Two-dimensional electron systems in HgTe quantum wells

Abstract

A brief review is given on the results of research on the properties of two-dimensional (2D) electron systems in quantum wells based on CdHgTe∕HgTe∕CdHgTe double heterojunctions with surface orientations of (100) and (013). The main features of the energy spectrum are described. The results of experiments yielding information about the parameters of the energy spectrum are presented. From cyclotron resonance measurements the effective mass of the 2D electrons in HgTe quantum wells with inverted band structure is obtained as a function of the density of such electrons, Ns, in the range 2.2×1011cm−2⩽Ns⩽9.6×1011cm−2. This density dependence indicates an appreciable nonparabolicity of the spectrum: the mass increases with increasing Ns in that range from a value (0.026±0.005)m0 to (0.0335±0.005)m0. The giant spin splitting observed in asymmetric HgTe quantum wells is discussed, and the results of experimental research on the transition from a quantum Hall liquid to an insulator and the plateau-plateau transition in 2D electron systems in HgTe quantum wells are recounted. The 2D electron-hole system observed recently in the quantum wells under study, which is the first realization of a 2D semimetal, is described. It is found that it arises in lightly doped quantum wells with an inverted band structure and surface orientation (013). The magnetotransport is found to exhibit a number of features (positive magnetoresistance, variable-sign Hall effect, anomalous behavior in the quantum Hall effect regime) due to the simultaneous existence of 2D electrons and holes.