1. Field of the Invention
This invention relates to enhancing light extraction from high brightness light emitting diodes (LEDs).
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
It has been reported that transparent conductive oxide (TCO) films consisting of indium-tin-oxide (ITO) [1,2], Zinc Oxide (ZnO) [3], or aluminum-doped-zinc-oxide (AZO) [4] improve external quantum efficiency when applied to the surface of GaN LEDs. In addition, it has been shown that low temperature aqueous deposition can be used to fabricate ZnO current spreading layers on GaN LEDs, see [11]. Compared to a conventional thin metal current spreading layer, the ZnO layer deposited from low temperature aqueous solution improved light power output by over 90%. It has also been shown that several methods of transparent conductive oxide (TCO) layer surface roughening can also improve light extraction from LEDs [5,6]. However, all of this prior research has been conducted using TCO layers deposited only on Ga faced c-plane, p-type GaN surfaces of LEDs.