Effective mass measurement: the influence of hole band nonparabolicity in SiGe/Ge quantum wells

摘要

We show that the common practice of identifying effective masses derived from Shubnikov-de Haas (SdH) and cyclotron resonance measurements with zero-field effective density of states (DOS) masses must be scrutinized when nonparabolicity effects come into play. To this end, the temperature dependence of theoretical SdH oscillations expected for strained-Ge quantum wells is explicitly simulated from calculations of the Landau level structure, giving rise to theoretical masses in exact analogy to a SdH measurement. The calculations are performed within a 6 x 6 envelope function approximation (EFA). The same method is used to calculate the zero-field DOS mass. Our analysis shows that the pronounced nonparabolicity of the heavy hole band leads to a nonlinear magnetic field dependence of Landau level energies invalidating the assumption of equal cyclotron and DOS masses. In particular, we show that at high carrier density the DOS mass is significantly underestimated in a SdH measurement.