Abstract:
A vertical GaN-based LED and a method of manufacturing the same are provided. The vertical GaN-based LED can prevent the damage of an n-type GaN layer contacting an n-type electrode, thereby stably securing the contact resistance of the n-electrode. The vertical GaN-based LED includes: a support layer; a p-electrode formed on the support layer; a p-type GaN layer formed on the p-electrode; an active layer formed on the p-type GaN layer; an n-type GaN layer for an n-type electrode contact, formed on the active layer; an etch stop layer formed on the n-type GaN layer to expose a portion of the n-type GaN layer; and an n-electrode formed on the n-type GaN layer exposed by the etch stop layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 2005-117958 filed with the Korean Industrial Property Office on Dec. 6, 2005, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vertical gallium-nitride (GaN)-based light emitting diode (LED), and more particularly, to a vertical GaN-based LED that can prevent the damage of an n-type GaN layer contacting an n-electrode. Thus, the vertical GaN-based LED can stably secure the contact resistance of the n-electrode, reduce the operating voltage, and improve the luminous efficiency. 
     2. Description of the Related Art 
     Generally, GaN-based LEDs are grown on a sapphire substrate. The sapphire substrate is rigid and electrically nonconductive and has a low thermal conductivity. Therefore, it is difficult to reduce the size of the GaN-based LED for cost-down or improve the optical power and chip characteristics. Particularly, heat dissipation is very important for the LEDs because a high current should be applied to the GaN-based LEDs so as to increase the optical power of the GaN-based LEDs. 
     To solve these problems, a vertical GaN-based LED has been proposed. In the vertical GaN-based LED, the sapphire substrate is removed using a laser lift-off (hereinafter, referred to as LLO) technology. 
     A method of manufacturing a vertical GaN-based LED according to the related art will be described below with reference to  FIGS. 1A to 1D . 
       FIGS. 1A to 1D  are sectional views illustrating a method of manufacturing a vertical GaN-based LED according to the related art. 
     Referring to  FIG. 1A , an undoped GaN layer  101  and a lightly doped n-type GaN layer  102  are sequentially grown on a sapphire substrate  100 . A heavily doped n-type GaN layer (that is, an n-type GaN layer  103  for an n-type electrode contact), a GaN/InGaN active layer  104  with a multi-quantum well structure, and a p-type GaN layer  105  are sequentially grown on the lightly doped n-type GaN layer  102 . Then, a p-electrode  106  is formed on the p-type GaN layer  105 . 
     A plating seed layer (not shown) is formed on the p-electrode  106 . A support layer  107  is formed on the plating seed layer by electrolyte plating or electroless plating. The plating seed layer serves as a plating crystal nucleus when the plating process is performed for forming the support layer  107 . The support layer  107  supports the final LED structure and serves as an electrode. 
     Referring to  FIG. 1B , the sapphire substrate  100  is removed using an LLO process. 
     Referring to  FIG. 1C , the undoped GaN layer  101  and the lightly doped n-type GaN layer  102  exposed by the process of removing the sapphire substrate  100  are removed to expose the n-type GaN layer  103  for the n-type electrode contact. By removing the undoped GaN layer  101  and the lightly doped n-type GaN layer  102 , the n-type GaN layer  103  (that is, the heavily doped n-type GaN layer) contacts an n-electrode  110 , which will be formed later. Therefore, the contact resistance of the n-electrode  110  is reduced and the operating voltage is reduced. The removing process may be achieved by a general etching process. 
     Referring to  FIG. 1D , an n-electrode  110  is formed on the exposed n-type GaN layer  103 . Prior to the formation of the n-electrode  110  on the n-type GaN layer  103 , an n-type transparent electrode  108  for improving the current spreading effect and an n-type reflective electrode  109  for improving the light efficiency may be sequentially formed on the n-type GaN layer  103 . 
     However, the method of manufacturing the vertical GaN-based LED according to the related art has the following problems.  FIG. 2  is a sectional view for explaining the problems of the related art. 
     When etching the undoped GaN layer  101  and the lightly doped n-type GaN layer  102  exposed by the removal of the sapphire substrate  100 , there is almost no difference of the etching selectivity in the lightly doped n-type GaN layer  102  and the n-type GaN layer  103  and thus the surface of the n-type GaN layer  103  is partially etched as illustrated in  FIG. 2 . Therefore, the entire thickness and surface state of the n-type GaN layer  103  are not uniform. Furthermore, if the n-type transparent electrode  108  or the n-electrode  110  are formed on the n-type GaN layer  103  whose surface is damaged, the contact resistance and the operating voltage of the electrode contacting the n-type GaN layer  103  is increased, resulting in the degradation of the luminous efficiency. 
     SUMMARY OF THE INVENTION 
     An advantage of the present invention is that it provides a vertical GaN-based LED that can prevent the damage of an n-type GaN layer contacting an n-electrode. Thus, the vertical GaN-based LED can stably secure the contact resistance of the n-electrode, reduce the operating voltage, and improve the luminous efficiency. 
     Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     According to an aspect of the invention, a vertical GaN-based LED includes: a support layer; a p-electrode formed on the support layer; a p-type GaN layer formed on the p-electrode; an active layer formed on the p-type GaN layer; an n-type GaN layer for an n-type electrode contact, formed on the active layer; an etch stop layer formed on the n-type GaN layer to expose a portion of the n-type GaN layer; and an n-electrode formed on the n-type GaN layer exposed by the etch stop layer. 
     According to another aspect of the present invention, the etch stop layer is formed of material having an etching selectivity different from that of the n-type GaN layer. 
     According to a further aspect of the present invention, the etch stop layer is formed of at least one material selected from the group consisting of group III-V semiconductor compounds, group III-VI semiconductor compounds, and group III-VII semiconductor compounds. 
     According to a still further aspect of the present invention, the etch stop layer has an uneven surface. 
     According to a still further aspect of the present invention, the vertical GaN-based LED further includes an n-type transparent electrode and an n-type reflective electrode sequentially formed between the n-type GaN layer including the etch stop layer and the n-electrode. 
     According to a still further aspect of the present invention, a method of manufacturing a vertical GaN-based LED includes: sequentially forming an undoped GaN layer, a lightly doped n-type GaN layer, an etch stop layer, an n-type GaN layer for an n-type electrode contact, an active layer, and a p-type GaN layer on a sapphire substrate; forming a p-electrode on the p-type GaN layer; forming a support layer on the p-electrode; removing the sapphire substrate using a laser lift-off (LLO) process; etching the undoped GaN layer and the lightly doped n-type GaN layer; selectively etching the etch stop layer to expose at least a portion of the n-type GaN layer; and forming an n-electrode on the exposed n-type GaN layer. 
     According to a still further aspect of the present invention, the lightly doped n-type GaN layer has a doping concentration of 10 −8 E or less. 
     According to a still further aspect of the present invention, the etch stop layer is formed of material having an etching selectivity different from that of the lightly doped n-type GaN layer and the n-type GaN layer. 
     According to a still further aspect of the present invention, the etch stop layer is formed of at least one material selected from the group consisting of group III-V semiconductor compounds, group III-VI semiconductor compounds, and group III-VII semiconductor compounds. 
     According to a still further aspect of the present invention, the method further includes forming the remaining etch stop layer to have an uneven surface after the selective etching of the etch stop layer. 
     According to a still further aspect of the present invention, the method further includes sequentially forming an n-type transparent electrode and an n-type reflective electrode on the etch stop layer and the n-type GaN layer prior to the formation of the n-type electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIGS. 1A to 1D  are sectional views illustrating a method of manufacturing a vertical GaN-based LED according to the related art; 
         FIG. 2  is a sectional view for explaining the problems of the related art; 
         FIGS. 3 and 4  are sectional views of a vertical GaN-based LED according to an embodiment of the present invention; and 
         FIGS. 5A to 5E  are sectional views illustrating a method of manufacturing a vertical GaN-based LED according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. 
     Structure of Vertical GaN-Based LED 
       FIGS. 3 and 4  are sectional views of a vertical GaN-based LED according to an embodiment of the present invention. 
     Referring to  FIG. 3 , a support layer  207  is formed in the lowermost portion of the vertical GaN-based LED. The support layer  207  supports the LED and serves as an electrode. 
     A plating seed layer (not shown) and a p-electrode  206  are sequentially formed on the support layer  207 . A p-type GaN layer  205  and a GaN/InGaN active layer  204  with a multi-quantum well structure are sequentially formed on the p-electrode  206 . It is preferable that the p-electrode  206  is formed of a metal having high reflectivity so that it can serve as both an electrode and a reflection plate. In addition, light is emitted from the active layer  204 . Generally, the active layer  204  is grown to a thickness of about 1,000 Å at a temperature of 700-900° C. An n-type GaN layer  203  for an n-type electrode contact is formed on the active layer  204 . An etch stop layer  300  exposing a portion of the n-type GaN layer  203  is formed on the n-type GaN layer  203 . 
     The etch stop layer  300  is formed of material having an etching selectivity different from that of the n-type GaN layer  203 . It is preferable that the etch stop layer  300  is formed of at least one material selected from the group consisting of groups III-V semiconductor compounds, group III-VI semiconductor compounds, and group III-VII semiconductor compounds. 
     An n-type transparent electrode  208  for improving the current spreading effect and an n-type reflective electrode  209  for improving the light efficiency are sequentially formed on the etch stop layer  300  and the n-type GaN layer  203 . An n-electrode  210  is formed on the n-type reflective electrode  209 . The formation of the n-type transparent electrode  208  and the n-type reflective electrode  209  may be omitted. In this case, the n-electrode  210  may be formed such that it directly contacts the n-type GaN layer  203  exposed by the etch stop layer  300 . 
     As illustrated in  FIG. 4 , the etch stop layer  300  may have an uneven profile. In this case, light emitted from the active layer  204  is scattered at several angles by the uneven surface of the etch stop layer  300 , thus increasing the luminous efficiency of the LED. 
     Method of Manufacturing Vertical GaN-Based LED 
     Hereinafter, a method of manufacturing a vertical GaN-based LED according to an embodiment of the present invention will be described in detail. 
       FIGS. 5A to 5E  are sectional views illustrating a method of manufacturing a vertical GaN-based LED according to an embodiment of the present invention. 
     Referring to  FIG. 5A , an undoped GaN layer  201  and a lightly doped n-type GaN layer  202  are sequentially grown on a sapphire substrate  200 . It is preferable that the lightly doped n-type GaN layer  202  has a doping concentration of 10 −18  E or less. An etch stop layer  300 , a heavily doped n-type GaN layer  203  for an n-type electrode contact, a GaN/InGaN active layer  204  with a multi-quantum well structure, and a p-type GaN layer  205  are sequentially formed on the lightly doped n-type GaN layer  202 . The etch stop layer  300  is formed of material having an etching selectivity different from those of the lightly doped n-type GaN layer  202  and the n-type GaN layer  203 . It is preferable that the etch stop layer  300  is formed of at least one material selected from the group consisting of groups III-V semiconductor compounds, group III-VI semiconductor compounds, and group III-VII semiconductor compounds. 
     A p-electrode  106  and a plating seed layer (not shown) are sequentially formed on the p-type GaN layer  205 . A support layer  207  is formed on the plating seed layer by electrolyte plating or electroless plating. The plating seed layer serves as a plating crystal nucleus when the plating process is performed for forming the support layer  207 . In addition, the support layer  207  supports the final LED structure and serves as an electrode. 
     Although the support layer  207  is provided with the plating layer formed using the plating seed layer as the crystal nucleus, the present invention is not limited to the plating layer. The support layer  207  may be formed of a Si substrate, a GaAs substrate, a Ge substrate, or a metal layer. Moreover, the metal layer may be formed using a thermal evaporator, an e-beam evaporator, a sputter, a chemical vapor deposition (CVD), and so on. 
     Referring to  FIG. 5B , the sapphire substrate  200  is removed using an LLO process. 
     Referring to  FIG. 5C , the undoped GaN layer  201  and the lightly doped n-type GaN layer  202  exposed by the process of removing the sapphire substrate  200  are etched. In this embodiment, the etch stop layer  300  having an etching selectivity different from that of the lightly doped n-type GaN layer  202  is provided under the lightly doped n-type GaN layer  202 . This etch stop layer  300  can prevent the n-type GaN layer  203  from being damaged during the process of etching the undoped GaN layer  201  and the lightly doped n-type GaN layer  202 . 
     Referring to  FIG. 5D , the etch stop layer  300  is selectively etched to expose at least a portion of the n-type GaN layer  203 . 
     That is, a portion of the etch stop layer  300  may be etched to expose a portion of the n-type GaN layer  203 , or the entire etch stop layer  300  may be etched to expose the entire n-type GaN layer  203 . In the former case, the etch stop layer  300  is etched to expose a region of the n-type GaN layer  203  corresponding to a region where an n-electrode  210  will be formed later. 
     Because the etch stop layer  300  has the etching selectivity different from that of the n-type GaN layer  203 , only the etch stop layer  300  can be selectively etched without damage of the n-type GaN layer  203 . 
     As illustrated in  FIG. 4 , after the process of selectively etching the etch stop layer  300 , the remaining etch stop layer  300  may have an uneven surface. In this case, light emitted from the active layer  204  so as to reach the etch stop layer  300  is scattered in several directions, thus increasing the luminous efficiency of the LED. 
     Referring to  FIG. 5E , an n-type transparent electrode  208  for improving the current spreading effect and an n-type reflective electrode  209  for improving the light efficiency are sequentially formed on the etch stop layer  300  and the n-type GaN layer  203 . Then, an n-electrode  210  is formed on the n-type reflective electrode  209 . 
     The process of forming the n-type transparent electrode  208  and the n-type reflective electrode  209  can be omitted. In this case, the n-electrode  210  may be formed such that it directly contacts the n-type GaN layer  203  exposed by the remaining etch stop layer  300 . 
     As described above, the etch stop layer  300  having a different etching selectivity different from the lightly doped n-type GaN layer  202  and the n-type GaN layer  203  is further formed therebetween. Therefore, the etch stop layer  300  can prevent the n-type GaN layer  203  from being removed or removed during the process of etching the lightly doped n-type GaN layer  202 . 
     Consequently, the present invention can stably secure the contact resistance of the n-type transparent electrode  208  or the n-electrode  210  formed on the n-type GaN layer  203  and can reduce the operating voltage. 
     Moreover, by forming the etch stop layer  300  to have the uneven surface, the light that is emitted from the active layer  204  and reaches the etch stop layer  300  is scattered in several directions, thus increasing the luminous efficiency of the LED. 
     Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.