Growth of AlN on sapphire: Predicting the optimal nucleation density by surface kinetics modeling

Abstract

We report on the growth of AlN epilayers at reasonably low temperatures of 1050–1110 °C on non-miscut c-plane sapphire by metal organic chemical vapor deposition (MOCVD). A systematic study of growth parameters revealed that the thickness of the low temperature (LT) nucleation layer (NL) plays a critical role in improving the screw and edge dislocation densities and surface morphology of the AlN epilayer. A surface kinetics based physico-chemical model is proposed to optimize the crystalline quality and is found to correlate well to the experimental observations. Using a 7 nm nominally-thick LT NL, a 0.5 μm thick AlN epilayer with an rms roughness of 0.15 nm, and (002) and (102) omega scan widths of 18 arc sec and 970 arc sec, respectively, was realized. A grain coalescence model for stress generation is used to correlate the change in AlN growth stress with variation in the NL thickness, and it is shown that in-situ stress measurement can be employed as an early signature for reproducibility of the crystalline quality. This study suggests that AlN/sapphire templates can potentially be realized for a reasonably low thickness (0.5 μm) and at temperatures as low as 1050 °C, which is accessible by most of the III-nitride MOCVD systems.