Abstract:
The present disclosure relates to a III-nitride semiconductor light-emitting device including a substrate, a plurality of III-nitride semiconductor layers positioned on the substrate and including an active layer which generates light by recombination of electrons and holes, and a surface scattering the light generated in the active layer, the scattering surface including a first surface which is etched and a second surface which caps the first surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT Application No. PCT/KR2009/005706 filed on Sep. 7, 2009, which claims the benefit and priority to Korean Patent Application No. 10-2008-0101155, filed Oct. 15, 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 with an air-void formed therein to substantially function as a scattering surface. 
         [0003]    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≦x≦1, 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 
       [0004]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0005]      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 a protection film  900 . 
         [0006]    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. 
         [0007]    The nitride semiconductor layers epitaxially grown on the substrate  100  are grown usually by metal organic chemical vapor deposition (MOCVD). 
         [0008]    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, there 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. 
         [0009]    In the n-type III-nitride semiconductor layer  300 , at least the n-side electrode  800  region (n-type contact layer) is doped with a dopant. In 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 ratio of Si and other source materials in the mixture. 
         [0010]    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. 
         [0011]    The p-type III-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 III-nitride semiconductor layer by electron beam irradiation. Moreover, U.S. Pat. No. 5,306,662 describes a technique of activating a p-type III-nitride semiconductor layer by annealing over 400° C. U.S. Publication No. 2006/157714 describes a technique of endowing a p-type III-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 III-nitride semiconductor layer. 
         [0012]    The p-side electrode  600  is provided to facilitate current supply to the p-type III-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 and formed almost on the entire surface of the p-type III-nitride semiconductor layer  500  and in ohmic-contact with the p-type III-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 III-nitride semiconductor layer, and forming a light-transmitting electrode made of indium tin oxide (ITO) thereon. 
         [0013]    Meanwhile, the p-side electrode  600  can be formed thick so as to not transmit but rather to reflect light toward the substrate  100 . This technique is called the flip chip technique. For example, 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, a bonding layer containing Au and Al, and covering the diffusion barrier layer. 
         [0014]    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. 
         [0015]    The optional protection film  900  can be made of SiO 2 . 
         [0016]    In the meantime, the n-type III-nitride semiconductor layer  300  or the p-type III-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 III-nitride semiconductor layers using a laser technique or wet etching. 
         [0017]    A technique for forming patterns on the substrate  100  is used before growing the III-nitride semiconductor layer on the substrate  100 , thereby reducing crystal defects of the III-nitride semiconductor layer or improving external quantum efficiency of the light-emitting device. 
         [0018]      FIG. 2  is a view of an example of light-emitting devices described in U.S. Pat. Nos. 6,335,546 and 7,115,486. III-nitride semiconductor layers  200  and  300  are laterally epitaxially grown on a substrate  100  with the protrusion  110  formed thereon, thereby reducing crystal defects. As the III-nitride semiconductor layers  200  and  300  are laterally grown, cavities  120  (voids or air-voids) are formed on the substrate  100 . 
         [0019]      FIG. 3  is a view of an example of light-emitting devices described in U.S. Pat. Nos. 6,870,190 and 7,053,420. A III-nitride semiconductor layer  300  is grown on a substrate  100  with patterns formed thereon. The III-nitride semiconductor layers  300  are grown on the bottom surface and the protrusion of the patterned substrate  100 , and then brought into contact with each other. The growth of the III-nitride semiconductor layer  300  is facilitated in the contact regions thereof. As such, the III-nitride semiconductor layer  300  has a flat surface. The use of the patterned substrate  100  can scatter light to improve external quantum efficiency and can reduce crystal defects to improve quality of the III-nitride semiconductor layer  300 . 
         [0020]      FIG. 4  is a view of an example of light-emitting devices described in U.S. Pat. No. 6,870,191 and U.S. Publication No. 2005/082546. A III-nitride semiconductor layer  300  is grown on a substrate  100  with the protrusion  110  formed thereon, the protrusion  110  having a circular vertical section (or non-flat top surfaces). Since the III-nitride semiconductor layer  300  is grown merely on the bottom surface of the substrate  100 , it can be rapidly grown. 
         [0021]      FIG. 5  is a view of an example of a light-emitting device described in U.S. Pat. No. 6,657,236. As a III-nitride semiconductor layer  300  is grown on a mask  130  such as SiO 2 , cavities  120  are formed. The cavities  120  scatter light in the light-emitting device, thereby improving external quantum efficiency of the light-emitting device. 
         [0022]      FIG. 6  is a view of an example of light-emitting devices described in U.S. Pat. Nos. 5,491,350 and 6,657,236. As a III-nitride semiconductor layer  300  is grown on a substrate  100  with surface patterns formed on the bottom, cavities  120  are formed in the substrate  100 . The cavities  120  scatter light in the light-emitting device, thereby improving external quantum efficiency of the light-emitting device. 
         [0023]    However, unlike the cavity  120  of  FIG. 5 , the cavity  120  of  FIG. 6  has a small curvature on the interface with the III-nitride semiconductor layer  300 . Therefore, its scattering effect is not significant. 
       SUMMARY 
       [0024]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0025]    There is provided herein a III-nitride semiconductor light-emitting device, including: a substrate; a plurality of III-nitride semiconductor layers positioned on the substrate and including an active layer which generates light by recombination of electrons and holes; and a surface scattering the light generated in the active layer, the scattering surface including a first surface which is etched and a second surface which caps the first surface. 
         [0026]    There is also provided herein a method for fabricating a III-nitride semiconductor light-emitting device, including: a substrate; a plurality of III-nitride semiconductor layers positioned on the substrate and including an active layer which generates light by recombination of electrons and holes; and a surface scattering the light generated in the active layer, the scattering surface including a first surface which is etched and a second surface which caps the first surface. 
         [0027]    According to a III-nitride semiconductor light-emitting device of the present disclosure, external quantum efficiency can be improved, for example, by using a cavity having a large curvature. 
         [0028]    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 
         [0029]    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. 
           [0030]      FIG. 1  is a view of an example of a conventional III-nitride semiconductor light-emitting device. 
           [0031]      FIG. 2  is a view of an example of light-emitting devices described in U.S. Pat. Nos. 6,335,546 and 7,115,486. 
           [0032]      FIG. 3  is a view of an example of light-emitting devices described in U.S. Pat. Nos. 6,870,190 and 7,053,420. 
           [0033]      FIG. 4  is a view of an example of light-emitting devices described in U.S. Pat. No. 6,870,191 and U.S. Publication No. 2005/082546. 
           [0034]      FIG. 5  is a view of an example of a light-emitting device described in U.S. Pat. No. 6,657,236. 
           [0035]      FIG. 6  is a view of an example of light-emitting devices described in U.S. Pat. Nos. 5,491,350 and 6,657,236. 
           [0036]      FIG. 7  is a view of an embodiment of a III-nitride semiconductor light-emitting device according to the present disclosure. 
           [0037]      FIG. 8  is a view of an embodiment of a method for fabricating a III-nitride semiconductor light-emitting device according to the present disclosure. 
           [0038]      FIG. 9  is a scanning electron microscope (SEM) image of a substrate obtained after the growth of a primary III-nitride semiconductor layer, when viewed from the top. 
           [0039]      FIG. 10  is a sectional SEM image obtained after etching. 
           [0040]      FIG. 11  is a sectional SEM image obtained after growth of a secondary III-nitride semiconductor layer. 
       
    
    
       [0041]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0042]    Hereinafter, the present disclosure will now be described in detail with reference to the accompanying drawings. 
         [0043]      FIG. 7  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  grown on the substrate  10 , an n-type III-nitride semiconductor layer  30  grown on the buffer layer  20 , an active layer  40  grown on the n-type III-nitride semiconductor layer  30 , a p-type III-nitride semiconductor layer  50  grown on the active layer  40 , a p-side electrode  60  formed on the p-type III-nitride semiconductor layer  50 , a p-side bonding pad  70  formed on the p-side electrode  60 , and an n-side electrode  80  formed on the n-type III-nitride semiconductor layer  30  exposed by mesa-etching the p-type III-nitride semiconductor layer  50  and the active layer  40 . Moreover, circular protrusion  11  can be formed over the substrate  10 , processed scattering surfaces  31  can be formed at the lower portion of the n-type III-nitride semiconductor layer  30 , and cavities  12  can be formed between the protrusion  11  and the processed scattering surfaces  31 , respectively. Therefore, according to the III-nitride semiconductor light-emitting device of the present disclosure, external quantum efficiency of the light-emitting device is improved by the processed scattering surface  31  formed between the III-nitride semiconductor layer and the cavity  12  having different refractive indexes, and by the protrusion  11  formed between the cavity  12  and the substrate  10  having different refractive indexes. 
         [0044]      FIG. 8  is a view of an embodiment of a method for fabricating a III-nitride semiconductor light-emitting device according to the present disclosure. First, a substrate  10  with the protrusion  11  formed thereon is prepared. Here, the protrusion  11  may be formed by etching the substrate  10  or formed of a material different from the substrate  10 , such as SiO 2 . 
         [0045]    Next, a primary III-nitride semiconductor layer A is formed on the substrate  10  with the protrusion  11  formed thereon. Here, upper parts of the protrusion  11  are exposed. In this respect, protrusion  11  can be any shape. For example, protrusion  11  can have a circular or a pointed vertical section (i.e., non-flat upper parts) to prevent the primary III-nitride semiconductor layer A from being grown on the protrusion  11 . In particular, when the protrusions  11  having a height of 1.2 μm and a bottom diameter of 3 μm are formed on a (0001) sapphire substrate at intervals of 1 μm, a primary III-nitride semiconductor layer A can be grown using a 30-nm buffer layer and 2-μm undoped GaN. When the undoped GaN is grown on the (0001) sapphire substrate, the primary III-nitride semiconductor layer A is formed with {10-11} surfaces A 1  exposed. Accordingly, the primary III-nitride semiconductor layer A has holes formed by the {10-11} surfaces on the protrusion  11  (referring to  FIG. 9 ). 
         [0046]    Next, etching spaces  15  can be defined between the protrusion  11  and the primary III-nitride semiconductor layer A. The etching may be performed using, for example, a high-temperature mixed solution of phosphoric acid and sulfuric acid, a high-temperature KOH solution, high-temperature oxalic acid [(COOH) 2 ], or the like. The etching is rapidly performed on the interface between the protrusion  11  and the primary III-nitride semiconductor layer A having poor crystal quality, thereby defining the space  15 . Here, the shape, thickness, and the like of the spaces  15  may be influenced by the etching conditions and the shape of the protrusion  11 . 
         [0047]      FIG. 10  is a sectional SEM image obtained after an etching. The etching was performed at 250° C. for 15 sec. using a mixed solution of phosphoric acid and sulfuric acid (3:1). The space  15  was formed between the protrusion  11  and the primary III-nitride semiconductor layer A. A {10-11} crystal surface A 2  having a relatively low etching rate was exposed by etching. 
         [0048]    Finally, a secondary III-nitride semiconductor layer B can be formed. During this process, the spaces  15  are capped by the lateral growth mode of the secondary III-nitride semiconductor layer B, thereby forming closed cavities  12 . The secondary III-nitride semiconductor layer B may be formed by further growing undoped GaN (e.g., 2 μm) and then growing the n-type III-nitride semiconductor layer  30 , the active layer  40 , and the p-type III-nitride semiconductor layer  50  on the undoped GaN, as shown in  FIG. 7 . 
         [0049]      FIG. 11  is a sectional SEM image obtained after the growth of the secondary III-nitride semiconductor layer B. It can be known that the cavity  12  has been formed well, surrounded by the protrusion  11 , the primary III-nitride semiconductor layer A and the secondary III-nitride semiconductor layer B. The processed scattering surface  31  (referring to  FIG. 7 ) includes an etched surface  31   a  and a capping surface  31   b  formed by the epitaxial growth. 
         [0050]    Hereinafter, variety embodiments of the present disclosure are explained. 
         [0051]    (1) The III-nitride semiconductor light-emitting device comprising a protrusion disposed between a closed scattering surface and a substrate. 
         [0052]    (2) The III-nitride semiconductor light-emitting device wherein a scattering surface is convex over the protrusion. 
         [0053]    The III-nitride semiconductor light-emitting device further comprising a protrusion disposed below a cavity defined by an etching and formed of a material different from that of a substrate. For example, when the protrusions formed of silicon oxide, such as SiO 2 , growth does not occur thereon. Therefore, although a protrusion having a flat upper part is used, the upper part of the protrusion may remain exposed during the growth of a III-nitride semiconductor layer. 
         [0054]    (4) The III-nitride semiconductor light-emitting device further comprising a scattering surface including a cover layer formed of a III-nitride semiconductor layer. 
         [0055]    (5) The method for fabricating a III-nitride semiconductor light-emitting device including a scattering surface formed by an etching and epitaxial growth. 
         [0056]    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. 
         [0057]    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.