Current conduction mechanisms of heteroepitaxial and homoepitaxial GaN films grown by MBE

We have investigated the current conduction of homo- and heteroepitaxial GaN-based films using conductive atomic force microscopy (C-AFM) and temperature dependent current-voltage (I-V-T) measurements. For homoepitaxial film grown on an HVPE template, C-AFM shows enhanced current conduction at hillocks that are associated with screw dislocations. Local current voltage measurements indicate two different forward-bias conduction mechanisms on and off such hillocks: Poole-Frenkel and field emission, respectively. In the case of heteroepitaxial film growth on sapphire, C-AFM data do not indicate a strong correlation between topography and current conduction. I-V-T measurements of Schottky diodes show thermionic field emission at high forward bias and hopping conduction at reverse bias. KOH etching of the film improves its thermionic emission properties.