Characterization of spin-orbit coupling in gated wire structures using Al2O3/In0.75Ga0.25As/In0.75Al0.25As inverted heterojunctions.

Gated parallel wire structures obtained from inverted-modulation-doped heterojunctions made of high-In-content metamorphic InGaAs/InAlAs were investigated. The narrowest wire width was found to be ~190nm made using electron beam lithography and reactive ion etching. Magnetotransport was measured at low temperatures. Weak anti-localization and suppression with applied negative gate voltages were observed in low-mobility wide wires (1360 nm), which were considered for a two-dimensional system. The dependence on the gate voltage of spin-orbit coupling parameters was also obtained by fitting. The parameters decreased as the negative gate voltages increased. The trend might originate not from the electron system at the InGaAs/InAlAs interface but from the other electron system accumulated at the Al2O3/InGaAs interface, which can also contribute to conductivity. In high-mobility narrow wires (190 nm), which are close to a one-dimensional system, weak anti-localization peaks were still observed, indicating strong spin-orbit coupling. In addition, the critical widths of wires corresponding to zero conductance were estimated to be <100 nm. Therefore, our metamorphic modulation doped heterojunctions seem suitable for smaller spin-FETs. [ABSTRACT FROM AUTHOR]