Cyclotron effective mass of holes in Si_1-xGe_x/Si quantum wells: Strain and nonparabolicity effects

The Ge-composition dependence of cyclotron effective mass of quasi-two-dimensional holes in strained Si1-xGex/Si quantum well structures has been investigated by far-infrared magneto-optical spectroscopy at low temperatures and high magnetic fields up to 23 T. The in-plane effective mass determined from cyclotron resonance energies is much less than that of unstrained Si1-xGex alloys and decreases systematically from 0.40me to 0.29me as the Ge composition increases from x=0.13 to x=0.37, indicating the importance of the strain effect on the valence-band structure. The nonparabolicity correction is significant in explaining the discrepancy between the measured values and the calculated band-edge masses.