Effect of Growth Stoichiometry on the Screw Dislocation Electrical Activity in GaN Films Grown by Molecular Beam Epitaxy

Excess Ga is found at the surface termination of pure screw dislocations in GaN films grown by molecular beam epitaxy (MBE) under Ga-rich conditions. Electrical measurements performed on these Ga-rich samples show three orders of magnitude increase in reverse bias leakage compared with samples grown under Ga-lean conditions. The correlation of transport and transmission electron microscopy (TEM) results suggest that growth stoichiometry affects the screw dislocation core structure, which in term has a significant effect on the excess reverse bias leakage. We conclude that dislocation electrical activity depends sensitively on dislocation type and growth conditions.