Barrier height reduction in Au–Ge Schottky contacts to n-type GaAs

Abstract

Current–voltage (I–V) and capacitance–voltage (C–V), measurements were combined with Auger electron spectroscopy (AES) to study the effects of heat treatment on Au–Ge Schottky contacts to n-type GaAs in the temperature range below the Au–Ge eutectic point (∼360 °C). Upon deposition and heat treatment of the contacts, the data showed two distinct stages of transformation at the metal–semiconductor interface. In the first stage a small fraction of Ge atoms, formed an interface layer with an effective n-type doping of one order of magnitude higher than the initial doping of the epitaxial layer and resulted in a current transport mechanism consistent with thermionic-field emission (TFE). In the second stage, while the effective interface doping remained the same, a substantial reduction of the barrier height from φb (TFE)=0.75 eV at 250 °C heat treatment to φb (TFE)=0.34 eV at 300 °C heat treatment was evident and was attributed to the increased disorder at the interface resulting from the indiffusion of the remainder large fraction of Ge (and Au) atoms. The effects of heat treatment appeared to predominantly increase the disorder rather than the doping at the emerging ‘‘heterointerface.’’