Enhancement of the light output of GaN-based light-emitting diodes using surface-textured indium-tin-oxide transparent ohmic contacts

Abstract

InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) with indium tin oxide (ITO) as widow layers were fabricated. The ITO surface was textured utilizing the natural lithography combined with the inductively coupled plasma (ICP) etching technology by use of polystyrene spheres as the etching mask. The morphologies of the textured ITO surface were characterized by a scanning electron microscope (SEM) and an atomic force microscope (AFM). The electrical and optical properties of surface-textured ITO/GaN LEDs were measured and analyzed. The influence and dependence of ICP etching time on the light output of the fabricated LEDs was investigated. Experimental results indicated that ITO/GaN LEDs with nano-islands with a depth of about 120 nm and a diameter about 320 nm on the surfaces exhibited a ∼60% or more enhancement in the output power. The typical 20 mA driven forward voltage is only 0.2 V higher than that of conventional planar ITO/GaN LED. The fabricated surface-textured GaN LED chips from the whole 2″ wafer presented a quite good conformance in electrical and optical characteristics, and the proposed method demonstrated a good reliability. The results indicate that the surface-textured ITO method utilizing the natural lithography combined with the inductively coupled plasma (ICP) etching technology has high potential in future large-area high-power GaN LED applications.