Membrane structures containing InGaN/GaN quantum wells fabricated by wet etching of sacrificial silicon substrates

Abstract

InGaN/GaN multiple quantum wells (MQWs) emitting at 410-505 nm, with either 3 or 16 repeat periods, were grown on commercial GaN-on-silicon templates using metal organic vapour phase epitaxy. Spectroscopic and structural studies confirmed these MQWs are of similar quality to analogues grown on sapphire substrates. Wet etching of the silicon (111) substrates in HF-based solutions allowed the MQW structures to be converted into membranes up to 2 mm in diameter, suspended above macroscopic via holes. Such a fabrication step is attractive for the production of microcavities, and other forms of surface emitting laser. Several MQWs have been compared by photoluminescence and cathodoluminescence spectroscopy before and after conversion to membranes. These measurements indicated a consistent increase in luminescence intensity after substrate removal, accompanied by small redshifts in peak position. We have further demonstrated plasma etching of membrane structures from the underside, as will be used to optimise structures for optical pumping, and used atomic force microscopy to monitor associated changes in surface roughness. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.