Patent Publication Number: US-2011073894-A1

Title: Light-emitting diode and method for manufacturing the same

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     Some references, which may include patents, patent applications and various publications, are cited and discussed in the description of this invention. The citation and/or discussion of such references is provided merely to clarify the description of the present invention and is not an admission that any such reference is “prior art” to the invention described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference were individually incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates generally to a light emitting diode (LED), and more particular to an LED that utilizes a structure of flat surface regions formed under n-type and p-type electrodes and rough surface regions formed outside the n-type and p-type electrodes to enhance the wiring boding stability and improve the light extraction efficiency of the LED. 
     BACKGROUND OF THE INVENTION 
     Light emitting diodes (LEDs) have been widespread used for lighting with great brightness. Typically, an LED includes a multilayered structure having a p-type semiconductor, an n-type semiconductor and an active layer sandwiched between the p-type and n-type semiconductors, p-type and n-type electrodes placed on the surfaces of the multilayered structure. In operation, a current is injected into the LED from the p-type and n-electrodes, which spreads into the respective semiconductor layers. Light is generated when the current flows across the active layer because of the recombination of minority carriers at the active layer. Generally, the generated light from the active layer may be reflected to different degrees, thereby degrading the light extraction efficiency. In order to improve the light extraction efficiency, a rough surface is usually formed on the p-type semiconductor, by adjusting epitaxial parameters during the epitaxial growth of the p-type semiconductor layer. 
       FIG. 6  shows a conventional LED  200 . The LED  200  includes a substrate  202  and a n-type semiconductor layer  204 , a light emitting layer  206 , a p-type semiconductor layer  208 , a transparent conductive layer  212  sequentially stacked on the substrate  202 , and a p-type electrode  216  disposed on the transparent conductive layer  212  and an n-type electrode  220  disposed on an exposed portion of the n-type semiconductor layer  204 . To improve the light extraction efficiency, a rough surface  210  is formed on the p-type semiconductor  208 , by adjusting epitaxial parameters during the epitaxial growth of the p-type semiconductor layer. As such, the transparent conductive layer  212  also has a rough surface  214 . Additionally, after a light emitting area is defined, the exposed portion of the n-type semiconductor layer  204  also has a rough surface  222  similar to the rough surface  210  of the p-type semiconductor layer  208 . As a result, the rough surface profile  210  of the p-type semiconductor layer  208  and the rough surface profile  222  of the exposed portion of the n-type semiconductor layer  204  result in a rough surface  224  in the p-type electrode  216  and a rough surface  226  in the n-type electrode  204 , respectively. 
     As shown in  FIG. 6 , because the rough surface  210  of the p-type semiconductor layer  208  may result in poor step coverage of the transparent conductive layer  212  during the deposition of the transparent conductive layer  212 , the current flow in the transparent conductive layer  212  may be discontinued at some points. This will reduce the current spreading ability of the transparent conductive layer  212  and thus give rise to increase of the operation voltage Vf and non-uniformity of the current density, thereby, affecting the lifetime and the operation stability of the LED. Further, for the deposition of the transparent conductive layer  212  having the rough surface  214  with large depth-to-width ratios of dents, voids  218  may be formed in the transparent conductive layer  212 . The presence of the voids  218 , which may contain air, chemical remains and/or photoresists, degrades the reliability of the LED. In addition, because of the rough surface profile  224  of the p-type electrode  216 , dusts such as wax and chemical remains produced on the rough surface  224  during the manufacture process may not easily be cleaned, which reduces the adhesion of the wire bonding in the packaging, and thus, degrades the reliability and the yield rate of the wire bonding, which in turn, reduce the reliability and the stability of the LED. 
     Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies. 
     SUMMARY OF THE INVENTION 
     Accordingly, the objectives of the present invention are to provide novel structures of an LED which overcome the aforementioned problems described above. 
     One objective of the present invention is to provide an LED having flat surface regions on which a p-type electrode and an n-type electrode are disposed and rough surface regions for improving the stability of the wiring bonding and the light extraction efficiency. 
     Another objective of the present invention is to provide an LED having a p-type semiconductor layer with at least flat surface region in which p+ doped semiconductors are removed and a transparent conductive layer such that in operation, a current flow vertically from the transparent conductive layer to the at least flat surface region of the p-type semiconductor layer is blocked, thereby, avoiding the current congestion effect under the flat surface region, and increasing the light emitting efficiency of the LED. 
     Yet another objective of the present invention is to provide an LED having a p-type semiconductor layer with at least flat surface region, a transparent conductive layer and a reflective layer formed between the at least flat surface region of the p-type semiconductor layer and the transparent conductive layer such that in operation, a current flow vertically from the at least flat surface region of the p-type semiconductor layer to the transparent conductive layer is blocked, thereby, avoiding the current congestion effect under the flat surface region, and increasing the light emitting efficient of the LED. 
     A further another objective of the present invention is to provide methods of manufacturing the above LEDs. 
     In one aspect, the present invention relates to an LED. In one embodiment, the LED includes a substrate; a first semiconductor layer disposed on the substrate, having a first portion and a second portion extending from each other, wherein the first portion has a rough surface region and a flat surface region recessed relative to the rough surface region; a light emitting layer disposed on the second portion of the first semiconductor layer, defining a light emitting region thereon; a second semiconductor layer disposed on the light emitting layer, having a rough surface region and at least one flat surface region recessed relative to the rough surface region, wherein the first semiconductor layer and the second semiconductor layer have different electrical conductivities; an insulative layer disposed on the at least flat surface region of the second semiconductor layer; a transparent conductive layer disposed on the insulative layer and the rough surface region of the second semiconductor layer such that the transparent conductive layer has a rough surface region and a flat surface region corresponding to the rough surface region and the at least one flat surface region of the second semiconductor layer, respectively; a first electrode disposed on the flat surface region of the first semiconductor layer; and a second electrode disposed on the flat surface region of the transparent conductive layer. 
     The LED further includes a passivation layer disposed on the rough surface region of the transparent conductive layer and the rough surface region of the first portion of the first semiconductor. 
     In one embodiment, the first semiconductor layer is formed of an n-type semiconductor, and the second semiconductor layer is formed of a p-type semiconductor. The first electrode is an n-type electrode, and the second electrode is a p-type electrode. 
     In one embodiment, the insulative layer has a thickness greater than about 5 nm. In another embodiment, the insulative layer has an area greater than the at least one flat surface region of the second semiconductor layer. In yet another embodiment, the insulative layer comprises a multilayer having a reflective characteristic greater than about 50%. The insulative layer is formed of SiO 2 , SiN, TiO 2  or Al 2 O 3 . 
     In another aspect of the present invention, an LED includes a substrate; a first semiconductor layer disposed on the substrate; a light emitting layer disposed on the first semiconductor layer; a second semiconductor layer disposed on the light emitting layer, having a rough surface region and at least one flat surface region, wherein the first semiconductor layer and the second semiconductor layer have different electrical conductivities; a transparent conductive layer disposed on the second semiconductor layer such that the transparent conductive layer has a rough surface region and a flat surface region corresponding to the rough surface region and the at least one flat surface region of the second semiconductor layer, respectively; a first electrode electrically coupled to the first semiconductor layer; and a second electrode disposed on the flat surface region of the transparent conductive layer. In operation, no current flows vertically from the flat surface region of the transparent conductive layer to the at least one flat surface region of the second semiconductor layer. 
     In one embodiment, the at least one flat surface region of the second semiconductor layer is recessed relative to the rough surface region of the second semiconductor layer. 
     In one embodiment, the first semiconductor layer has a first portion and a second portion extending from each other, where the first portion has a rough surface region and a flat surface region. The first electrode disposed on the flat surface region of the first portion of the first semiconductor layer. The light emitting layer disposed on the second portion of the first semiconductor layer so as to define a light emitting region thereon. 
     In one embodiment, the flat surface region of the first semiconductor layer is recessed relative to the rough surface region of the first semiconductor layer. 
     The first semiconductor layer is formed of an n-type semiconductor, and the second semiconductor layer is formed of a p-type semiconductor, and wherein the first electrode is an n-type electrode, and the second electrode is a p-type electrode. 
     In one embodiment, the second semiconductor layer comprises a p-type semiconductor layer formed on the light emitting layer; and a p+ doped semiconductor layer formed on the rough surface region of the p-type semiconductor layer. 
     In one embodiment, the flat surface region of the transparent conductive layer and the at least one flat surface region of the second semiconductor layer are in a Schottky contact. 
     The LED further includes a reflective layer formed between the flat surface region of the transparent conductive layer and the at least one flat surface region of the second semiconductor layer. In one embodiment, the reflective layer has an area greater than the at least one flat surface region of the second semiconductor layer. In another embodiment, the reflective layer comprises an insulative layer, a stacked structure of an insulative layer and a metal layer, or a metal layer. In another embodiment, the reflective layer comprises a single layer, or a multilayer. 
     Additionally, the LED also includes a passivation layer disposed on the rough surface region of the transparent conductive layer and the rough surface region of the first portion of the first semiconductor. 
     In yet another aspect of the present invention, a method of manufacturing an LED, comprising the steps of providing a substrate; and sequentially forming an n-type semiconductor layer on the substrate, a light emitting layer on the n-type semiconductor layer, and a p-type semiconductor layer on the light emitting layer, wherein the p-type semiconductor layer has a rough surface having a first region, a second region and a third region separated from the second region. 
     In one embodiment, the p-type semiconductor layer comprises a p-type semiconductor layer formed on the light emitting layer; and a p+ doped semiconductor layer formed on the p-type semiconductor layer. In one embodiment, the p-type semiconductor layer has at least a fourth region extending from the second region, wherein the fourth region is adapted for forming a fourth flat surface region. 
     Each of the n-type semiconductor layer, the light emitting layer and the p-type semiconductor layer is formed of a GaN based material. 
     Furthermore, the method includes the steps of forming a first mask layer on the first region of the rough surface of the p-type semiconductor layer, thereby exposing the second and third regions of the rough surface of the p-type semiconductor layer; and forming a second mask layer on the first mask layer and the exposed second and third regions of the rough surface of the p-type semiconductor layer, wherein the second mask layer and the p-type semiconductor layer have a substantially same etching rate, wherein the first mask layer has an etching rate less than that of the second mask layer and the p-type semiconductor layer; 
     In one embodiment, the first mask layer is formed of SiO 2 , SiNx, SiO x N y , BPSG, spin-on-glass (SOG), or polyimide. In one embodiment, the second mask layer is formed of a photoresist (PR) material. In another embodiment, the second mask layer is formed of a SOG material. 
     Moreover, the method includes the steps of performing an etching process on the second mask layer and the first mask layer so as to form a first flat surface region and a second flat surface region in the second and third regions of the p-type semiconductor layer, respectively, and to expose the rough surface of the first region of the p-type semiconductor layer; and removing a portion of the p-type semiconductor layer in which the second flat surface region is located and a corresponding portion of the light emitting layer so as to expose a portion of the n-type semiconductor layer, and forming a third flat surface region on the exposed portion of the n-type semiconductor layer. In one embodiment, the third flat surface region on the exposed portion of the n-type semiconductor layer is corresponding to the second flat surface region of the p-type semiconductor layer, and wherein the exposed portion of the n-type semiconductor layer further has a rough surface region extending from the third flat surface region. 
     In one embodiment, the etching process is performed with a dry etching process, where the dry etching process comprises an inductively coupled plasma (ICP) process, or a reactive ion etch (RIE) process. In one embodiment, the etching process further comprises removing the p+ doped semiconductor layer in the second and third regions of the p-type semiconductor layer. 
     Additionally, the method also includes the steps of forming a transparent conductive layer on the rough surface region and the first flat surface region of the p-type semiconductor layer, such that the transparent conductive layer has a rough surface region and a flat surface region corresponding to the rough surface region and the first flat surface region of the p-type semiconductor layer, respectively; and forming an n-type electrode on the third flat surface region of the n-type semiconductor layer and a p-type electrode on the flat surface region of transparent conductive layer. 
     In one embodiment, the flat surface region of transparent conductive layer and the first flat surface region of the second semiconductor layer are in a Schottky contact. 
     In one embodiment, the method also includes the step of forming a reflective layer between the flat surface region of the transparent conduct layer and the first flat surface region of the p-type semiconductor layer. 
     The method may also includes the step of forming a passivation layer on the rough surface region of the exposed portion of the n-type semiconductor layer and the rough surface region of the transparent conductive layer, after forming the n-type electrode and the p-type electrode. 
     These and other aspects of the present invention will become apparent from the following description of the preferred embodiment taken in conjunction with the following drawings, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate one or more embodiments of the invention and together with the written description, serve to explain the principles of the invention. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment, and wherein: 
         FIGS. 1A-1E  show schematically a cross-sectional view of an LED and its manufacturing process according to one embodiment of the present invention; 
         FIGS. 2A-2D  show schematically a cross-sectional view of an LED and its manufacturing process according to another embodiment of the present invention; 
         FIG. 3  shows schematically a cross-sectional view of an LED according to yet another embodiment of the present invention; 
         FIGS. 4A and 4B  show schematically a top view and a cross-sectional view, respectfully, of an LED according to an alternative embodiment of the present invention; 
         FIG. 5  shows schematically a cross-sectional view of an LED according to a further embodiment of the present invention; and 
         FIG. 6  shows schematically a cross-sectional view of a conventional LED. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout. 
     Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “covering” another element or layer, it may be directly on, connected to, coupled to, or covering the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” or “has” and/or “having” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element&#39;s relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower”, can therefore, encompasses both an orientation of “lower” and “upper,” depending of the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     The term “layer”, as used herein, refers to a thin sheet or thin film. 
     The term “electrode”, as used herein, is an electrically conductive layer or film formed of one or more electrically conductive materials. 
     The description will be made as to the embodiments of the present invention in conjunction with the accompanying drawings of  FIGS. 1-5 . In accordance with the purposes of this invention, as embodied and broadly described herein, this invention, in one aspect, relates to an LED and method of manufacturing same. 
     Referring to  FIGS. 1A-1E , an LED  100 A and its manufacturing process are schematically shown according to one embodiment of the present invention. As shown in  FIG. 1E , the LED  100 A includes a substrate  101 , a first semiconductor layer  102  disposed on the substrate  101 . The first semiconductor layer  102  has a first portion  138  and a second portion  140  extending from each other, where the first portion  138  has a rough surface region  142  and a flat surface region  130  recessed relative to the rough surface region  142 . 
     The LED  100 A further includes a light emitting layer  104  disposed on the second portion  140  of the first semiconductor layer  102 , defining a light emitting region  141  thereon, and a second semiconductor layer  110  disposed on the light emitting layer  104 . The second semiconductor layer  110  has a rough surface region  112  and a flat surface region  126 . The flat surface region  126  is recessed relative to the rough surface region  112  to define a depth, H 2 , and has a dimension, D 1 , for example, a diameter. The depth H 2  of the flat surface region  126  is less than a thickness, H 1 , of the second semiconductor layer  106 , as shown in  FIG. 1D . In one embodiment, additional flat surface regions may be defined in the second semiconductor layer  106 . 
     The first semiconductor layer  102  and the second semiconductor layer  110  have different electrical conductivities. For example, the first semiconductor layer  102  comprises an n-type semiconductor, while the second semiconductor layer  110  comprises a p-type semiconductor  106 . Further, the second semiconductor layer  110  has a p+ doped semiconductor layer  108  is formed on the rough surface region  112  of the p-type semiconductor layer  106 , so that the p+ doped semiconductor layer  108  also has a rough surface  114  as well. 
     Additionally, the LED  100 A also includes an insulative layer  160  disposed on the flat surface region  126  of the second semiconductor layer  106 . The insulative layer  160  is adapted for blocking an injected current flow vertically from the p-type electrode  134  to the flat surface region  126  of the second semiconductor layer  110 . In this exemplary embodiment, the insulative layer  160  has an area greater than the flat surface region  126  of the second semiconductor layer  106 . As shown in  FIG. 1D , for example, the insulative layer  160  is characterized with a dimension or diameter, D 2 , which is larger than the dimension D 1  of the flat surface region  126  of the second semiconductor layer  106 . In one embodiment, the insulative layer  160  has a thickness greater than about 5 nm. The insulative layer  160  may be formed of SiO 2 , SiN, TiO 2 , Al 2 O 3 , or the likes. In one embodiment, the insulative layer  160  is formed in a multilayer having a reflective characteristic greater than about 50%. 
     Furthermore, the LED  100 A includes a transparent conductive layer  132  disposed on the insulative layer  160  and the rough surface region  112  of the second semiconductor layer  110 . According to the present invention, the transparent conductive layer  132  also has a rough surface region  151  and a flat surface region  150  that are corresponding to the rough surface region  112  and the flat surface region  126  of the second semiconductor layer  110 , respectively. 
     The LED  100 A has an n-type electrode  136  formed on the flat surface region  130  of the first semiconductor layer  102 , and a p-type electrode  134  formed on the flat surface region  150  of the transparent conductive layer  132 . 
     The LED  100 A may also include a passivation layer (not shown), selectively disposed on the rough surface region  151  of the transparent conductive layer  132  and the rough surface region  142  of the first portion  138  of the first semiconductor  102 . 
     In one embodiment, the LED  100 A can be manufactured according to the processes shown in  FIGS. 1A-1D . First, the substrate  101  is provided. An epitaxial growth process is then applied on the substrate  101  to sequentially form the n-type semiconductor layer  102  on the substrate  101 , the light emitting layer  104  on the n-type semiconductor layer  102 , and the p-type semiconductor layer  106  on the light emitting layer  104  and the p+ doped semiconductor layer  108  on the p-type semiconductor layer  106 . By adjusting epitaxial parameters during the epitaxial growth of the p-type semiconductor layer  106 , a rough surface  112  can be formed thereon. Accordingly, the p+ doped semiconductor layer  108  also has a rough surface  114 . The rough surface  112  can improve the efficiency of the light extraction of the LED  100 A. The rough surface  112  defines a first region  116 , a second region  118  and a third region  120  separated from the second region  118 . The n-type semiconductor layer, the light emitting layer and the p-type semiconductor layer can be formed of GaN based materials, or the likes. 
     After the growth of the epitaxial structure, a first mask layer  122  is formed on the rough surface  112  of the p-type semiconductor layer  106 , for example, by a chemical vapor deposition (CVD), a physical vapor deposition (PVD) or a spin-on coating process. Then, a pattern definition process such as photolithography and/or etching is applied to the first mask layer  122  to remove portions of the first mask layer  122  from the second region  118  and a third region  120  of the rough surface  112  of the p-type semiconductor layer  106 , so as to expose the second region  118  and a third region  120  of the rough surface  112  of the p-type semiconductor layer  106 , as shown in  FIG. 1A . Next, a second mask layer  124  is formed on the first mask layer  122  and the exposed second and third regions  118  and  120  of the rough surface  112  of the p-type semiconductor layer  106 , as shown in  FIG. 1B . 
     According to the present invention, the second mask layer  124  and the p-type semiconductor layer  106  have a substantially same etching rate, while the first mask layer  122  has an etching rate less than that of the second mask layer  124  and the p-type semiconductor layer  106 . The first mask layer  122  can be formed of SiO 2 , SiNx, SiO x N y , BPSG, SOG, polyimide, or the likes. The first mask layer  122  has a thickness in a range of about 10-1000 nm. The second mask layer  124  is formed of a material of high viscosity such as a photoresist (PR) material, or an SOG material. 
     The next step is to form the flat surface regions  126  and  128  in the p-type semiconductor layer  106 , by, for example, an etching process. Since the materials of the second mask layer  124  and the p-type semiconductor layer  106  are selected to have etching rates that are same or substantially similar, and the material of the first mask layer  122  has an etching rate less than that of the second mask layer  124  and the p-type semiconductor layer  106 , the etching process results in the formation of the first and second flat surface regions  126  and  128  in the second and third regions  118  and  120  of the p-type semiconductor layer  106 , respectively, as shown in  FIG. 2C . In one embodiment, the etching process is performed with a dry etching process. The dry etching process can be an inductively coupled plasma (ICP) process, or a reactive ion etch (RIE) process. After the etching process, the first and second mask layers  122  and  124  are removed, thereby, exposing the rough surface region  112  of the first region  116  of the p-type semiconductor layer  106 , as shown in  FIG. 1D . 
     The insulative layer  160  is then formed on the first flat surface region  126  of the second semiconductor layer  106 , as shown in  FIG. 1D . 
     Consequently, the pattern definition process such as photolithography and/or etching is applied to remove a portion of the second semiconductor layer  110 , for example, the portion in which the second flat surface region  128  is located, and a corresponding portion of the light emitting layer  104  so as to expose the first portion  138  of the n-type semiconductor layer  102 . The remaining light emitting layer  104  and the remaining p-type semiconductor layer  106  are located over the second portion  140  of the n-type semiconductor layer  102 , which constitute the light emitting area  141 . After the light emitting area  141  is defined, the surface profile of the rough surface region  112  of the p-type semiconductor layer  106  is transferred to the exposed portion  138  of the n-type semiconductor layer  102 . Therefore, the exposed portion  138  of the n-type semiconductor layer  102  has a flat surface region  130  and a rough surface region  142 , which are corresponding to the second flat surface region  128  of the second semiconductor layer  110  and the rough surface region  112  of the p-type semiconductor layer  106 , respectively. In this embodiment, the flat surface region  130  is recessed relative to the rough surface region  142  of the n-type semiconductor layer  102 . 
     Then, the transparent conductive layer  132  is formed on the rough surface region  112  and the first flat surface region  126  of the p-type semiconductor layer  106 , by a vapor deposition method such as CVD, or PVD. The transparent conductive layer  132  has a rough surface region  151  and a flat surface region  150  corresponding to the rough surface region  112  and the first flat surface region  126  of the p-type semiconductor layer  106 , respectively. The transparent conductive layer  132  is formed of a transparent conductive material, for example, ITO. 
     The n-type electrode  136  and the p-type electrode  134  are formed on the flat surface region  130  of the n-type semiconductor layer  102  and the flat surface region  150  of transparent conductive layer  132 , respectively, for example, by a vapor deposition method such as CVD, or PVD. 
     Referring to  FIGS. 2A-2D , an LED  100 B and its manufacturing process are schematically shown according to another embodiment of the present invention. The LED  100 B is structurally similar to the LED  100 A shown in  FIG. 1E , except that the LED  100 B do not have an insulative layer  160 . As shown in  FIG. 2D , the LED  100 B includes a substrate  101 , a first semiconductor layer  102 , a light emitting layer  104 , a second semiconductor layer  110 , a transparent conductive layer  132  and a passivation layer  152  sequentially stacked together. The first semiconductor layer  102  and the second semiconductor layer  110  have different electrical conductivities. For example, the first semiconductor layer  102  comprises an n-type semiconductor, while the second semiconductor layer  110  comprises a p-type semiconductor. 
     Specifically, the first semiconductor layer  102  is disposed on the substrate  101 , having a first portion  138  and a second portion  140  extending from each other. The first portion  138  has a rough surface region  142  and a flat surface region  130  recessed relative to the rough surface region  142 . 
     The light emitting layer  104  is disposed on the second portion  140  of the first semiconductor layer  102 , defining a light emitting region thereon  141 , which is over the second portion  140  of the first semiconductor layer  102 . 
     The second semiconductor layer  110  has a p-type semiconductor layer  106  disposed on the light emitting layer  104 . The p-type semiconductor layer  106  has a rough surface region  112  and a flat surface region  126  recessed relative to the rough surface region  112 . Further, the second semiconductor layer  110  has a p+ doped semiconductor layer  108  is formed on the rough surface region  112  of the p-type semiconductor layer  106 , so that the p+ doped semiconductor layer  108  also has a rough surface  114  as well. 
     The transparent conductive layer  132  is disposed on the rough surface region  114  of the p+ doped semiconductor layer  108  and the flat surface region  126  of the p-type semiconductor layer  106  such that the transparent conductive layer  132  has a rough surface region  151  and a flat surface region  126  corresponding to the rough surface region  114  and the flat surface region  126  of the second semiconductor layer  110 , respectively. 
     Further, an n-type electrode  136  is disposed on the flat surface region  130  of the first semiconductor layer  102 , and a p-type electrode is disposed on the flat surface region  150  of the transparent conductive layer  132 . 
     The passivation layer  152  is disposed on the rough surface region  151  of the transparent conductive layer  132 . 
     As shown in  FIG. 2A , to manufacture such an LED  100 B, the substrate  101  is provided. Then, an epitaxial growth process is applied on the surface  148  of the substrate  101  to sequentially form the n-type semiconductor layer  102  on the substrate  101 , the light emitting layer  104  on the n-type semiconductor layer  102 , and the p-type semiconductor layer  106  on the light emitting layer  104 , and the p+ doped semiconductor layer  108  on the p-type semiconductor layer  106 . In this exemplary embodiment, the second semiconductor layer  110  has two layers of the p-type semiconductor layer  106  and the p+ doped semiconductor layer  108 . The n-type semiconductor layer, the light emitting layer and the p-type semiconductor layer can be formed of GaN based materials, or the likes. 
     In order to improve the efficiency of the light extraction, the p-type semiconductor layer  106  is formed to have a rough surface  112 . This can be implemented, for example, adjusting epitaxial parameters during the epitaxial growth of the p-type semiconductor layer  106 . Accordingly, the p+ doped semiconductor layer  108  also has a rough surface  114 . The rough surface  112  and thus the rough surface  114  defines a first region  116 , a second region  118  and a third region  120  separated from the second region  118 . 
     Further, a first mask layer  122  is formed on the rough surface  114  of the second semiconductor layer  110 , for example, by a CVD, a PVD or a spin-on coating process. Then, pattern definition processes such as photolithography and etching are applied to the first mask layer  122  to remove portions of the first mask layer  122  from the second region  118  and a third region  120  of the rough surface  114  of the second semiconductor layer  110 , so as to expose the second region  118  and a third region  120  of the rough surface  114  of the second semiconductor layer  110 . The first mask layer can be formed of SiO 2 , SiNx, SiO x N y , BPSG, SOG, polyimide, or the likes. 
     As shown in  FIG. 2B , the next step is using a spin coating process to form a second mask layer  124  on the first mask layer  122  and the exposed second and third regions  118  and  120  of the rough surface  114  of the second semiconductor layer  110 . As a result, the surfaces of the second mask layer  124  over the second and third regions  118  and  120  are flat. 
     According to the present invention, the second mask layer  124  and the second semiconductor layer  110  have a substantially same etching rate, while the first mask layer  122  has an etching rate less than that of the second mask layer  124  and the second semiconductor layer  110 . In one embodiment, the second mask layer  124  is formed of a material of high viscosity such as a PR material, or an SOG material. 
     Afterwards, an etching process is performed on the second mask layer  124  and the second and third regions  118  and  120  of the second semiconductor layer  110 . Since the materials of the second mask layer  124  and the second semiconductor layer  110  are selected to have etching rates that are same or substantially similar, and the material of the first mask layer  122  has an etching rate less than that of the second mask layer  124  and the second semiconductor layer  110 , and further, the surfaces of the second mask layer  124  over the second and third regions  118  and  120  are flat, in the etching process the etching rates of the second mask layer  124  and the second semiconductor layer  110  are same or substantially close, therefore, the flat profiles of the second mask layer  124  over the second and third regions  118  and  120  can be transferred to the second semiconductor layer  110 , so that the first and second flat surface regions  126  and  128  are formed in the second and third regions  118  and  120  of the second semiconductor layer  110 , respectively, as shown in  FIG. 2C . The flat surface region  126  is adapted for the p-type electrode  134 , and thus called an electrode region. In one embodiment, the etching process is performed with a dry etching process. The dry etching process can be an ICP process, or an RIE process. 
     In one embodiment, the etching process also includes removing the p+ doped semiconductor layer  108  from the second and third regions  118  and  120  of the second semiconductor layer  110 , which are adapted for current blocking. Accordingly, the p+doped semiconductor layer  108  exists only in the first region  116  of the second semiconductor layer  110 . After the etching process, the first and second mask layers  122  and  124  are removed, thereby, exposing the rough surface region  114  of the first region  116  of the second semiconductor layer  110 . 
     Next steps include defining the light emitting area  141  and forming the transparent conductive layer  132 , as shown in  FIG. 2D . The order of performing the two steps is in accordance with the need of the manufacture process. In one embodiment, the light emitting area  141  is defined first, which uses the pattern definition process such as photolithography and/or etching are applied to remove a portion of the second semiconductor layer  110 , for example, the portion in which the second flat surface region  128  is located, and a corresponding portion of the light emitting layer  104  so as to expose the first portion  138  of the n-type semiconductor layer  102 . The remaining light emitting layer  104  and the remaining second semiconductor layer  110  are located over the second portion  140  of the n-type semiconductor layer  102 , constituting the light emitting area  141 . After defining the light emitting area  141 , the surface profile of the rough surface region  114  of the second semiconductor layer  110  is transferred to the exposed portion  138  of the first semiconductor layer  102 . Therefore, the exposed portion  138  of the first semiconductor layer  102  has a flat surface region  130  and a rough surface region  142 , which are corresponding to the second flat surface region  128  of the second semiconductor layer  110  and the rough surface region  114  of the second semiconductor layer  110 , respectively. The flat surface region  130  is adapted for the n-type electrode  136 , and thus called an electrode region. In this embodiment, the flat surface region  130  is recessed relative to the rough surface region  142  of the first semiconductor layer  102 . Similarly, the flat surface region  126  is recessed relative to the rough surface region  114  of the second semiconductor layer  110 . 
     Then, the transparent conductive layer  132  is formed on the rough surface region  114  and the first flat surface region  126  of the second semiconductor layer  110 , by a vapor deposition method such as CVD, or PVD. The transparent conductive layer  132  has a rough surface region  151  and a flat surface region  150  corresponding to the rough surface region  114  and the first flat surface region  126  of the second semiconductor layer  110 , respectively. The transparent conductive layer  132  is formed of a transparent conductive material, for example, ITO. 
     The n-type electrode  136  and the p-type electrode  134  are formed on the flat surface region  130  of the n-type semiconductor layer  102  and the flat surface region  150  of transparent conductive layer  132 , respectively, for example, by a vapor deposition method such as CVD, or PVD. 
     The passivation layer  152  is then selectively formed on the rough surface region  151  of the transparent conductive layer  132 , and optionally on the rough surface region  142  of the exposed portion  138  of the n-type semiconductor layer  102 . 
     According to the processes as set forth above, the p+ doped semiconductor  108  under the p-type electrode  134  is removed. Therefore, the flat surface region  150  of transparent conductive layer  132  and the first flat surface region  126  of the second semiconductor layer  110  are in a Schottky contact having a Schottky barrier which blocks a current injected from the p-type electrode  134  flowing from the transparent conductive layer  132  under the p-type electrode  134  to the first flat surface region  126  of the second semiconductor layer  110 , thereby, forcing the injected current spreading laterally along the flat surface region  150  of transparent conductive layer  132 , improving the current distribution and the efficiency of the light emitting of the LED  100 B. 
     Referring to  FIG. 3 , a further embodiment of an LED  100 C is schematically shown according to the present invention. The LED  100 C is structurally similar to the LED  100 B of  FIG. 2D , except that the LED  100 C includes a reflective layer  146  formed between the transparent conduct layer  132  and the first flat surface region  126  of the second semiconductor layer  110 . The reflective layer  146  is formed after the light emitting area  141  is defined, but before the transparent conductive layer  132  is formed. 
     The reflective layer  146  can be formed in a single layer, or a multilayer. The reflective layer  146  includes an insulative layer, a stacked structure of an insulative layer and a metal layer, or a metal layer. The metal layer is formed of high reflective metal material such as, but not limited to, aluminum, silver, platinum, etc. The insulative layer is formed of, but not limited to, SiO 2 , SiN, TiO 2  or Al 2 O 3 , etc. Additionally, the reflective layer  146  can be a distributed Bragg reflector (DBR) formed in a stack of multiple insulative layers. 
     Referring to  FIGS. 4A and 4B , an LED  100 D is schematically shown according to yet a further embodiment of the present invention. The LED  100 D is structurally similar to the LED  100 B of  FIG. 2D , except that in the LED  100 D, the surface  114  of the second semiconductor layer  110  includes additional flat surface regions  154  and  156  extending from the p-type electrode  134 , as shown in  FIG. 4A . 
     The manufacturing processes of the LED  100 D is similar to that of LED  100 B as shown in  FIGS. 2A-2D , except that when forming the first mask layer  122 , additional desired regions of the surface  114  of the second semiconductor layer  110  are also exposed. Following the processes described above, these additional desired regions are formed into additional flat surface regions, such as flat surface regions  154  and  156  of the second semiconductor layer  110 , as shown in  FIG. 4B . The thickness of the transparent conductive layer  132  is uniform over the flat surface regions  154  and  156  of the second semiconductor layer  110 . Comparing to the rough surface region  151 , the transparent conductive layer  132  over the additional flat surface regions  154  and  156  has relative low resistance, and is used for paths of uniform current spreading. This enhances the current spreading ability of the LED  100 D, thereby, increasing the light emitting efficiency of the LED  100 D. 
     In one embodiment, the p-type electrode  134  may be selectively extended to the transparent conductive layer  132  over the additional flat surface regions  154  and  156  of the second semiconductor layer  110 , so as to further increase the uniformity of the current distribution. Furthermore, the reflective layer  146  and/or the insulative layer  160  may be selectively formed between the transparent conductive layer  132  and the additional flat surface regions  154  and  156  of the second semiconductor layer  110 , as shown in  FIG. 5  of an LED  100 E according to one embodiment of the present invention. 
     The present invention recites an LED and method of manufacturing same, which, among other things, has a great deal of advantages. For example, the structures of the flat surface regions formed under the n-type and p-type electrodes and the rough surface regions formed outside the n-type and p-type electrodes not only enhance the wiring boding stability but improve the light extraction efficiency of the LED. 
     Additionally, the n-type and p-type electrodes disposed on the flat surface regions also have flat surfaces, which could reduce the color shading of the n-type and p-type electrodes, and improve the accuracy of the electrode identification of packaging equipments, thereby, improving the accuracy of wire bonding positions. 
     Further, according to the present invention, the LED has a p-type semiconductor layer with the flat surface regions in which p+ doped semiconductors are removed, which provides a barrier, such as a Schottky barrier, for current blocking. Yet, an insulative layer formed between the flat surface regions of the p-type semiconductor layer and the transparent conductive layer also provides the current blocking effect. Accordingly, in operation, a current flow vertically from the p-type electrode to the flat surface regions of the p-type semiconductor layer is blocked, thereby, avoiding the current congestion effect under the flat surface regions, and increasing the light emitting efficiency of the LED. 
     Another advantage of the present invention is during the manufacture of the LED, desired portions of the light emitting area can selectively be flattened, such that the thickness of the transparent conductive layer over the flattened area/region is uniform. Comparing to the rough surface region, the transparent conductive layer over the additional flat surface regions has relative low resistance, and is used for paths of uniform current spreading. This enhances the current spreading ability of the LED  100 D, thereby, further increasing the light emitting efficiency of the LED. 
     Although the embodiments of the present invention are described for horizontal type LEDs, one skilled in the art should appreciate that the present invention can also be applied to vertical type LEDs. For example, if the etching process is applied to only the region  118  to form a flat surface region thereon, and no flattening (e.g., etching) process is performed on the first semiconductor layer  102 , a vertical type LED will be fabricated according to the processes of the present invention. 
     The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. 
     The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to activate others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.