Analysis of quantum lifetime behaviour in modulation-doped n-channel Si/Si1-xGex structures

Shubnikov-de Haas measurements between 0.06 and 1.6 K have been performed on two modulation-doped n-type Si/Si1-xGe, heterostructures, and analysed to extract the quantum lifetime. Use of the conventional Dingle formula resulted in deviations from the expected theoretical behaviour 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 term was neglected. This gave plots with the correct characteristics, and 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 to acoustic phonons.