Critical Roles of Decomposition-Shielding Layer Deposited at Low Temperature Governing the Structural and Photoluminescence Properties of Cubic GaN Epilayers Grown on (001) GaAs by Metalorganic Vapor Phase Epitaxy

Roles of a thin GaN layer deposited at low temperature (LT-GaN) on (001) GaAs substrates during metalorganic vapor phase epitaxy of cubic (c-) GaN were investigated in terms of crystallographic tilt, photoluminescence (PL) line width, and PL lifetime at room temperature. When the nominal LT-GaN thickness was approximately 5-7 nm, reasonable-quality epilayers were obtained, though distinct voids were formed on the substrate side of the c-GaN/GaAs interface. Lateral epitaxial overgrowth on voids was found in the cross-sectional transmission electron micrographs of those samples, and the epilayers exhibited a smaller tilt. A further decrease in LT-GaN thickness caused a destructive peeling of the epilayer due to thermal decomposition of the substrate. On the other hand, an increase in LT-GaN thickness induced mixing of hexagonal phases. In order to obtain a pure c-GaN film, the substrate decomposition-shielding LT-GaN was verified to have a simultaneous role in transmitting cubic lattice information.