Study of surface over-layer contribution to Dislocation Assisted Tunneling current: Strategy to improve Pt/n(+)-GaN Schottky characteristics

This paper reports the importance of surface over-layer contribution to the dislocation assisted tunnelling (DAT) current along with earlier reported bulk dislocations due to growth of GaN layers on highly lattice-mismatched substrates. This claim is substantiated by demonstrating an improved Pt/n(+)-GaN Schottky diode characteristics with the removal of surface over-layer. This is achieved by treating the n(+)-GaN layers with Buffered Oxide Etchant(BOE) before Pt deposition. The improvements are observed in three crucial aspects of Pt/n(+)-GaN Schottky diode namely turn-on voltage (V-t); dislocation assisted tunnelling (DAT) parameter (E-0), and reverse bias current. These improvements are achieved by treating n(+)-GaN surface with 1:7 BOE before Pt deposition. The DAT model adequately explains the device characteristics. Further, the dislocation density used in DAT analysis is experimentally quantified using HR-XRD. The removal of Ga2O3 and significant blue shift of Ga 3d peaks by 0.6 eV post-treatment as observed in XPS measurements, results in improved conduction of electrons at the n(+)-GaN surface and Pt/n(+)-GaN device characteristics.