Barrier heights of GaN Schottky contacts

Abstract

Silver and lead contacts prepared by evaporation onto clean n-GaN(0001) surfaces are rectifying. Their zero-bias barrier heights and ideality factors were determined from the current-voltage characteristics. The observed linear correlation between the barrier heights and the ideality factors is attributed to nonuniform distributions of barrier heights along the interfaces. The barrier heights of ideal Schottky contacts depend on the applied voltage due to the image-force lowering only and their ideally factors n if are approximately 1.01. By extrapolation of our experimental data to n = 1.01, we obtain barrier heights of 0.82 eV and 0.73 eV for uniform Ag- and Pb/n-GaN(0001) contacts, respectively. By applying the idea of metal-induced gap states (MIGS), the barrier heights of ideal Schottky contacts have been predicted to vary linearly as a function of the difference of the metal and the semiconductor electronegativities. The zero-charge-transfer barrier height and slope parameter are characteristic of the respective semiconductor. The zero-charge-transfer barrier heights have been calculated using an empirical tight-binding approach and the slope parameters are given by the optical dielectric constants. The experimental barrier heights of GaN Schottky contacts confirm the predictions of the MIGS-and-electronegativity model.