Channeling contrast microscopy on lateral epitaxial overgrown GaN

Abstract

High resolution (<1 μm) channeling contrast microscopy (CCM) is employed to map variations of crystallographic orientation across micron-sized regions of lateral epitaxial overgrown (LEO) GaN thin film structures. The sample consists of 6 μm thick GaN stripes, aligned along the [1 1 ̄ 0 0] GaN direction, grown by LEO from 3 μm wide Si 3N 4 windows spaced 13 μm apart. Axial CCM using 2 MeV He + is employed to investigate the crystalline structure of the LEO GaN layer. A low χ min of ∼2.8% and a critical angle ψ 1/2 of ∼0.85° is found, comparable with data obtained from broad beam channeling [J. Portmann, C. Huag, R. Benn, T. Frey, B. Schottker, D.J. As, Nucl. Instr. and Meth. B 155 (1999) 489]. 5 μm wide bands of high and low yield at a periodicity of 13 μm are observed in the CCM maps. This contrast is due to the opposing tilts of the [0 0 0 1] axis in the overgrown regions (the so-called wings) on either side of the window regions. From angular scan curves this tilt is found to be ±0.45° in the direction perpendicular to the GaN stripes and no measurable wing tilt is found along the stripe direction.