Development of Nanopillar Arrays Nanopatterning Without Lift-Off for Transferable GaN-Based µLEDs

Abstract

The mass production of µLEDs requires an upscaling approach on 200 mm wafers, which implies the deployment of a technology that achieves zero defectivity without liftoff. In this report, Nanoimprint lithography (NIL) processing is successfully optimized for nanostructuring GaN-based Silicon-On-Insulator (SOI) substrates. The etching of SiO₂/GaN/AlN/Si/SiO₂ layers using different plasmas is conducted and multi-layer nanopillars 100–200 mm in diameter are fabricated. This approach generates zero-defect arrays of pillars, which is particularly advantageous for the growth process. In addition, the SiO₂ at the bottom of the pillar allows it to twist during the subsequent GaN regrowth, as this layer becomes soft at the growth temperature >1000 °C. This ability to deform enables a coalescence of pillars into layers with reduced dislocation density. As a result, high-quality GaN microplatelets and µLEDs are grown via a bottom-up approach based on pendeoepitaxy using metal–organic vapor phase epitaxy (MOVPE). The fabricated µLEDs have a very smooth surface with a roughness of 0.6 nm which facilitated the implementation of an easy and simple transfer protocol. Adhesive tape and metalmetal bonding, are used to bond the µLEDs onto a metal-coated silicon substrate. The reported findings offer exciting new insights into the development of high-performance displays.