: Cyclotron resonance study of HgTe/CdTe-based quantum wells with both inverted and normal band structures in quantizing magnetic fields was performed. In semimetallic HgTe quantum wells with inverted band structure, a hole cyclotron resonance line was observed for the first time. In the samples with normal band structure, interband transitions were observed with wide line width due to quantum well width fluctuations. In all samples, impurity-related magnetoabsorption lines were revealed. The obtained results were interpreted within the Kane 8·8 model, the valence band offset of CdTe and HgTe, and the Kane parameter EP being adjusted.

The simultaneous splitting of lines of an interband transition and cyclotron resonance in the conduction band has been detected in the absorption spectra of HgTe/CdHgTe quantum wells with an inverted band structure in quantizing magnetic fields. It has been shown that it is due to the absence of an inversion center in the crystal, which results in the interaction between the lower Landau level of the conduction band and the upper Landau level of the valence band.

HgTe/CdHgTe quantum well (QW) heterostructures have attracted a lot of interest recently due to insights they provided towards the physics of topological insulators and massless Dirac fermions. Our work focuses on HgCdTe QWs with the energy spectrum close to the graphene-like relativistic dispersion that is supposed to suppress the non-radiative Auger recombination. We combine various methods such as photoconductivity, photoluminescence and magneto-optical measurements as well as transmission electron microscopy to retrofit growth parameters in multi-QW waveguide structures, designed for long wavelengths lasing in the range of 10–22 μm. The results reveal that the attainable operating temperatures and wavelengths are strongly dependent on Cd content in the QW, since it alters the dominating recombination mechanism of the carriers.

We report on the comparison between temperature-dependent magneto-absorption and magnetotransport spectroscopy of HgTe/CdHgTe quantum wells in terms of the detection of the phase transition between the topological insulator and band insulator states. Our results demonstrate that temperature-dependent magnetospectroscopy is a powerful tool to discriminate trivial and topological insulator phases, yet the magnetotransport method is shown to have advantages for the clear manifestation of the phase transition with accurate quantitative values of the transition parameter (i.e., critical magnetic field B_c).

The optical phonon spectra in an HgTe quantum well surrounded by CdHgTe barriers are calculated, taking into account the contribution of free electrons to the dielectric permittivity of the quantum well. It is shown that free electrons not only change the phonon spectrum, but they can also change the number of branches of the surface optical phonons. The frequencies of the electron-optical phonon collisions, the wave-vector relaxation rates, and the energy relaxation rates are calculated for different temperatures and electron concentrations. The dependencies of the momentum and energy scattering frequencies on the electron kinetic energy are found.

Electron wave functions in the conduction band of zero-gap HgCdTe alloy are calculated in the Coulomb acceptor field. The resonant-state energies are determined.