Multiple Shapes Micro‐LEDs with Defect Free Sidewalls and Simple Liftoff and Transfer Using Selective Area Growth on Hexagonal Boron Nitride Template

Abstract

Several technological challenges have prevented GaN‐based micro‐LEDs from finding application in mass market displays, despite their unique properties such as very high brightness and the very fast response time of GaN‐based materials. The primary challenges are the cost and complexity of lift‐off and transfer of LEDs from sapphire substrates to suitable supports as well as the lowered performance of tiny micro‐LEDs caused by chemical etching that defines individual LEDs. Herein, this work reports demonstration of a complete process that solves these challenges with epitaxy and cleanroom technologies that are commercially available. The process begins with van der Waals epitaxy of 2D h‐BN on silica masks with square, triangular and hexagonal patterns on sapphire substrates which define the micro‐LED regions. Then selective area growth of MQW LED heterostructures, with ultra smooth crystalline sidewalls, down to ultra tiny size of 1.4 µm is performed. Because of the lack of vertical chemical bonds in the h‐BN layer, simple mechanical lift‐off and transfer is performed on an array of LEDs heterostructures down to size of 8 µm. Finally, transparent ITO p‐contacts are deposited on LEDs with uniform lift‐off, resulting in high brightness LEDs.

The micro-LED roadmap: status quo and prospects

“…Another novel defect-free sidewall method was recently reported with epitaxy and cleanroom technologies [231]. Using selective area growth of MQW LED heterostructures on hexagonal boron nitride (h-BN) template, small-size micro-LED arrays with smooth crystalline sidewalls can be produced, and the arrays can be successfully lift-off and transferred due to comparably weak vertical van der Waal forces between LED and h-BN substrate.…”