Patent Publication Number: US-2019189850-A1

Title: Light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. provisional application No. 62/607,689 filed on Dec. 19, 2017, and the content of which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a light-emitting device, more particularly, to a light-emitting device with uniform current spreading and improved brightness. 
     Description of the Related Art 
     The light-emitting diodes (LEDs) of the solid-state lighting elements have the characteristics of low power consumption, low heat generation, long operation life, crash proof, small volume, quick response and good opto-electrical property like light emission with a stable wavelength, so the LEDs have been widely used in household appliances, indicator light of instruments, and opto-electrical products, etc. As the opto-electrical technology develops, the solid-state lighting elements have great progress in the light efficiency, operation life and the brightness, and LEDs are expected to become the main stream of the lighting devices in the near future. 
     A conventional LED basically includes a substrate, an n-type semiconductor layer, an active layer and a p-type semiconductor layer formed on the substrate, and p, n-electrodes respectively formed on the p-type/n-type semiconductor layers. When imposing a certain level of forward voltage to the LED via the electrodes, holes from the p-type semiconductor layer and electrons from the n-type semiconductor layer are combined in the active layer to generate light. However, the electrodes shelter light emitted from the active layer, and current may be crowded in semiconductor layers near the electrodes. Thus, optimized electrode and current blocking structures are needed for improving brightness, optical field uniformity and lowering an operating voltage of the LED. 
     SUMMARY OF THE DISCLOSURE 
     A light-emitting device, includes a substrate; a first semiconductor stack formed on the substrate, including a first semiconductor layer, a second semiconductor layer and an active layer formed therebetween; a first electrode formed on the first semiconductor layer; a second electrode formed on the second semiconductor layer, including a second pad electrode and a second finger electrode extending from the second pad electrode; a second current blocking region formed under the second electrode, including a second core region under the second pad electrode and a extending region under the second finger electrode; and a transparent conductive layer, formed on the second semiconductor layer and covering the extending region; wherein a contour of the second core region has a shape different from that of the second pad electrode; wherein the transparent conductive layer includes a first opening having a width wider than a width of the second pad electrode, wherein the second finger electrode includes a portion extending from the contour of the second pad electrode and having a width wider than other portion of the second finger electrode, and part of the portion is not covered by the transparent conductive layer. 
     A light-emitting device, includes a substrate; a first semiconductor stack formed on the substrate, including a first semiconductor layer, a second semiconductor layer and an active layer formed therebetween; an exposed region formed in the first semiconductor stack, including a side surface and a bottom including an upper surface of the first semiconductor layer; a first electrode formed in the exposed region and electrically connecting to the first semiconductor layer, including a first pad electrode and a first finger electrode extending from the first pad electrode; and a first current blocking region formed under the first electrode, including a plurality of islands under the first finger electrode; wherein a shortest distance between the side surface of the exposed region and one of the plurality of islands is not smaller than 1 μm. 
     A light-emitting device, includes a substrate; a first semiconductor stack formed on the substrate, including a first semiconductor layer, a second semiconductor layer and an active layer formed therebetween; an exposed region formed in the first semiconductor stack, including a bottom including an upper surface of the first semiconductor layer; a first electrode formed in the exposed region and electrically connecting to the first semiconductor layer, including a first pad electrode; and a first current blocking region formed under the first pad electrode; wherein the first pad electrode contacts an area of the upper surface of the first semiconductor layer outside of the first current blocking region; and wherein the first pad electrode includes a first side surface and the first current blocking region includes a second side surface, and wherein a slope of the first side surface is greater than a slope of the second side surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-2D  show a light-emitting device  1  in accordance with a first embodiment of the present application. 
         FIGS. 3A and 3B  respectively show a cross-sectional view taken along line C-C′ of the light-emitting device  1  in  FIG. 1 , in accordance with different embodiments of the present application. 
         FIGS. 4A-4C  show a light-emitting device  2  in accordance with a second embodiment of the present application. 
         FIGS. 5A and 5B  respectively show a cross-sectional view taken along line C-C′ of the light-emitting device  2  in  FIG. 4 , in accordance with different embodiments of the present application. 
         FIGS. 6A-6F  show a light-emitting device  3  in accordance with a third embodiment of the present application and the different embodiments of the light-emitting device  3 . 
         FIG. 6G  shows an enlarge view of partial areas of a light-emitting device in accordance with another embodiment of the present application. 
         FIGS. 7A-7D  show a light-emitting device  4  in accordance with a fourth embodiment of the present application. 
         FIGS. 8A-8B  respectively show a partial top view of the light-emitting device, in accordance with different embodiments 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. 
     First Embodiment 
       FIG. 1  shows a top view of a light-emitting device  1  in accordance with the first embodiment of the present application; FIG.  2 A shows a cross-sectional view taken along line A-A′ of the light-emitting device  1  in  FIG. 1 ;  FIG. 2B  shows a cross-sectional view taken along line B-B′ of the light-emitting device  1  in  FIG. 1 ;  FIG. 2C  shows an enlarged view of a partial area R 1  of the light-emitting device  1  in  FIG. 1 ; and  FIG. 2D  shows an enlarged view of a partial area R 2  of the light-emitting device  1  in  FIG. 1 . 
     As shown in  FIG. 1  and  FIGS. 2A-2C , the light-emitting device  1  includes a substrate  10 , a semiconductor stack  12  on the substrate  10 , a first and a second current blocking regions  40  and  50  on the semiconductor stack  12 , a transparent conductive layer  18  on the semiconductor stack  12 , a first electrode  20 , a second electrode  30 , and a protective layer (not shown) having openings to expose the first electrode  20  and the second electrode  30 . The first electrode  20  includes a first pad electrode  201  and one or more first finger electrodes  202 . The second electrode  30  includes a second pad electrode  301  and one or more second finger electrodes  302 . The first finger electrodes  202  extend from the first pad electrode  201  toward the second pad electrode  301 . The second finger electrodes  302  extend from the second pad electrode  301  toward the first pad electrode  201 . 
     In this embodiment, the second electrode  30  includes three second finger electrodes  302  extending from the second pad electrode  301 . The first electrode  20  includes two first finger electrodes  202  extending from the first pad electrode  201 . The first pad electrode  201  and the second pad electrode  301  are respectively disposed near two opposite edges of the light-emitting device  1 . One of the second finger electrodes  302  extends in a direction parallel with an edge between the two opposite edges of the light-emitting device  1  and is disposed between the two first finger electrodes  202 . The two first finger electrodes  202  are disposed between the second finger electrodes  302  respectively. 
     In another embodiment, the first electrode  20  and the second electrode  30  include less or more finger electrodes. 
     In another embodiment, one of the first electrode  20  and the second electrode  30  includes the pad electrode without finger electrode extending therefrom. 
     The substrate  10  can be a growth substrate, for example, gallium arsenide (GaAs) wafer for growing aluminum gallium indium phosphide (AlGaInP), sapphire (Al 2 O 3 ) wafer, gallium nitride (GaN) wafer or silicon carbide (SiC) wafer for growing indium gallium nitride (InGaN). The substrate  10  can be a patterned substrate with a patterned structure; i.e. the upper surface of the substrate  10  on which the semiconductor stack  12  is epitaxial grown can be patterned. Lights emitted from the semiconductor stack  12  can be refracted by the patterned structure of the substrate  10  so that the brightness of the LED is improved. Furthermore, the patterned structure retards or restrains the dislocation due to lattice mismatch between the substrate  10  and the semiconductor stack  12 , so that the epitaxy quality of the semiconductor stack  12  is improved. 
     In an embodiment of the present application, the semiconductor stack  12  can be formed on the substrate  10  by organic metal chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), hydride vapor deposition (HVPE), or ion plating, such as sputtering or evaporation. 
     The semiconductor stack  12  includes a first semiconductor layer  121 , an active layer  123  and a second semiconductor layer  122  sequentially formed on the substrate  10 . In an embodiment of the present application, the first semiconductor layer  121  and the second semiconductor layer  122 , such as a cladding layer or a confinement layer, have different conductivity types, electrical properties, polarities, or doping elements for providing electrons or holes. For example, the first semiconductor layer  121  is an n-type semiconductor, and the second semiconductor layer  122  is a p-type semiconductor. The active layer  123  is formed between the first semiconductor layer  121  and the second semiconductor layer  122 . The electrons and holes combine in the active layer  123  under a current driving to convert electric energy into light energy to emit a light. The wavelength of the light emitted from the light-emitting device  1  or the semiconductor stack  12  is adjusted by changing the physical and chemical composition of one or more layers in the semiconductor stack  12 . 
     The material of the semiconductor stack  12  includes a group III-V semiconductor material, such as Al x In y Ga (1-x-y) N or Al x In y Ga (1-x-y) P, wherein 0≤x, y≤ 1 ; (x+y)≤1. According to the material of the active layer, when the material of the semiconductor stack  12  is AlInGaP series material, red light having a wavelength between 610 nm and 650 nm or yellow light having a wavelength between 550 nm and 570 nm can be emitted. When the material of the semiconductor stack  12  is InGaN series material, blue or deep blue light having a wavelength between 400 nm and 490 nm or green light having a wavelength between 490 nm and 550 nm can be emitted. When the material of the semiconductor stack  12  is AlGaN series material, UV light having a wavelength between 400 nm and 250 nm can be emitted. The active layer  123  can be a single heterostructure (SH), a double heterostructure (DH), a double-side double heterostructure (DDH), or a multi-quantum well structure (MQW). The material of the active layer  123  can be i-type, p-type, or n-type semiconductor. 
     Besides, a buffer layer (not shown) is formed between the upper surface of the substrate  10  and the first semiconductor layer  121 . The buffer layer also reduces the lattice mismatch described above and restrains the dislocation so as to improve the epitaxy quality. The material of the buffer layer includes GaN, AlGaN or AlN. In one embodiment, the buffer layer includes a plurality of sub-layers (not shown). The sub-layers include the same material or different material. In one embodiment, the buffer layer includes two sub-layers. The sub-layers include same material AlN. The growth method of the first sub-layer of the two sub-layers is sputtering, and the growth method of the second sub-layers of the two sub-layers is MOCVD. In one embodiment the buffer layer further includes a third sub-layer. The growth method of the third sub-layers is MOCVD, and the growth temperature of the second sub-layer is higher than or lower than that of the third sub-layer. 
     An exposed region  28  is formed by etching and removing parts of the second semiconductor layer  122  and the active layer  123  downward to an upper surface of the first semiconductor layer  121 . The side surfaces of the second semiconductor layer  122  and the active layer  123  and the upper surface of the first semiconductor layer  121  are exposed. The first electrode  20  is disposed on the exposed upper surface of the first semiconductor layer  121  to form an electrical connection with the first semiconductor layer  121 . The second electrode  30  is disposed on the second semiconductor layer  122  to form an electrical connection with the second semiconductor layer  122 . 
     The first current blocking region  40  are formed between the first electrode  20  (the first pad electrode  201  and/or the first finger electrodes  202 ) and the first semiconductor layer  121 , and the second current blocking region  50  is formed between the second electrode  30  (the second pad electrode  301  and/or the second finger electrodes  302 ) and the second semiconductor layer  122 . Current is injected into the light-emitting device  1  via the first pad electrode  201  and the second pad electrode  301  and flows into the second finger electrodes  302 , and then spreads in the transparent conductive layer  18  and the second semiconductor layer  122 . The first current blocking region  40  and the second current blocking region  50  prevent most parts of the current from directly flowing into the active layer  123  under the electrodes. That is, the injected current is prevented from directly flowing downward at the electrode regions. 
     In the embodiment, as shown in  FIG. 1 , the first current blocking region  40  includes a first core region  401  under the first pad electrode  201  and a plurality of separated islands  402  under the first finger electrodes  202 . The second current blocking region  50  includes a second core region  501  under the second pad electrode  301 , and a plurality of extending regions  502  extending from the second core region  501  and under the second finger electrodes  302 . At regions of the first pad electrode  201  and the second pad electrode  301 , the current (electron or hole) is blocked from flowing downward via the first core region  401  and the second core region  501 . The current, spread in the first finger electrodes  202 , is blocked from flowing downward via the plurality of separated islands  402 , and flows into the first semiconductor layer  121  through regions between two adjacent islands  402 . The current, spread in the second finger electrodes  302  flows into the transparent conductive layer  18  and is blocked from flowing downward via the plurality of extending regions  502  under the second finger electrodes  302 , and then the current is spread laterally in the transparent conductive layer  18  and uniformly flow into the semiconductor stack  12 . 
     The material of the first and the second current blocking regions  40  and  50  includes transparent insulated material, such as silicon oxide, silicon nitride, silicon oxynitride, titanium oxide or aluminum oxide, etc. The structure of the current blocking region can be a single layer or alternately multiple layers, such as DBR (distributed Bragg reflector). The thickness of the first current blocking region  40  and the second current blocking region  50  ranges from 700-5000 Å. In one embodiment, the thickness of the first current blocking region  40  and the second current blocking region  50  ranges from 700-1000 Å. In another embodiment, the thickness of the first current blocking region  40  and the second current blocking region  50  ranges from 1000-5000 Å. 
     The transparent conductive layer  18  is formed on the second current blocking region  50  and the top surface of the second semiconductor layer  122 , so that the current injected into the second electrode  30  can be spread uniformly by the transparent conductive layer  18  and then flow into the second semiconductor layer  122 . Because the transparent conductive layer  18  is disposed on the light extraction side of the light-emitting device  1 , an electrically-conducting material that has transparent property is preferable to be selected. More specifically, the transparent conductive layer  18  may include thin metal film. The material of the thin metal film can be Ni or Au. The material of the transparent conductive layer  18  includes oxide containing at least one element selected from zinc, indium, or tin, such as ZnO (zinc oxide), InO (indium oxide), SnO (tin oxide), ITO (indium tin oxide), IZO (indium zinc oxide), or GZO (gallium-doped zinc oxide). 
     As shown in  FIG. 1 , the second current blocking region  50  has a larger area than that of the second electrode  30 . The extending region  502  of the second current blocking region  50  is disposed along the second finger electrodes  302  and has a width larger than that of the second finger electrodes  302 . The contour of the second current blocking region  50  exceeds the contour of the second electrode  30  by 1-10 μm. 
     The transparent conductive layer  18  includes an opening  180  exposing the second core region  501  of the second current blocking region  50 . In this embodiment, the width of the opening  180  of the transparent conductive layer  18  is smaller than the width of the second core region  501  and larger than the width of the second pad electrode  301 . The transparent conductive layer  18  covers the top surface of the second semiconductor layer  122 , the extending regions  502  of the second current blocking region  50  and partial top surface of the second core region  501 . Because the width of the opening  180  of the transparent conductive layer  18  is larger than the width of the second pad electrode  301 , the transparent conductive layer  18  does not contact the second pad electrode  301 . In one embodiment, as shown in  FIG. 2A , a distance D between an edge of the second core region  501  and the opening  180  ranges from 1 to 10 μm. Since the whole bottom area of the second pad electrode  301  contacts the second core region  501  of the second current blocking region  50 , and adhesion between the second pad electrode  301  and the second current blocking region  50  is stronger than that between the second pad electrode  301  and the transparent conductive layer  18 . The second pad electrode  301  is prevented from peeling off the light-emitting device  1 . The yield and reliability of the light-emitting device are improved. Furthermore, the transparent conductive layer  18  that does not contact the second pad electrode  301  can further prevent current directly flow into the second semiconductor layer  122  adjacent to the second pad electrode  301  via the contact between the transparent conductive layer  18  and the second pad electrode  301 . In other words, the light cannot be emitted by the semiconductor stack  12  adjacent to the second pad electrode  301 , and the current can be efficiently used. 
     As shown in  FIG. 2D , the enlarged view of the area R 2  of the light-emitting device  1 , the second finger electrode  302  includes a first portion  3021  extending from the periphery of the second pad electrode  301  and formed above the second current blocking region  50  and the transparent conductive layer  18 . The first portion  3021  extends beyond the opening  180  of the transparent conductive layer  18 . A part of the first portion  3021  is formed in the opening  180  of the transparent conductive layer  18  and connects another part of the first portion  3021  formed on the transparent conductive layer  18 . The width of the first portions  3021  is wider than other portion of the second finger electrode  302 . 
     As shown in  FIG. 1  an  FIG. 2A , The first core region  401  of the first current blocking region  40  has a larger area than that of the first pad electrode  201 . The contour of the first core region  401  exceeds the contour of the first pad electrode  201  by 3-15 μm. The plurality of separated islands  402  are disposed along the first finger electrodes  202 . Each island  402  has a width larger than that of the first finger electrodes  202 . As shown in  FIG. 2B , the island  402  does not contact the side surfaces of the second semiconductor layer  122  and the active layer  123  in the exposed region  28 . In one embodiment, a spacing S between the island  402  and the side surface of the exposed region  28  is not smaller than 1 μm. The plurality of separated islands  402  is distributed on the first semiconductor layer  121  and the first finger electrodes  202  only contact the first semiconductor layer  121  not covered by the islands  402 . Therefore, current is prevented from crowding in local region in the semiconductor stack  12  near the first core region  401 . Current spreading in the semiconductor stack  12  is improved. Besides, the islands  402  are composed of transparent insulated material and the side surfaces of the islands  402  are inclined in a cross sectional view. In this way, the side surfaces of the islands  402  benefit light extraction. Moreover, when the spacing S between the island  402  and the side surface of the exposed region  28  is not smaller than 1 μm, light will escape from the semiconductor stack  12  more easily. In one embodiment, the island  402  includes a round corner or round edge in a top view. The round corner or round edge of the island  402  is also helpful for light extraction. 
       FIG. 2C  shows an enlarged view of the partial area R 1  in the light-emitting device  1 . As shown in  FIG. 2C , the first finger electrode  202  includes a first portion  2021  extending from the periphery of the first pad electrode  201  and extending beyond the periphery of the current blocking region  401 . In other words, the first portion  2021  of the first finger electrode  202  is formed on a region of the first core region  401  near the periphery of the first core region  401  and a region of the first semiconductor layer  121 . One part of the first portion  2021  formed on the region of the first core region  401  includes a larger surface area than that of another part of the first portion  2021  formed on the region of the first semiconductor layer  121  from the top view of the light-emitting device  1  or the side view of the light-emitting device  1 . The width of the first portions  2021  is wider than other portion of the first finger electrode  202 . 
     The first portion  2021  of the first finger electrode  202  and the first portion  3021  of the second finger electrode  302  including wider widths and larger areas can allow higher current pass through to avoid electrostatic discharge (ESD) or Electrical Over Stress (EOS) damage. 
     As shown in  FIG. 2C , D 1  indicates the shortest distance between the first core region  401  and the island  402  which is most closed to the first core region  401  (i.e. the first island  402   a ), and D 2  indicates the shortest distance between two adjacent islands  402 . In this embodiment, D 1  is not greater than D 2 . 
     In one embodiment, the distance D 2  between each two adjacent islands  402  is substantially equal. In another embodiment, the distance between each two adjacent islands  402  increases as along the island  402  is disposed far away from the first pad electrode  201 . That is, while the island  402  is disposed more far away from the first pad electrode  201 , the distance between two adjacent islands  402  is greater. 
     In another embodiment, the total length of all the islands  402  under one first finger electrode  202  is L island  and the length of the one first finger electrode  202  is L finger ; the ratio L island /L finger  ranges from 20%-80%. 
     In another embodiment, an end of the first finger electrode  202  contacts the first semiconductor layer  121  without the islands  402  formed therebetween. 
     In another embodiment, the first finger electrode  202  and the second finger electrode  302  have different widths form a top view. For example, the first finger electrode  202  is wider than the second finger electrode  302 . 
     In another embodiment, the extending region  502  of the second current blocking region  50  and the island  402  of the first current blocking region  40  have different widths from a top view. For example, the extending region  502  of the second current blocking region  50  is wider than the island  402  of the first current blocking region  40 . 
       FIGS. 3A and 3B  respectively show cross-sectional views taken along line C-C′ of the light-emitting device  1  in  FIG. 1 , in accordance with different embodiments of the present application. The difference between the different embodiments and the first embodiment is the width of the opening  180  of the transparent conductive layer  18 . As shown in  FIG. 3A , the width of the opening  180  of the transparent conductive layer  18  is substantially equal to the width of the second core region  501 . The transparent conductive layer  18  does not contact the top surface of the second core region  501  of the second current blocking region  50 . As shown in  FIG. 3B , the width of the opening  180  of the transparent conductive layer  18  is larger than the width of the second core region  501 . The transparent conductive layer  18  neither contacts the top surface nor the side surface of the second core region  501 . 
     Second Embodiment 
       FIG. 4A  shows a top view of a light-emitting device  2  in accordance with the second embodiment of the present application.  FIG. 4B  shows a cross-sectional view taken along line C-C′ of the light-emitting device  2  in  FIG. 4A . The structure of the light-emitting device  2  is similar with that described in the first embodiment. The difference is, the second core region  502  of the second current blocking region  50  includes an opening  503  under the second pad electrode  301 . The second pad electrode  301  contacts the second semiconductor layer  122  via the opening  503 . The transparent conductive layer  18  covers the top surface of the second semiconductor layer  122 , the extending regions  502  of the second current blocking region  50  and a partial top surface of the second core region  501 . As shown in  FIG. 4B , the width W T  of the opening  180  of the transparent conductive layer  18  is smaller than the outer width W CB1  of the second core region  502  and greater than the width W CB2  of the opening  503  of the second core region  501  so that the transparent conductive layer  18  covers side surface and a partial top surface of the second core region  501 . Besides, W T  is larger than the width W P  of the second pad electrode  301  so that the transparent conductive layer  18  does not contact the second pad electrode  301 .  FIG. 4C  is an enlarged view of the partial region R 3  of  FIG. 4B . In one embodiment, a distance D between an outer edge of the second core region  501  and the opening  180  ranges from 1 to 10 μm. 
       FIGS. 5A and 5B  respectively show cross-sectional views taken along line C-C′ of the light-emitting device  2  in  FIG. 4A , in accordance with different embodiments of the present application. The difference between the different embodiments and the second embodiment is the width of the opening  180  of the transparent conductive layer  18 . As shown in  FIG. 5A , the width W T  of the opening  180  of the transparent conductive layer  18  is substantially equal to or larger than the width W CB1  of the second core region  501 . The transparent conductive layer  18  does not contact the top surface of the second core region  501 . As shown in  FIG. 5B , the width W P  of the second pad electrode  301  is not larger than or substantially equal to the width W CB2  of opening  503  of the second core region  501 . The second pad electrode  301  contacts neither the transparent conductive layer  18  nor the top surface of the second core region  501 . 
     In the embodiments shown in  FIGS. 5A and 5B , the whole bottom area of the second pad electrode  301  contacts the second core region  501  and/or the second semiconductor layer  122 , and adhesion between the second pad electrode  301  and the second current blocking region  50  ( 501 ) and/or the second semiconductor layer  122  is stronger than that between the second pad electrode  301  and the transparent conductive layer  18 , and then the second pad electrode is prevented from peeling off the light-emitting device. The yield and reliability of the light-emitting device are improved. 
     Third Embodiment 
       FIG. 6A  shows a top view of the light-emitting device  3  in accordance with the third embodiment of the present application.  FIG. 6B  shows an enlarged view of the partial region R 4  of  FIG. 6A .  FIG. 6C  shows a cross-sectional view taken along line B-B′ of the light-emitting device  3  in  FIG. 6A . 
     As shown in  FIG. 6A , the light-emitting device  3  includes a substrate  10 , a semiconductor stack  12  on the substrate  10 , a first and a second current blocking regions  40  and  50  on the semiconductor stack  12 , a transparent conductive layer  18  on the semiconductor stack  12 , a first electrode  20 , a second electrode  30 , and a protective layer (not shown) having openings to expose the first electrode  20  and the second electrode  30 . The structure of the light-emitting device  3  is similar with that described in the first embodiment. The differences between the light-emitting device  3  and the light-emitting device  1  are described as below. 
     In this embodiment, the second electrode  30  includes two second finger electrodes  302  extending from the second pad electrode  301 . The first electrode  20  includes one first finger electrode  202  extending from the first pad electrode  201 . The first pad electrode  201  and the second pad electrode  301  are disposed near two opposite edges of the light-emitting device  3 . The first finger electrode  202  extends in a direction parallel with an edge connecting the two opposite edges of the light-emitting device  3  and is disposed between the two second finger electrodes  302 . 
     The first current blocking region  40  includes a first core region  401  under the first pad electrode  201  and a plurality of separated islands  402  under the first finger electrode  202 . The second current blocking region  50  includes a second core region  501  under the second pad electrode  301  and a plurality of extending regions  502  extending from the second core region  501  and under the second finger electrodes  302 . 
     As shown in  FIG. 6C , the first core region  401  of the first current blocking region  40  has a width smaller than that of the first pad electrode  201 . Therefore, the first pad electrode  201  directly contacts an area of the first semiconductor layer  201  outside of the first core region  401 . The contour of the first pad electrode  201  exceeds the contour of the first core region  401  more than 2 μm. That is, a distance D between the edges of the first pad electrode  201  and the first core region  401  is more than 2 μm to assure a sufficient contact area between the first pad electrode  201  and the first semiconductor layer  121  for current injection. In one embodiment, D ranges from 2-15 μm. In the cross-sectional view, a slope of a side surface of the first pad electrode  201  is greater than a slope of a side surface of the first core region  401 . The gentler slope of a side surface of the first core region  401  can improve the yield and the reliability of the following process of the first pad electrode  201 . 
     The first core region  401  of the first current blocking region  40  below the first pad electrode  201  prevents the current from being directly injected into the semiconductor layer under the pad electrode, so that the current is forced to spread laterally. Another advantage that a light emitting device with a current blocking region is that light emitted from the active layer can be extract by the current blocking region and then brightness of the light emitting device can be improved. However, a larger blocking region means a less contact area between electrodes and the semiconductor stack, and then the electric characteristics might be affected, such as forward voltage (Vf) of the light emitting device. The area, position or layout of the current blocking region is a tradeoff according to brightness and electric characteristics of the light emitting device. As shown in the first embodiment, the light-emitting device has the semiconductor stack  12  with a larger area, and then a plurality of first finger electrodes  202  are chosen to satisfy the current spreading purpose in the semiconductor stack  12  with the larger area, and the first core region  401  which has a larger area than that of the first pad electrode  201  benefits brightness. As shown in the third embodiment, the light-emitting device  3  has the semiconductor stack  12  with smaller area and less first finger electrodes, for example, a single first finger electrode  202 , setting the first core region  401  to have an area smaller than that of the first pad electrode  201  increases the contact area between the first semiconductor layer  121  and the first electrode  20 , so that the forward voltage (Vf) can be decreased. 
     In one embodiment, the first core region  401  and the first pad electrode  201  have different shapes as shown in  FIG. 8A . In another embodiment, the first core region  401  and the first pad electrode  201  have similar shapes, and the first pad electrode  201  are rotated anticlockwise in several degrees, such as 30 degrees, as shown in  FIG. 8B . In  FIG. 8A  and  FIG. 8B , a part of the first core region  401  has a periphery beyond the periphery of the first pad electrode  201 , and another part of the first core region  401  has a periphery behind the periphery of the first pad electrode  201 . The part of the first core region  401  having the periphery beyond the periphery of the first pad electrode  201  can be a protrusion or plurality protrusions. The first pad electrode  201  partially contacts the first semiconductor layer  121  and current can be blocked by the part of the first core region  401  having a periphery beyond the periphery of the first pad electrode  201 . 
     As shown in  FIG. 6A , D 1  indicates the shortest distance between the first core region  401  and the island  402  which is most closed to the first core region  401 , and D 2  indicates the shortest distance between two adjacent islands  402 . In this embodiment, D 1  is not greater than D 2 . In one embodiment, D 1  is smaller than D 2 . 
     In this embodiment, as shown in  FIG. 6B , the second core region  501  and the second pad electrode  301  have different shapes in top view. That is, an outer contour of the second core region  501  and the second pad electrode  301  are not similar. For example, the second pad electrode  301  is a circle and the outer contour of the second core region  501  is an ellipse, square, rectangle, rounded rectangle as shown in  FIG. 6E , rhombus, trapezoid, polygon or any other shape with protrusions. In one embodiment, the distance between the outer contour of the second core region  501  and the second pad electrode  301  does not remain equal. For example, as shown in  FIG. 6B , the second pad electrode  301  is a circular shape and the second core region  501  is a polygonal shape. A first part of the contour of the second core region  501 , i.e. the part which faces the first electrode  20 , is an arc. A second part of the contour of the second core region  501 , i.e. the part which is distant from the first electrode  20 , has a periphery of a part of a rectangle composed by three lines. A distance between the first part of contour of the second core region  501  and the second pad electrode  301  is D 3 , and a distance between the second part of contour of the second core region  501  and the second pad electrode  301  is D 4 . D 3  is smaller than D 4 . As a result, a current blocking region at the side facing the first electrode  20  is smaller than that at the side distant from the first electrode  20 . The efficient light emission region of the semiconductor stack  12  is between the first electrode  20  and second electrode  30  caused by current spreading between the first electrode  20  and second electrode  30 . In order to block current flowing to regions not between the first electrode  20  and second electrode  30 , especially the region between the second pad electrode  301  and the adjacent edge of the light-emitting device  3 , the second core region  501  between the second pad electrode  301  and the adjacent edge of the light-emitting device  3  includes a larger area than that of the second core region  501  at the side facing the first electrode  20 . Current from the second pad electrode  301  tends to flow toward the first electrode  20  more easily. 
     In another embodiment, the second extending region  502  and the second finger electrode  302  have different shapes in top view. 
       FIGS. 6D-6F  respectively show different designs for the second electrode  30  and the second blocking region  50 , in accordance with different embodiments of the present application. In  FIGS. 6D and 6E , D 3  is smaller than D 4 . 
     In one embodiment, the second core region  501  of the second current blocking region  50  includes an opening (not shown) exposing the second semiconductor layer  122 , as described in the second embodiment. In one embodiment, the opening of the second core region  501  has a shape the same as the shape of the second core region  501 . For example, a shape of the second core region  501  is a circle as shown in  FIG. 6D , and a shape of the opening of the second core region  501  is also a circle. In one embodiment, the opening of the second core region  501  has a shape different from the shape of the second core region  501 . For example, a shape of the second core region  501  is a rounded rectangle as shown in  FIG. 6F , and a shape of the opening of the second core region  501  is a circle (not shown). 
       FIG. 6G  shows an enlarged view of partial areas of the second electrode  30  and the second current blocking region  50  of a light-emitting device in accordance with another embodiment of the present application. The structure of the light-emitting device in  FIG. 6G  is similar to that of the light-emitting device  3 . The differences between the light-emitting device in  FIG. 6G  and the light-emitting device  3  are electrode layout and the second current blocking region  50 . As shown in  FIG. 6G , the second core region  501  ( 501   a ) and the second pad electrode  301  have different shapes in top view. The second core region  501  of the second current blocking region  50  includes a plurality of islands  501   a  separated with each other by slits  504 . The transparent conductive layer  18  covers the extending region  502  and parts of the second core region  501  of the second current blocking region  50  and includes an opening  180  exposing a portion of top surfaces of the islands  501   a.  The second pad electrode  301  is formed on the plurality of islands  501   a  and contacts the second semiconductor layer  122  via the slits  504 . In one embodiment, the extending region  502  of the second current blocking region  50  connects to one of the island  501   a  as shown in  FIG. 6G . In another embodiment, the extending region  502  of the second current blocking region  50  is divided from the second core region  501 . 
     Fourth Embodiment 
       FIGS. 7A-7D  show a light-emitting device  4  in accordance to a fourth embodiment of the present application. In the embodiment, the light-emitting device  4  is a light-emitting diode array.  FIG. 7A  shows a top view of the light-emitting device  4 .  FIG. 7B  and  FIG. 7C  respectively show cross-sectional views taken along line B-B′ and line C-C′ of the top view in  FIG. 7A .  FIG. 7D  shows an enlarged view of a partial area R of the top view in  FIG. 7A . 
     The light-emitting device  4  includes a substrate  10  and a plurality of light-emitting units  22  ( 22   a - 22   f ) formed on the substrate  10  and arranged in a two-dimensional array. Each light-emitting unit  22  includes a semiconductor stack  12 . The plurality of light-emitting units  22  electrically connects in series via connecting electrodes  60 , first finger electrodes  202  and second finger electrodes  302  formed thereon. 
     The manufacturing method of the light-emitting device  4  is described as below. The semiconductor stack  12  is formed on a substrate  10  by epitaxy process. Then, as shown in  FIG. 7B  and  FIG. 7C , a portion of the semiconductor stack  12  is selectively removed by etching process to expose the first surface  101  of the substrate  10 . The exposed first surfaces  101  and the side surfaces between the adjacent semiconductor stacks  12  form trenches  36  so that the plurality of semiconductor stacks  12  of the light-emitting units  22  are separately arranged on the substrate  10 . An exposed regions  28  of each light-emitting unit  22  is formed by photolithography and etching process so that the exposed region  28  serves as a platform for forming pads for connecting outside power providing current or other electronic components, or forming electrodes which spread the injected current and/or electrically connect the adjacent units thereon. 
     In another embodiment, in order to increase light-extraction efficiency or heat dispersion efficiency of the light-emitting device, the semiconductor stack  12  of the light-emitting unit  22  can be disposed on the substrate  10  by wafer transferring and wafer bonding. The wafer bonding method includes direct bonding or indirect bonding. Direct bonding can be fusion bonding or anodic bonding, etc. In indirect bonding, the semiconductor stack  12  of the light-emitting unit  22  is epitaxial grown on an epitaxial substrate (not shown), and then is bonded with the substrate  10  by adhering, heating or pressuring. The semiconductor stack  12  of the light-emitting unit  22  can be adhered to the substrate  10  by an inter-medium (not shown). The inter-medium can be a transparent adhesion layer, and it also can be replaced by a metal material. The transparent adhesion layer can be organic polymer transparent glue, such as polyimide, BCB (Benzocyclobutene), PFCB (Perfluorocyclobutyl), Epoxy, Acrylic resin, PET (Polyethylene terephthalate), PC (Polycarbonate) or combination thereof; or a transparent conductive oxide metal such as ITO, InO, SnO 2 , ZnO, FTO (fluorine-doped tin oxide), ATO (antimony tin oxide), CTO (cadmium tin oxide), AZO (aluminum-doped zinc-oxide), GZO (gallium-doped zinc oxide) or combination thereof; or an inorganic insulator, such as SOG (spin-on-glass), Al 2 O 3 , SiN x , SiO 2 , AlN, TiO 2 , Ta 2 O 5  or combination thereof. The metal material includes but is not limited to Au, Sn, In, Ge, Zn, Be, Pd, Cr, or alloy thereof such as PbSn, AuGe, AuBe, AuSn, PdIn, etc. 
     In fact, the method of forming the semiconductor stack  12  of the light-emitting unit  22  on the substrate  10  is not limited to these approaches. People having ordinary skill in the art can understand that the semiconductor stack  12  of the light-emitting unit  22  can be directly epitaxial grown on the substrate  10  according to different characteristics of the structures, such as optical and electrical properties, or productivity. 
     Next, an insulator  23  is disposed on the trenches  36  and continuously covers side surfaces and top surfaces of the semiconductor stack  12  of the light-emitting units  22 . The insulator  23  includes a middle structure  23   a  covering a portion or all of the trench  36  between two adjacent light-emitting units  22 . Parts of the insulator  23  which covers the top surface of the second semiconductor layer  122  is patterned to form a second core region  501  and extending regions  502  of the second current blocking region  50  as described in the above embodiments. The extending regions  502  connect to the middle structure  23   a.  Parts of the insulator  23  on the first semiconductor layer  121  is further patterned to form a first core region  401  and a plurality of separated islands  402  of the first current blocking region  40  as described in the above embodiments. The islands  402  are separated from the middle structure  23   a.  The functions of the plurality of separated islands  402  of the first current blocking region  40  and the extending region  502  of the second current blocking region  50  are the same as described in the above embodiments. The middle structure  23   a  of the insulator  23  formed in the trenches  36  and on the side surfaces of the light-emitting units  22  protects the semiconductor stacks  12  and electrically insulates the adjacent light-emitting units  22 . The material of the insulator  23  includes transparent insulated material, such as silicon oxide, silicon nitride, silicon oxynitride, titanium oxide or aluminum oxide. 
     In one embodiment, the structures of the insulator  23  (the middle structure  23   a,  the second current blocking region  50  or the first current blocking region  40 ) can be a single layer or alternately multiple layers, such as DBR (distributed Bragg reflector). 
     In another embodiment, the plurality of separated islands  402  of the first current blocking region  40  is omitted. 
     In another embodiment, the first core region  401  of the first current blocking region  40  is omitted. 
     Then, the transparent conductive layer  18  is disposed on the second semiconductor layer  122  and covers the extending regions  502  of the second current blocking region  50 . The transparent conductive layer  18  includes an opening  180  on the light-emitting unit  22   a  exposing the second core region  502 . The material of the transparent conductive layer  18  includes a metal oxide material such as indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide (ATO), indium zinc oxide (IZO), aluminum-doped zinc oxide (AZO), or zinc tin oxide (ZTO). A metal layer with a thickness that light can pass through also can be the transparent conductive layer  18 . 
     Next, an electrode layer is formed on the light-emitting units  22  and the trenches  36 . The electrode layer includes the first pad electrode  201  on the light-emitting units  22   f,  the second pad electrode  301  on the light-emitting units  22   a,  first finger electrodes  202  and second finger electrodes  302  formed on the light-emitting units  22   a - 22   f,  and connecting electrodes  60  formed between two adjacent light-emitting units  22  ( 22   a  and  22   b,    22   b  and  22   c,    22   c  and  22   d,    22   d  and  22   e,    22   e  and  22   f ). Each of the connecting electrodes  60  is formed on the trench  36  and connects the first finger electrode  202  on one light-emitting unit and the second finger electrodes  302  on the adjacent light-emitting units  22 . Each connecting electrode  60  connecting the first finger electrode  202  and the second finger electrodes  302  electrically connects two adjacent light-emitting units  22  so that the light-emitting units  22  form a series light-emitting diode array. In the present embodiment, a width of each connecting electrode  60  is larger than that of the first finger electrodes  202  and the second finger electrodes  302  in top view. 
     As shown in  FIG. 7D , the connecting electrode  60  includes tapered structures  601  linked to the first finger electrode  202  and the second finger electrode  302 . As shown in  FIGS. 7B and 7C , the connecting electrode  60  is formed on the insulator  23  in the trench  36  and covers the side surfaces and a part of the top surfaces of the two adjacent light-emitting units  22 . The thickness of the connecting electrode  60  on the side surface of the light-emitting units  22  is smaller than that of the first finger electrodes  202  and/or the second finger electrodes  302 . The connecting electrode  60  includes a width less than that of the middle structure  23   a  of the insulators  23  formed thereunder and larger than that of the first finger electrode  202  and/or the second finger electrode  302 . In on embodiment, a part of the side surfaces of the light-emitting units  22  where the connecting electrodes  60  are formed on can have a slope gentler than slopes of other parts of the side surfaces of the light-emitting units  22 . In another embodiment, the method of electrically connecting two adjacent light-emitting units  22  is not limited to what is described above. People having ordinary skill in the art can understand that connecting electrodes  60  may link first finger electrodes  202  or second finger electrodes  302  disposed on the semiconductor layers with same conductivity or different conductivity of the different light-emitting units  22 , so that the light-emitting units  22  can be electrically connected in series or in parallel. 
     The structures of the first electrode  20 , the first current blocking region  40 , the second electrode  30 , the transparent conductive layer  18  and the second current blocking region  50  described in the above embodiments can be applied in the light-emitting device  4 . More specifically, the structures of the first pad electrode  201 , the first core region  401  of the first current blocking region  40 , the second pad electrode  301 , the transparent conductive layer  18  and the second core region  501  of the second current blocking region  50  described in the above embodiments can be applied in the light-emitting device  4 . For example, as shown in  FIG. 7B , the width of the opening  180  of the transparent conductive layer  18  is smaller than the width of the second core region  501  and larger than the width of the second pad electrode  301 . The transparent conductive layer  18  covers the top surface of the second semiconductor layer  122 , the extending regions  502  of the second current blocking region  50  and a partial top surface of the second core region  501 . Because the width of the opening  180  of the transparent conductive layer  18  is larger than the width of the second pad electrode  301 , the transparent conductive layer  18  does not contact the second pad electrode  301 . 
     Referring to  FIG. 7C , the first core region  401  of the first current blocking region  40  is formed under the first pad electrode  201 . The first core region  401  of the first current blocking region  40  has a width smaller than that of the first pad electrode  201 . Therefore, the first pad electrode  201  directly contacts an area of the first semiconductor layer  201  outside of the first core region  401 . In one embodiment, a slope of a side surface of the first pad electrode  201  is greater than a slope of a side surface of the first core region  401 . The gentler slope of a side surface of the first core region  401  can improve the yield and the reliability of the following process of the first pad electrode  201 . 
     As shown in  FIG. 7D , D 1  indicates the shortest distance between the middle structure  23   a  of the insulator  23  under the connecting electrode  60  and the island  402  of the first current clocking region  40  which is closest to the trench  36 , and D 2  indicates the shortest distance between two adjacent islands  402 . In this embodiment, D 1  is not greater than D 2 . In one embodiment, D 1  is smaller than D 2 . In one embodiment, the island  402  is disposed under the first finger electrode  202  but not covered by the connecting electrode  60 . In another embodiment, as shown in  FIG. 7D , the islands  402  which is closest to the trench  36  extends to the tapered structure  601  of the connecting electrode  60 . A part or parts of the islands  402  closest to the trench  36  is formed under the tapered structure  601 . 
     The middle part  23   a  of the insulator  23  under the connecting electrode  60  has a width W larger than that of the connecting electrode  60 . In one embodiment, W is larger than twice of the maximum width of the connecting electrode  60 . 
     In one embodiment, a width of the middle structure  23   a  that exceeds the connecting electrode  60  is larger than a width of the extending region  502  of the second current blocking region  50  that exceeds the second finger electrode  302 . 
     In another embodiment, one end of the middle part  23   a  of the insulator  23  connects to the extending region  502  of the second current blocking region  50  of one light-emitting unit  22 , and the other end of the middle part  23   a  does not cover the side surface of the first semiconductor layer  121  of the adjacent light-emitting unit  22 . The side surface of the first semiconductor layer  121  is exposed, and the connecting electrode  60  contacts the side surface of the first semiconductor layer  121  via the exposed side surface of the first semiconductor layer  121 . 
     In another embodiment, the thickness of the middle part  23   a  of the insulator  23  on the side surface of each light-emitting unit  22  is smaller than that of the island  402  of the first current blocking region  40  and/or that of the extending region  502  of the second current blocking region  50 . 
     In another embodiment, the first finger electrode  202  and the second finger electrode  302  have different widths from a top view. For example, the first finger electrode  202  is wider than the second finger electrode  302 . 
     In another embodiment, the extending region  502  of the second current blocking region  50  and the island  402  of the first current blocking region  40  have different widths from a top view. For example, the extending region  502  of the second current blocking region  50  is wider than the island  402  of the first current blocking region  40 . 
     The material of the first pad electrode  201 , the first finger electrodes  202 , the second pad electrode  301 , the second finger electrodes  302  and the connecting electrodes  60  are preferably metal, such as Au, Ag, Cu, Cr, Al, Pt, Ni, Ti, Sn, Rh, alloy or stacked composition of the materials described above. 
     The light-emitting unit  22   a  can be the start unit of the electrical series and the light-emitting unit  22   f  can be the end unit of the electrical series. The light-emitting device  4  electrically connects to an external power or other circuits by wiring or soldering the first pad electrode  201  and the second pad electrode  301 . 
     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 disclosure covers modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.