Electron transport and cyclotron resonance in [211]-oriented HgTe--CdTe superlattices

We discuss a magnetotransport and magneto-optical investigation of [211]-oriented HgTe--CdTe superlattices. Measurements were performed on seven n-type samples with well widths in the range 41--125 A and energy gaps between 0 and 128 meV. Both magnetotransport and magneto-optical results give evidence for an additional electron species besides the superlattice electrons and holes usually observed. We show that although these have quasi-two-dimensional character, their mobilities are quite sensitive to the superlattice well thickness. These findings are interpreted in terms of band bending and charge transfer from the CdTe substrate into the superlattice. We also discuss the first theoretical calculations of the band structure for [211]-oriented HgTe--CdTe heterostructures