High reflectance membrane-based distributed Bragg reflectors for GaN photonics

Abstract

Preparation of highly reflective distributed Bragg reflectors (DBRs) from III-nitrides is an important building block for cavity photonics. In this work, we report the fabrication of a membrane-based GaN/air-gap DBR for blue/green light emitting devices. The formation of membrane DBRs relies on a recently discovered electrochemical procedure in which selective etch is achieved by adjusting the conductivity rather than chemical composition, thus relieving greatly the burden in creating epitaxial DBRs. Micro-reflectance measurement shows over 98% peak reflectance and a wide stopband with only four pairs of GaN/air-gap layers. Micro-photoluminescence spectra of InGaN multiple quantum wells (MQWs) on DBRs show reduced linewidth and improved emission efficiency. After capping the MQWs on DBRs with silver, a significant linewidth narrowing indicates the modification of spontaneous emission due to the presence of a planar microcavity.