Electronic, Transport, and Optical Properties of Broken-Gap Heterostructures

Abstract: This thesis examines the physical properties of broken-gap heterostructures using a multiband k.p model and self-consistent calculations. Broken-gap heterostructures, made from InAs, GaSb, and AlSb, are characterized by a special band alignment with an overlap between the InAs conduction band and the GaSb valence band. The band overlap results in anticrossing regions in the energy dispersions and hybridization of electrons and holes. After a summary in Swedish, intended for the general public, and an introduction, seven original papers follow. Paper 1 reviews the understanding of broken-gap heterostructures prior to this thesis. Papers 2-7 improve and extend this understanding by considering different physical properties and by using more sophisticated models. Paper 2 demonstrates the importance of lattice-mismatch-induced strain and bulk anisotropy on interband transport in tunneling structures. The choice of substrate not only alters the number of peaks in the transmission spectra, but also affects the current-density magnitude. Paper 3 considers interband tunneling under a quantizing magnetic field. The spin polarization of the tunneling current can be considerable, making these structures possible spin filters. In Paper 4, a spin polarization of the electron-hole gas in an asymmetric quantum well is generated by a lateral dc current. The sign of the spin polarization, determined by the layer widths, change as the system changes from a normal semiconductor to a hybridized semiconductor. Paper 5 considers the magnetic-field-dependence of cyclotron masses and g-factors of hybridized quantum-well eigenstates. Characteristic discontinuities appear at the anticrossings where also the g-factor's sign can change. Paper 6 also considers interband transport, but focuses on the bias threshold. It is proposed that the strength of a magnetic field can tune the transport between an Ohmic and a resonant-tunneling behavior. Paper 7 considers optical transitions induced by linearly polarized light. The reduced crystal symmetry at the interfaces, the bulk inversion asymmetry, and the electron-hole hybridization allow additional optical transitions between the quantum-well subbands.