Study of leakage defects on GaN films by conductive atomic force microscopy

We have used the techniques of atomic force microscopy (AFM) and conductive AFM (C-AFM) to investigate the forward and reverse bias conduction properties of defects in GaN films grown by molecular beam epitaxy (MBE) on metal organic chemical vapor deposition (MOCVD) templates. The surface morphology consists of holes interspersed between undulating spiral "hillocks" terminated by pits that have been associated with screw dislocations. For C-AFM measurements, a Pt-coated AFM tip was brought into contact with the GaN surface to form a microscopic Schottky contact. Reverse-bias current leakage is observed for similar to 10% of hillocks up to 12 V, and increases to approximately 50% of both hillocks and holes for bias voltages above 25 V. Leakage sites initially occur at similar to 10 V and increase substantially in number above similar to 15 V.