Calculated potential profile near charged threading dislocations at metal/semiconductor interfaces

Abstract

We have made finite element calculations of the expected potential profile around negatively charged threading dislocations (TDs) close to a metal–semiconductor interface, using a Pt contact on n-type GaN as a specific case. The potential was calculated as a function of the assumed linear density and energy level of TD-related acceptors. Our model shows good agreement with the model of Read [W. T. Read, Philos. Mag. 45, 775 (1954); 46, 111 (1954)] for an infinite dislocation, far from any interface. Assuming 1 acceptor/c-axis lattice spacing (c=0.52 nm), we found for our near-surface modeling that acceptors levels deeper than 1.3 eV below the conduction band minimum (CBM) should be charged all the way to the Pt/GaN interface. This should produce a significant local increase in the potential barrier and at the Pt/GaN interface and should be observable by ballistic electron emission microscopy (BEEM). In fact recent BEEM measurements by Im et al. on molecular beam epitaxy-grown GaN films [Phys. Rev. Lett. 87, 106802 (2001)] showed no significant increased barrier at TDs indicating an acceptor energy within 1.3 eV of CBM and/or an acceptor density less then 1 acceptor/c-axis lattice spacing.