Far-infrared magneto-optical study of holes and electrons in zero-band-gap HgTe/Cd0.85Hg0.15Te superlattices

Far-infrared (FIR) magnetotransmission and magnetotransport measurements have been performed on two HgTe/${\mathrm{Hg}}_{0.15}$ ${\mathrm{Cd}}_{0.85}$Te superlattices over a wide temperature region. Three of the six observed resonances are identified as cyclotron resonances of holes and electrons associated with the ${\mathrm{HH}}_1$ band, and of thermally excited electrons in the ${\mathit{E}}_1$ band. Furthermore, the temperature dependence of the electron effective mass and its anisotropy is obtained from these experiments, and an attempt is made to correlate the observed mass behavior with the temperature-induced transition of the superlattices from the zero-band-gap to the open-band-gap regime. Finally, we briefly mention two further FIR resonances observed in the course of these experiments, which are identified as the 1s→2${\mathit{p}}^{+}$ transition and as cyclotron resonance of electrons occurring in the CdTe substrate of the superlattice.