Hall factor and drift mobility for hole transport in strained Si1−xGex alloys

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Abstract
Hole transport in B-doped strained Si1−xGex has been studied using Hall measurements for boron concentrations from 2×1018 to 7.5×1018 cm−3 with Ge content 0⩽x⩽0.36. By keeping the B flux constant during the molecular beam epitaxy growth of sets of samples and only varying the Si and Ge fluxes, we were able to prepare samples for an accurate determination of the Hall factor based on using the established relationship between B-doping concentration and resistivity for pure Si. It was found that the Hall factor drops considerably when the Ge content is increased. Determined Hall factor values are compared with calculated values taking into account the full valence band structure and various scattering mechanisms. The hole drift mobility has been derived from our measured Hall mobility using the determined Hall factor for the corresponding Ge content. We find that, depending on the doping concentration, the drift mobility can be higher for strained layers containing Ge. The grown layers were also characterized using x-ray diffraction, where the Ge contents and layer thicknesses could be confirmed. Temperature dependent measurements from 50 K to room temperature have also been made.