Coalescence during epitaxial lateral overgrowth of (Al,Ga)N(11.2) layers

Abstract

Epitaxial lateral overgrowth (ELOG) is reported for semi-polar (Al,Ga)N(11.2) layers on GaN/m-sapphire templates. The mask pattern consisted of periodic stripes of SiO2 oriented parallel to either the GaN[11.0] or the GaN[11.1] direction. Lateral growth occurred predominantly either unilaterally along GaN[11.1] or bi-laterally along GaN[11.0]. For growth along the [11.0]-direction, coalescence of the initial GaN domains was achieved for layer thicknesses > 4 m. However, planarization was not observed and, therefore, the resulting surface remained extremely corrugated. For lateral growth in [11.1]-direction, coalescence of initial GaN domains was delayed by a diminishing lateral growth rate as the domains converged. Insertion of an AlGaN layer during ELOG resulted in rapid coalescence to a contiguous layer. Superior crystal quality of such buffer layers as compared to conventional GaN buffer layers for the growth of InGaN/GaN quantum wells was demonstrated by photoluminescence spectroscopy.