In-situ optical monitoring of surface morphology and stoichiometry during GaN metal organic vapor phase epitaxy

Abstract

The surfaces during GaN metalorganic vapor phase epitaxy (MOVPE) were in-situ monitored by shallow-angle reflectance using ultraviolet (uv) light and were compared between the growths on sapphire and on 6H–SiC substrates. By this method, stable monitoring is possible without an influence of strong and visible black-body radiation from the substrate heated to high temperatures. The growth-rate was successfully monitored by optical interference, and the morphological change was detected by the reflectivity change due to Rayleigh scattering. The surface of AlN buffer layer deposited on the (0001) sapphire substrate roughens at the thickness thinner than 30 nm, when the temperature is raised to the growth temperature of GaN. From the period of interference oscillation observed, the growth-rate on the (0001) SiC substrate is almost constant but, on the sapphire substrate, the growth-rate is about 14% decelerated in the thickness range approximately from 70 to 140 nm due to the coalescence of islands by lateral growth. Surface photoabsorption (SPA) was applied to monitor the chemical stoichiometry of GaN surface during growth. It is found that the uniform growth dominated by step-flow mode is achieved by Ga-rich stoichiometry in H 2 carrier gas. The surface process during uniform growth of GaN is also proposed.