Fabrication of planar GaN-based micro-pixel light emitting diode arrays

Micro-pixelated GaN light-emitting diodes (‘micro-LED’s) offer attractions for a wide range of applications including microdisplays, mask-free photolithography, lab-on-a-chip and bioinstrumentation [1]. Mesa dry etching methods have underpinned the development of this technology to date. Here we propose and demonstrate a new planar process which simplifies the process flow and permits individually-addressable pixelated devices to be fabricated without any obvious degradation of electrical and optical performance. The approach is based on the intrinsic high resistivity of the p-type GaN layer for pixel to pixel electrical isolation and on a CHF3 plasma treatment to dramatically reduce current leakage through the p-GaN/metal interface. Consequently, this process requires a lower number of fabrication steps than previously used processes using mesa etching for pixel definition and dielectric deposition for electrical insulation [2]. It leads to a planar active area well suited for further integration of functional micro-elements, including microfluidic-channels, microoptics or luminescent materials for colour conversion [3, 4]. This new fabrication route has been validated by fabricating and characterizing an individually addressable micro-stripe LED array emitting at 470 nm.