Spin-orbit coupling in Ga_xIn_(1-x)As/InP two-dimensional electron gases and quantum wire structures

摘要

In this work, the effect of spin-orbit coupling in two-dimensional electron gases and quantum wire structures is discussed. First, the theoretical framework is introduced including spin-orbit coupling due to structural inversion asymmetry, the so-called Rashba effect, as well as the Dresselhaus term. The latter originates from bulk inversion asymmetry. With regard to wire structures, special attention is devoted to the influence of the particular shape of the confinement potential on the energy spectrum. As a model system Ga_xIn_(1-x)As/InP heterostructures are chosen, where different thicknesses of the strained Ga_(0.23)In_(0.77) As channel layer were introduced, in order to adjust the strength of the spin-orbit coupling. Hall bar structures as well as sets of identical wires with different widths were prepared. In two-dimensional electron gases, the strength of the spin-orbit coupling was extracted by analyzing the characteristic beating pattern in the Shubnikov-de Haas oscillations. In addition, the weak antilocalization was utilized to obtain information on the spin-orbit coupling. It is shown that for decreasing width of the strained layer the Rashba effect, which dominates in our layer systems, is increased. This behavior is attributed to the larger interface contribution if the electron wavefunction is strongly confined. The measurements on the wire structures revealed a transition from weak antilocalization to weak localization if the wire width is decreased. This effect is attributed to an enhanced spin diffusion length for strongly confined systems.