Epitaxial orientation and a growth model of (0 0·1) GaN thin film on (1 1 1) spinel substrate

Abstract

GaN epitaxial crystals grown on spinel (MgAl2O4) substrates by MOCVD have been researched for the optoelectronic device applications. Though sapphire substrates usually used for GaN have no cleavage plane for a mirror cavity for a current injection laser, the (111) spinel substrate has a cleavage plane which is cocleaved with the (00·1) GaN epicrystal. The epitaxial relationship is cleared by precession photographs as follows: [100]GaN‖[011̄]spinel, [010]GaN‖[1̄01]spinel. The crystal growth model is presented on the basis of crystal chemistry and the structural stability was checked by Pauling's valence sum rule. The hexagonal closest packing structure of the O2− ions in the spinel is continued by that of the N atoms in GaN. Excess static electricity of oxygen on the surface of the spinel is held as neutrality with less valence of nitrogen on the first layer of GaN growth. The surface nitration and the cleavage for a mirror cavity are also discussed.