Abstract:
The present disclosure relates to a III-nitride semiconductor light-emitting device including a substrate with a scattering zone formed therein, and a plurality of III-nitride semiconductor layers including a first III-nitride semiconductor layer formed over the substrate and having a first conductivity type, a second III-nitride semiconductor layer formed over the first III-nitride semiconductor layer and having a second conductivity type different from the first conductivity type, and an active layer disposed between the first III-nitride semiconductor layer and the second III-nitride semiconductor layer and generating light by recombination of electrons and holes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT Application No. PCT/KR2009/005707 filed on Oct. 7, 2009, which claims the benefit and priority to Korean Patent Application No. 10-2008-0104569, filed Oct. 24, 2008. The entire disclosures of the applications identified in this paragraph are incorporated herein by reference. 
       FIELD 
       [0002]    The present disclosure relates generally to a III-nitride semiconductor light-emitting device, and more particularly, to a III-nitride semiconductor light-emitting device which includes a substrate with a scattering zone formed therein to improve light extraction efficiency. The III-nitride semiconductor light-emitting device means a light-emitting device such as a light-emitting diode including a compound semiconductor layer composed of Al (x) Ga (y) In (1-x-y) N (0≦x1, 0≦y≦1, 0≦x+y≦1), and may further include a material composed of other group elements, such as SiC, SiN, SiCN and CN, and a semiconductor layer made of such materials. 
       BACKGROUND 
       [0003]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0004]      FIG. 1  is a view of an example of a conventional III-nitride semiconductor light-emitting device. The III-nitride semiconductor light-emitting device includes a substrate  100 , a buffer layer  200  grown on the substrate  100 , an n-type III-nitride semiconductor layer  300  grown on the buffer layer  200 , an active layer  400  grown on the n-type III-nitride semiconductor layer  300 , a p-type III-nitride semiconductor layer  500  grown on the active layer  400 , a p-side electrode  600  formed on the p-type III-nitride semiconductor layer  500 , a p-side bonding pad  700  formed on the p-side electrode  600 , an n-side electrode  800  formed on the n-type III-nitride semiconductor layer  300  exposed by mesa-etching the p-type III-nitride semiconductor layer  500  and the active layer  400 , and an optional protection film  900 . 
         [0005]    In the case of the substrate  100 , a GaN substrate can be used as a homo-substrate. A sapphire substrate, a SiC substrate or a Si substrate can be used as a hetero-substrate. However, any type of substrate that can have a nitride semiconductor layer grown thereon can be employed. In the case that the SiC substrate is used, the n-side electrode  800  can be formed on the surface of the SiC substrate. 
         [0006]    The nitride semiconductor layers epitaxially grown on the substrate  100  are usually grown by metal organic chemical vapor deposition (MOCVD). 
         [0007]    The buffer layer  200  serves to overcome differences in lattice constant and thermal expansion coefficient between the hetero-substrate  100  and the nitride semiconductor layers. U.S. Pat. No. 5,122,845 describes a technique of growing an AlN buffer layer with a thickness of 100 to 500 Å on a sapphire substrate at 380 to 800° C. In addition, U.S. Pat. No. 5,290,393 describes a technique of growing an Al (x) Ga (1-x) N (0≦x&lt;1) buffer layer with a thickness of 10 to 5000 Å on a sapphire substrate at 200 to 900° C. Moreover, U.S. Publication No. 2006/154454 describes a technique of growing a SiC buffer layer (seed layer) at 600 to 990° C., and growing an In (x) Ga (1-x) N (0&lt;x≦1) thereon. In particular, it is provided with an undoped GaN layer with a thickness of 1 micron to several microns (μm) on the AlN buffer layer, the Al (x) Ga (1-x) N (0≦x&lt;1) buffer layer or the SiC/In (x) Ga (1-x) N (0&lt;x≦1) layer, 
         [0008]    In the n-type nitride semiconductor layer  300 , at least the n-side electrode  800  formed region (n-type contact layer) is doped with a dopant. Some embodiments, the n-type contact layer is made of GaN and doped with Si. U.S. Pat. No. 5,733,796 describes a technique of doping an n-type contact layer at a target doping concentration by adjusting the mixture ratio of Si and other source materials. 
         [0009]    The active layer  400  generates light quanta by recombination of electrons and holes. For example, the active layer  400  contains In (x) Ga (1-x) N (0&lt;x≦1) and has a single layer or multi-quantum well layers. 
         [0010]    The p-type nitride semiconductor layer  500  is doped with an appropriate dopant such as Mg, and has p-type conductivity by an activation process. U.S. Pat. No. 5,247,533 describes a technique of activating a p-type nitride semiconductor layer by electron beam irradiation. Moreover, U.S. Pat. No. 5,306,662 describes a technique of activating a p-type nitride semiconductor layer by annealing over 400° C. U.S. Publication No. 2006/157714 describes a technique of endowing a p-type nitride semiconductor layer with p-type conductivity without an activation process, by using ammonia and a hydrazine-based source material together as a nitrogen precursor for growing the p-type nitride semiconductor layer. 
         [0011]    The p-side electrode  600  is provided to facilitate current supply to the p-type nitride semiconductor layer  500 . U.S. Pat. No. 5,563,422 describes a technique associated with a light-transmitting electrode composed of Ni and Au formed over almost the entire surface of the p-type nitride semiconductor layer  500  and in ohmic-contact with the p-type nitride semiconductor layer  500 . In addition, U.S. Pat. No. 6,515,306 describes a technique of forming an n-type superlattice layer on a p-type nitride semiconductor layer, and forming a light-transmitting electrode made of indium tin oxide (ITO) thereon. 
         [0012]    The p-side electrode  600  can be formed so thick as to not transmit but rather to reflect light toward the substrate  100 . This technique is called the flip chip technique. U.S. Pat. No. 6,194,743 describes a technique associated with an electrode structure including an Ag layer with a thickness over 20 nm, a diffusion barrier layer covering the Ag layer, and a bonding layer containing Au and Al, and covering the diffusion barrier layer. 
         [0013]    The p-side bonding pad  700  and the n-side electrode  800  are provided for current supply and external wire bonding. U.S. Pat. No. 5,563,422 describes a technique of forming an n-side electrode with Ti and Al. 
         [0014]    The optional protection film  900  can be made of SiO 2 . 
         [0015]    The n-type nitride semiconductor layer  300  or the p-type nitride semiconductor layer  500  can be constructed as a single layer or as plural layers. Vertical light-emitting devices are introduced by separating the substrate  100  from the nitride semiconductor layers using a laser technique or wet etching. 
         [0016]      FIG. 2  is a view of one example of a semiconductor light-emitting device described in U.S. Pat. No. 6,657,236. A rough surface  310  having a different refractive index is formed in a III-nitride semiconductor layer  300  to scatter light and thus to improve external quantum efficiency. 
         [0017]      FIG. 3  is a view of another example of the semiconductor light-emitting device described in U.S. Pat. No. 6,657,236. A material layer  120  (SiO 2  or nitride layer) with a different refractive index is formed on a substrate  100  with convex portions  110  formed thereon, and a III-nitride semiconductor layer  300  is formed on the resulting structure, thereby improving external quantum efficiency. 
         [0018]      FIG. 4  is a view of an example of a method for fabricating a semiconductor light-emitting device described in U.S. Pat. Publication No. 2008/121906. Grooves  130  are formed in a substrate  100  by a laser, and then grooves  140  are further formed in the substrate  100 . As such, the light-emitting device can be easily divided into individual chips. For example, the laser is irradiated from the opposite side of the substrate  100 , such as the groove  130 -formed side to the substrate  100 , and focused on the groove- 140 -to-be-formed region, thereby forming the grooves  140 . 
         [0019]      FIG. 5  is a view of an example of a method for fabricating a semiconductor light-emitting device described in Japanese Pat. Publication No. H11-163403. Grooves  130  are formed in a process-damaged layer  110  by laser irradiation. As such, the light-emitting device can be divided into individual chips. 
       SUMMARY 
       [0020]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0021]    There is provided a III-nitride semiconductor light-emitting device, including a substrate with a scattering zone formed therein; and a plurality of III-nitride semiconductor layers including a first III-nitride semiconductor layer formed over the substrate and having a first conductivity type, a second III-nitride semiconductor layer formed over the first III-nitride semiconductor layer and having a second conductivity type different from the first conductivity type, and an active layer disposed between the first III-nitride semiconductor layer and the second III-nitride semiconductor layer and generating light by recombination of electrons and holes. 
         [0022]    According to a III-nitride semiconductor light-emitting device of the present disclosure, light extraction efficiency of the light-emitting device can be improved. 
         [0023]    In an embodiment, according to a III-nitride semiconductor light-emitting device of the present disclosure, the scattering zone can be formed without any limitation on the order of the processes. 
         [0024]    In another embodiment, according to a III-nitride semiconductor light-emitting device of the present disclosure, light extraction efficiency of the light-emitting device can be improved by various scattering angles. 
         [0025]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0026]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0027]      FIG. 1  is a view of an example of a conventional III-nitride semiconductor light-emitting device. 
           [0028]      FIG. 2  is a view of one example of a semiconductor light-emitting device described in U.S. Pat. No. 6,657,236. 
           [0029]      FIG. 3  is a view of another example of the semiconductor light-emitting device described in U.S. Pat. No. 6,657,236. 
           [0030]      FIG. 4  is a view of an example of a method for fabricating a semiconductor light-emitting device described in U.S. Application No. 2008/121906. 
           [0031]      FIG. 5  is a view of an example of a method for fabricating a semiconductor light-emitting device described in Japanese Application No. 11-163403. 
           [0032]      FIG. 6  is a view of an embodiment of a III-nitride semiconductor light-emitting device according to the present disclosure. 
           [0033]      FIG. 7  is a view of one example of a substrate provided in the III-nitride semiconductor light-emitting device according to the present disclosure. 
           [0034]      FIG. 8  is a view of another example of the substrate provided in the III-nitride semiconductor light-emitting device according to the present disclosure. 
           [0035]      FIG. 9  is a view of a further example of the substrate provided in the III-nitride semiconductor light-emitting device according to the present disclosure. 
           [0036]      FIG. 10  is a view of an embodiment of a method for fabricating a III-nitride semiconductor light-emitting device according to the present disclosure. 
           [0037]      FIG. 11  is an SEM image of a substrate processed according to the present experimental example when viewed from the top. 
           [0038]      FIG. 12  is an SEM image of a substrate in which scattering zones are formed at given intervals according to the present experimental example when viewed from the top. 
           [0039]      FIG. 13  is an image of a III-nitride semiconductor light-emitting device including the substrate processed according to the present experimental example when viewed from the top. 
       
    
    
       [0040]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0041]    Hereinafter, the present disclosure will now be described in detail with reference to the accompanying drawings. 
         [0042]      FIG. 6  is a view of an embodiment of a III-nitride semiconductor light-emitting device according to the present disclosure. The III-nitride semiconductor light-emitting device includes a substrate  10 , a buffer layer  20  epitaxially grown on the substrate  10 , an n-type III-nitride semiconductor layer  30  epitaxially grown on the buffer layer  20 , an active layer  40  epitaxially grown on the n-type III-nitride semiconductor layer  30  and generating light by recombination of electrons and holes, a p-type III-nitride semiconductor layer  50  epitaxially grown on the active layer  40 , and a scattering zone  90 . 
         [0043]    The substrate  10  may be a sapphire substrate. 
         [0044]      FIG. 7  is a view of an example of the substrate provided in the III-nitride semiconductor light-emitting device according to the present disclosure. A scattering zone  90  is formed in the substrate  10  to scatter the light generated in the active layer  40  (referring to  FIG. 6 ). The scattering zone  90  is formed when an inner portion of the substrate  10  is transformed (e.g., when the sapphire of the sapphire substrate is transformed). Therefore, the scattering zone  90  can be formed in various sizes or shapes, and one scattering zone  90  can provide various scattering angles. The scattering zone  90  may be continuously formed by transversely or longitudinally crossing the space between the top and bottom surfaces of the substrate  10 . P represents an example of a light path. 
         [0045]      FIG. 8  is a view of another example of the substrate provided in the III-nitride semiconductor light-emitting device according to the present disclosure. A plurality of scattering zones  90  may be formed. The scattering zones  90  may be distributed irregularly or at given intervals. In some particular embodiments, the scattering zones  90  are formed at given intervals to evenly distribute the scattering zones  90 . P represents another example of a light path. 
         [0046]      FIG. 9  is a view of a further example of the substrate provided in the III-nitride semiconductor light-emitting device according to the present disclosure. Scattering zones  90  are continuously formed at given intervals by transversely crossing the space between the top and bottom surfaces of the substrate  10 . 
         [0047]    Hereinafter, a method for fabricating a III-nitride semiconductor light-emitting device according to the present disclosure will now be described using a sapphire substrate as an example. 
         [0048]      FIG. 10  is a view of an embodiment of the method for fabricating the III-nitride semiconductor light-emitting device according to the present disclosure. 
         [0049]    A substrate  10  is prepared (referring to  FIG. 10(   a )). 
         [0050]    A laser  88  is irradiated from a top surface  12  of the substrate  10  to the inside A of the substrate  12  in order to form a scattering zone  90  (referring to  FIG. 10(   b )). The laser  88  may be irradiated from a bottom surface  14  of the substrate  10 . The size, shape, and the like of the scattering zone  90  may be changed according to the irradiation conditions of the laser  88 . While the laser  88  is irradiated, the substrate  10  or the laser  88  is moved so that the scattering zone  90  can be continuously formed by transversely or longitudinally crossing the space between the top and bottom surfaces  12  and  14  of the substrate  10  (referring to  FIG. 10(   c )). For example, the laser  88  is focused on the inside A of the substrate  10 . When the light-emitting device is divided into individual light-emitting devices, the bottom surface  14  of the substrate  10  may be polished to reduce the thickness of the substrate  10  to allow easier dividing. In some embodiments, the laser  88  is focused on the inside A of the substrate  10  to be adjacent to the top surface  12  in order to prevent the scattering zone  90  from being damaged or destroyed when polished. 
         [0051]    A buffer layer  20 , an n-type III-nitride semiconductor layer  30 , an active layer  40 , and a p-type III-nitride semiconductor layer  50  are grown on the top surface  12  of the substrate  10  (referring to  FIG. 10(   d )). The scattering zone  90  may be formed after the buffer layer  20 , the n-type III-nitride semiconductor layer  30 , the active layer  40  and the p-type III-nitride semiconductor layer  50  are grown on the top surface  12  of the substrate  10 . 
       Experimental Example 
       [0052]      FIG. 11  is an SEM image of a substrate processed according to the present experimental example, when viewed from the top. A scattering zone  90  transformed by a laser was seen in the substrate  10 . A surface damage of the substrate  10  was not detected. 
         [0053]      FIG. 12  is an SEM image of a substrate wherein scattering zones are formed at given intervals according to the present experimental example when viewed from the top. The scattering zones  90  were formed in the substrate  10  at intervals I of 300 μm. 
         [0054]      FIG. 13  is an image of a III-nitride semiconductor light-emitting device including the substrate processed according to the present experimental example when viewed from the top. A scattering zone  90  formed in the substrate  10  (referring to  FIG. 6 ) scattered a large amount of light. 
         [0055]    The substrate  10  was a plane substrate formed of sapphire having a thickness of 400 μm and a diameter of 2 inches. 
         [0056]    A laser  88  was a UV pulse laser with a wavelength of 532 nm and a pulse of 7 ns. The laser  88  was focused at a depth of 130 μm from a top surface  12  of the substrate  10 . The substrate  10  was processed using a micro-spot lens. The laser  88  was irradiated to form the scattering zones  90  at intervals of 300 μm (referring to  FIGS. 10 to 12 ). 
         [0057]    Hereinafter, variety examples of the present invention are explained. 
         [0058]    (1) The III-nitride semiconductor light-emitting device wherein the scattering zone is a region formed by transformation of the substrate by a laser. 
         [0059]    (2) The III-nitride semiconductor light-emitting device wherein the scattering zone is continuously formed crossing the inside of the substrate. 
         [0060]    (3) The III-nitride semiconductor light-emitting device wherein the plurality of scattering zones are formed in the substrate. 
         [0061]    (4) The III-nitride semiconductor light-emitting device wherein the substrate is formed of sapphire. 
         [0062]    (5) The III-nitride semiconductor light-emitting device wherein the scattering zone is a region formed by transformation of the substrate by a laser. 
         [0063]    (6) The III-nitride semiconductor light-emitting device wherein the substrate is formed of sapphire, and the scattering zone is formed when the substrate is transformed by a laser, and is formed at an upper portion of the inside of the substrate 
         [0064]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention. 
         [0065]    The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.