Schottky gating high mobility Si/Si1-xGex 2D electron systems

A high mobility (3.6 x 10(5) cm(2)/V a) n-type Si/Si1-xGex heterostructure has been Schottky gated using An metal to cover the whole of the device. Ov er the front-gate voltage (V-g) range for which there was negligible gate l eakage (-0.1 V < V-g < 0.1 V), the carrier density could be varied from 1.7 x 10(11)to 4.4 x 10(11) cm(-2). Measurements of the quantum lifetime sugge sted that the quality of the device varied in a manner not indicated by the transport mobility. This may arise from inhomogeneities caused by energy-l evel broadening. The results can be explained by a surface-roughened Au gat e whose influence is negated at zero front-gate voltage due to a frozen-in screening charge in the doping layer. (C) 2000 Published by Elsevier Scienc e S.A. All rights reserved.