Influence of growth temperature on surface morphologies of GaN crystals grown on dot-patterned substrate by hydride vapor phase epitaxy

This paper studies the influence of growth temperatures in the range 825 to 1050°C on the surface morphologies of GaN crystals grown on a SiO ₂ dot-patterned substrate using Epitaxy Lateral Overgrowth (ELO) and Hydride Vapor Phase Epitaxy (HVPE) techniques. A lower growth temperature of 850°C prompts the formation of GaN hexagonal pyramidal crystals with a higher fraction of Fcet areas than those grown at high temperatures (>1000°C). In a subsequent coalescent (or lateral growth) process, a high temperature of 1050°C is applied to the original GaN hexagonal pyramidal crystals, and the morphologies of the GaN layers are inspected. It is established that the original morphology of the hexagonal pyramids changes to an irregularly-shaped surface comprising overline 2 s, and that the nature of the surface morphology is influenced by the growth time and the application (or not) of Ga precursor support. Hence, the results show that the coalescence and planarization of the GaN layer can be controlled through an appropriate specification of the process parameters. At low temperatures in the region of 850°C, high index facets are observed on the tops of a small percentage of the hexagonal GaN columnar crystals. It is proposed that this phenomenon is caused by a reduction in the surface diffusion length of the precursors, e.g. NH₃ and GaCl, at lower temperature, which in turn, reduces the probability of desorption and increases the lifetime.