The effective electron mass in high-mobility SiGe/Si/SiGe quantum wells

The effective mass $m^*$ of the electrons confined in high-mobility SiGe/Si/SiGe quantum wells has been measured by the analysis of the temperature dependence of the Shubnikov–de Haas oscillations. In the accessible range of electron densities, $n_s$, the effective mass has been found to grow with decreasing $n_s$, obeying the relation $m^*/m_b=n_s/(n_s-n_c)$, where $m_b$ is the electron band mass and $n_c\approx 0.54\cdot 10^{11}$ cm$^{-2}$. In samples with maximum mobilities ranging between $90$ and $220$ m$^2$/Vs, the dependence of the effective mass on the electron density has been found to be identical suggesting that the effective mass is disorder-independent, at least in the most perfect samples.