Current spreading and blocking designs for improving light output power from the vertical-structured GaN-based light-emitting diodes

In this work, use of localized Ti deposition associated with a transparent indium-zine-oxide (IZO) layer is proposed to serve as Schottky current blocking and current spreading layer, respectively. In addition, an inductively coupled plasma (ICP) mesa etching on the surface layer (n-GaN) of regular vertical-conducting metal-substrate GaN-based light-emitting diodes (VM-LEDs) is also proposed to further enhance current spreading of the device. Through a two-dimensional device simulator, the calculated results indicate that significant avoidance of the current-crowding effect under cathode contact pad could be obtained once the n-GaN layer etching depth and width, IZO thickness, and Schottky current blocking width have been optimized. In experiments, 1000 mu m x 1000 mu m GaN-based blue LEDs with an ICP mesa etching,of 250 mu m in width and 2 mu m in depth on the surface n-GaN layer, 200 mu m in Schottky current blocking width, and a 300-nm-thick IZO layer have the been successfully fabricated. As compared to the regular VM-LEDs without the use of the present technology, typical improvement in light emission uniformity and light output power by about 6% and 38% at an injection current of 350 mA have been obtained.