Cyclotron-resonance measurements onp-type strained-layerSi1−xGex/Si heterostructures

Cyclotron resonance (CR) has been used to measure the effective mass of holes in a series of p-type modulation doped ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$/Si heterostructures, in which x varies from 0.05 to 0.29, and the two-dimensional carrier density ${\mathit{p}}_{\mathit{s}}$=(0.95–5.8)×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$. The measured masses for these samples are, to the best of our knowledge, the lowest yet reported, with a mass as low as 0.21${\mathit{m}}_0$ observed in a sample with x=0.05 and ${\mathit{p}}_{\mathit{s}}$=0.95×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$. The high quality of the samples (a 4 K hole mobility of up to 1.1×${10}^4$ ${\mathrm{cm}}^2$ ${\mathrm{V}}^{\mathrm{-}1}$ ${\mathrm{s}}^{\mathrm{-}1}$) enables a clear resolution of two CR features corresponding to resonances from the lowest spin-split states, at the magnetic field where the filling factor changes from 1k⋅p model give very good agreement with the experimental observations on the x=0.05 sample, and provide a qualitative explanation of the change in mass with increasing Ge content.