MAGNETOTRANSPORT WITH 2 OCCUPIED SUBBANDS IN A SI(100) INVERSION LAYER

We have studied electron transport in inversion layers of high-mobilit y Si(100) samples. At high electron concentrations and temperatures be low 4.2 K, two series of Shubnikov-de Haas (SdH) oscillations have bee n observed. The temperature damping of the second series oscillations indicates that the second occupied subband belongs to the first energy level of the fourfold-degenerate ladder 0'. Samples with two occupied subbands exhibit a strong anomalous negative magnetoresistance, reach ing approximate to 25% of a zero field value at B = 12 T. The decrease of resistance is more pronounced for lower temperatures and higher el ectron concentrations. We explain this behaviour by an increase of the second subband mobility due to the freezing-out of the scattering of 0' electrons. Based on the measured periods of SdH oscillations, we co nclude that the electrons are distributed inhomogeneously beneath the sample gate.