Roles for aluminium indium nitride insertion layers in fabrication of GaN-based microcavities

AlInN alloys achieve an in-plane lattice match to hexagonal GaN at an indium nitride mole fraction of ∼18%. Meanwhile Al _0.82In _0.18N displays a refractive index contrast of ∼7% with GaN at visible wavelengths. We illustrate the use of Al _0.82In _0.18N insertion layers to control layer thicknesses during homoepitaxial growth of GaN-based microcavities, using in situ optical reflectometry. The structures discussed are 3λ/2 microcavities incorporating distributed InGaN quantum wells tailored for emission at ∼400 nm. As-grown samples have been characterised by techniques including cathodoluminescence spectroscopy. In addition to their role in growth monitoring, there are several post-growth processing steps in which Al _0.82In _0.18N insertion layers can assist microcavity fabrication. We focus here on a demonstration of the ∼1:5 etch rate selectivity obtainable between Al _0.82In _0.18N and GaN in reactive ion etching.