Abstract:
A method for fabricating a nitride semiconductor light emitting device, and a nitride semiconductor light emitting device fabricated thereby are provided. The method includes: forming a first conductive nitride semiconductor layer on a substrate; forming an active layer on the first conductive nitride semiconductor layer; forming a second conductive nitride semiconductor layer on the active layer; and lowering a temperature while adding oxygen to the result by performing a thermal process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of co-pending application Ser. No. 11/527,672 filed on Sep. 27, 2006, which claims the priority of Korean Application No. 10-2005-0090291 filed on Sep. 28, 2005. The entire contents of each of these applications are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method of fabricating a nitride semiconductor light emitting device, and a nitride semiconductor light emitting device fabricated thereby. 
         [0004]    2. Description of the Related Art 
         [0005]    Nitride semiconductors have been receiving attention as a raw material of blue light emitting diode or blue laser diode. 
         [0006]    Such a nitride semiconductor light emitting device is grown on a sapphire substrate or a SiC substrate. Then, a polycrystalline thin film Al y Ga 1−y N is grown on a sapphire substrate or a SiC substrate at a low temperature as a buffer layer. 
         [0007]    Afterward, an n-GaN layer is formed on the buffer layer by growing an undoped GaN layer and a silicon doped n-GaN layer, or a composite structure thereof at a high temperature. Then, a magnesium Mg doped p-GaN layer is formed thereon so as to fabricate a nitride semiconductor light emitting device. A light emitting layer, which is a single quantum well structure or a multi quantum well structure, is formed as a sandwich structure between the n-GaN layer and the p-GaN layer. 
         [0008]    The p-GaN layer is formed by doping a GaN layer with Mg atoms in crystal growth. During crystal growth, Mg atoms injected as a doping source are placed at Ga locations to form the p-GaN layer. However, Mg atoms react with hydrogen gas from a carrier gas or a source. As a result, Mg—H complex is formed thereby. Therefore, the Mg atoms may become a high resistor, for example, about 10 MΩ. 
         [0009]    Therefore, a post-activation process is required after forming a p-n junction light emitting device to place the Mg atoms to Ga locations by disjoining Mg—H complex. However, the amount of carrier for light emitting in the activation process is about low 10 17 /cm 3  in the light emitting device. It is very low compared to Mg atomic concentration which is mid 10 19 /cm 3 . Therefore, it is difficult to form a resistive contact. 
         [0010]    Therefore, there are many researches in progress for overcoming the shortcomings arisen by Mg—H complex. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention provides a method for fabricating a nitride semiconductor light emitting device and a nitride semiconductor light emitting device fabricated thereby for improving electrical and optical characteristics and reliability thereof. 
         [0012]    The embodiment of the present invention provides a method for fabricating a nitride semiconductor light emitting device. The method includes: forming a first conductive nitride semiconductor layer on a substrate; forming an active layer on the first conductive nitride semiconductor layer; forming a second conductive nitride semiconductor layer on the active layer; and lowering a temperature while adding oxygen to the result by performing a thermal process. 
         [0013]    The embodiment of the present invention provides a nitride semiconductor light emitting device including: a first conductive nitride semiconductor layer; an active layer formed on the first conductive nitride semiconductor layer; and a second conductive nitride semiconductor layer formed on the active layer, wherein the second conductive nitride semiconductor layer is thermal processed by reducing temperature while adding oxygen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic view illustrating a stacking structure of a nitride semiconductor light emitting device according to an embodiment of the present invention; 
           [0015]      FIG. 2  is a flowchart for describing a method for fabricating a nitride semiconductor light emitting device according to an embodiment of the present invention; and 
           [0016]      FIG. 3  is a graph showing the characteristics of a nitride semiconductor light emitting device according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    It will be understood that when an element such as a layer, film, region, pattern, structure, or substrate is referred to as being “on” another element or to as being “under” another element, it can be directly on or under the other element or intervening elements may also be present (i.e. “indirectly”). 
         [0018]    Hereinafter, the embodiment of the present invention will be described with reference to accompanying drawings. 
         [0019]    A method for fabricating a nitride semiconductor light emitting device according to an embodiment of the present invention will be described with reference to  FIGS. 1 and 2 .  FIG. 1  is a schematic view illustrating a stacking structure of a nitride semiconductor light emitting device according to an embodiment of the present invention, and  FIG. 2  is a flowchart for describing a method for fabricating a nitride semiconductor light emitting device according to an embodiment of the present invention. 
         [0020]    In the fabricating method according to the present embodiment, a first conductive nitride semiconductor  15  is formed on a substrate  11  in operation S 201 . 
         [0021]    The first conductive nitride semiconductor layer  15  may be formed as an n-GaN layer. In this case, a buffer layer  13  may be formed on the substrate  11 , and then the first conductive nitride semiconductor layer  15  may be formed on the buffer layer  13 . 
         [0022]    Herein, the buffer layer  13  may be formed as one selected stacking structures from AlInN/GaN, In x Ga 1−x N/GaN, and Al x In y Ga 1−(x+y) N/In x Ga 1−x N/GaN. As the first conductive nitride semiconductor layer  15 , an indium doped GaN layer may be employed. Also, the indium doped GaN layer with Si—In co-doped GaN formed above may be employed as the first conductive nitride semiconductor layer. 
         [0023]    Then, an active layer  17  is formed on the first conductive nitride semiconductor layer  15  in operation S 203 . Herein, the active layer  17  may be formed to have single quantum well structure or multi quantum well structure. For example, the active layer  17  may be formed of an InGaN well layer and an InGaN barrier layer. 
         [0024]    Then, a second conductive nitride semiconductor layer  19  is formed on the active layer  17  in operation S 205 . 
         [0025]    The second conductive nitride semiconductor layer may be formed as a p-GaN layer, and it functions a corresponding roll to the first conductive nitride semiconductor layer  15 . Herein, the second conductive nitride semiconductor layer  19  may be formed through magnesium Mg doping. 
         [0026]    Herein, the second conductive nitride semiconductor layer  19  may be formed as a structure where the Mg doping amount gradually increases. Also, the second conductive nitride semiconductor layer  19  may be formed as a multi-layer structure where the Mg doping amount increases step by step. For example, the second conductive nitride semiconductor layer  19  may be formed as a three-layer structure where the Mg doping amount varies in three steps. 
         [0027]    Also, the second conductive nitride semiconductor layer  19  may be grown at about 500 to 2500 Å of thickness in about 900 to 1020° C. 
         [0028]    Afterward, a thermal process is performed to add oxygen while lowering the temperature in operation S 207 . 
         [0029]    Herein, the thermal process may add oxygen to the resulting in a N 2  atmosphere while lowering the temperature. Such a thermal process reduces the Mg—H complex formed at the second conductive nitride semiconductor layer  19 . 
         [0030]    As described above, the fabricating method according to the present embodiment can improve the electrical and optical characteristics of the nitride semiconductor light emitting device. 
         [0031]    In the thermal process, the temperature is dropped to a room temperature, and about 10 to 30 cc of oxygen is added. The characteristics of nitride semiconductor light emitting device will vary as shown in  FIG. 3  through controlling the amount of oxygen.  FIG. 3  is a graph showing the characteristics of a nitride semiconductor light emitting device according to an embodiment of the present invention. 
         [0032]    The fabricating method according to the present embodiment removes the high contact resistance generated by low Mg doping efficiency of the second conductive nitride semiconductor layer  19  and removes the current crowding around an electrode, which is caused by the high contact resistance. Therefore, the fabricating method according to the present embodiment increases the carrier concentration of the second conductive nitride semiconductor layer  19 . 
         [0033]    Meanwhile, in the nitride semiconductor light emitting device according to the related art, the carrier concentration of the n-GaN layer is about (mid)×10 18 , and the carrier concentration of the p-GaN layer is very low, for example, about (low)×10 17 . Such a low carrier concentration reduces the amount of carriers injected into a quantum well. Accordingly, the light emitting efficiency is reduced and the high driving voltage is required in the nitride semiconductor light emitting device according to the related art. 
         [0034]    However, the fabricating method according to the present embodiment can increase the carrier concentration up to two times through the thermal process that adds a small amount of oxygen while reducing the temperature after growing the second conductive nitride semiconductor layer  19 . 
         [0035]    The Mg—H complex is a defect that disturbs Mg to act as a free carrier. Meanwhile, as described above, the carrier concentration of the second conductive nitride semiconductor layer, for example, p-GaN layer, increases by adding the small amount of oxygen. It is because the added oxygen O 2  is combined with H for out-diffusion. As a result, the Mg—H complex at the second nitride semiconductor layer, for example, the p-GaN layer, is reduced. 
         [0036]    As described above, a nitride semiconductor light emitting device fabricated by the method for fabricating a nitride semiconductor light emitting device of the present invention may be improved electrical and optical characteristics and reliability.