An unusual nonlinearity in current-voltage curves of a bidimensional electron gas at low temperatures

Abstract

Electrical characterization of a bidimensional electron gas transport has been investigated. Three AlGaAs∕GaAs heterostructures have been used for the study. Hall measurements have been performed at 4.2K and current-voltage characteristics at fixed temperatures between 4.2 and 300K. Measurements have been made using a four-point probe method. A saturation of the current at weak electric fields was observed in the range of low temperatures (<100K). The channel conductivity, the contact resistance, the electron mobility and the bidimensional electron gas density were determined. Electron drift velocities were deduced from current-voltage curves at the beginning of the saturation regime at 4.2K and compared with those found in the literature. The saturation, giving weak velocity, is related to impurity and alloy scatterings. Drift velocities close to the Fermi velocity are related to the Gunn effect. A Schottky effect has been observed at low temperatures (<100K) when the electron transport is perpendicular to the direction leading to the saturation of the current. This Schottky behavior indicates degradation of Ohmic contacts in the Au∕Ni∕Ge structure constituting the source and the drain.