Sub-micron lithography using InGaN micro-LEDs: mask-free fabrication of LED arrays

The fabrication of gallium-nitride (GaN)-based light-emitting diode (LED) arrays by a direct writing technique, itself using micron-sized LEDs (micro-LEDs), is reported. CMOSdriven ultraviolet GaN-based micro-LED arrays are used to pattern photoresist layers with feature sizes as small as 500 nm. Checkerboard-type square LED array devices are then fabricated using such photoresist patterns based on either single pixel or multipixel direct writing, and implemented as part of a completely mask-less process flow. These exemplar arrays are composed of either 450-nm-emitting 199 × 199 μm2 pixels on a 200-μm pitch or 520-nm-emitting 21 × 18 μm2 pixels on a 23-μm
pitch. Fill factors of 99% and 71.5% are achieved with optical output power densities per pixel of 5 and 20 W/cm2 at 90- and 6-mA dc-injected currents, respectively.