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.