ANALYSIS OF QUANTUM LIFETIME BEHAVIOR IN MODULATION-DOPED N-CHANNEL SI SI1-XGEX STRUCTURES/

Shubnikov-de Haas measurements between 0.06 and 1.6 K have been perfor med on two modulation-doped n-type Si/Si1-xGe, heterostructures, and a nalysed to extract the quantum lifetime. Use of the conventional Dingl e formula resulted in deviations from the expected theoretical behavio ur above similar to 0.3 K. The corresponding quantum lifetime appeared to increase with temperature in the same range. The data were then re -analysed using a modified expression, in which the thermal damping te rm was neglected. This gave plots with the correct characteristics, an d a quantum lifetime which was approximately constant with temperature , as expected for ionized impurity scattering in a degenerate electron gas. A decrease in the quantum lifetime was observed above similar to 1 K, and this is attributed to increased small-angle scattering due t o acoustic phonons.