Hall factor in strainedp-type dopedSi1−xGexalloy

We have calculated the Hall factor in strained p-type ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ alloy grown on (001) Si, taking into account the detailed valence-band structure. Acoustic-phonon, nonpolar optical-phonon, alloy, and ionized-impurity scattering are included. It is demonstrated experimentally that the Hall factor can be reduced by a factor of 2 when alloying Si with Ge. Theoretically we have shown that the Hall factor is significantly reduced because of the nonparabolic and nonspherical effects in the valence-band structure. The theory explains experimental results very well. It is also shown that the low-temperature Hall factor is independent of scattering mechanisms. It depends only on the energy band structure. \textcopyright{} 1996 The American Physical Society.