214  are electrically isolated from each other to supply power to the light emitting device  100 . In addition, the third and fourth electrode layers  213  and  214  reflect light emitted from the light emitting device  100  to improve light efficiency, and emitting heat generated from the light emitting device  100  to an outside. 
     The light emitting device  100  may be electrically connected with the third electrode layer  213  and/or the fourth electrode layer  214  through one of a wire scheme, a flip-chip scheme and a die-bonding scheme. 
       FIG. 14  is an exploded perspective of a lighting system according to an embodiment. 
     The lighting system according to the embodiment may include a cover  2100 , a light source module  2200 , a heat radiation member  2400 , a power supply unit  2600 , an internal case  2700 , and a socket  2800 . In addition, the lighting system according to the embodiment may further include at least one of a member  2300  and a holder  2500 . The light source module  2200  may include the light emitting device or the light emitting device package according to the embodiment. 
     The light source module  2200  may include a light source unit  2210 , a connection plate  2230 , and a connector  2250 . The member  2300  is provided on a top surface of the heat radiation member  2400 , and has a guide groove  2310  into which a plurality of light source units  2210  and the connector  2250  are inserted. 
     The holder  2500  closes a receiving groove  2719  of an insulating part  2710  provided in the internal case  2700 . Accordingly, the power supply unit  2600 , which is received in the insulating part  2710  of the internal case  2700 , is sealed. The holder  2500  has a guide protrusion part  2510 . 
     The power supply unit  2600  may include a protrusion part  2610 , a guide part  2630 , a base  2650 , and an extension part  2670 . The inner case  2700  may include a molding part together with the power supply unit  2600 . The molding part is formed by hardening a molding solution to fix the power supply unit  2600  to an inner part of the internal case  2700 . 
     A plurality of light emitting device packages according to the embodiment are arrayed on a substrate, and a light guide plate, a prism sheet, a diffusion sheet and a fluorescent sheet serving as optical members may be disposed on a path of light emitted from the light emitting device packages. 
     The light emitting device according to the embodiment may be applied to a backlight unit, a lighting unit, a display device, an indicator, a lamp, a street lamp, a vehicle lighting device, a vehicle display device, a smart clock, and the like, but the embodiment is not limited thereto. 
     Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.