Transport, Growth Mechanisms, and Material Quality in GaN Epitaxial Lateral Overgrowth

Abstract

Growth kinetics, mechanisms, and material quality in GaN epitaxial lateral over-growth (ELO) were examined using a single mask of systematically varied patterns. A 2-D gas phase reaction/diffusion model describes how transport of the Ga precursor to the growth surface enhances the lateral rate in the early stages of growth. In agreement with SEM studies of truncated growth runs, the model also predicts the dramatic decrease in the lateral rate that occurs as GaN over-growth reduces the exposed area of the mask. At the point of convergence, a step-flow coalescence mechanism is observed to fill in the area between lateral growth-fronts. This alternative growth mode in which a secondary growth of GaN is nucleated along a single convergence line, may be responsible for producing smooth films observed to have uniform cathodoluminescence (CL) when using 1μm nucleation zones. Although emission is comprised of both UV (∼365nm) and yellow (∼550nm) components, the spectra suggest these films have reduced concentrations of threading dislocations normally associated with non-radiative recombination centers and defects known to accompany growth-front convergence lines.