Barrier Height Reduction at the Pd-Ge/n-GaAs Interface

Abstract

ABSTRACTWe present the first direct measurements showing changes in the Schottky barrier height for ohmic Pd-Ge contacts to n-type GaAs. The barrier height and interface chemistry were investigated with high resolution synchrotron ultraviolet photoemission spectroscopy. Interfaces were formed by the deposition of one layer each of Pd and Ge on the GaAs substrate, where the deposition sequence was varied to allow a more quantitative determination of the role of each element. A reduction of 0.35 eV in the barrier height occurred in the case where Pd was deposited first. This reduction can be described by a model in which interface states are compensated by charge from As n-type doping of the Ge layer in the Ge-GaAs heterojunction. The dramatic change in barrier height seen when Pd is deposited first contrasts sharply with the stable barrier height observed for the case where the Ge was deposited first, a constant barrier of 0.75 eV was found after every deposition and annealing step. This stability was correlated with constant Ga and As concentrations in the Ge and a relatively low overall As concentration in the overlayer.