Gul, Y; (2018) Spin Dependent Transport in Semiconductor Nanostructures. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This project investigates transport properties of electrons and holes con- fined into one-dimensional regions using lithographically patterned surface gates in In0.75Ga0.25As and p-type Ge quantum wells respectively. A series of transport experiments was conducted to investigate many body effects in electrons and holes in one dimension. The experimental results provided here show important advances in both In0.75Ga0.25As and p-type Ge quan- tum wires and lays the ground work for future experiments for spintronics research using these materials. The first experiments reported here (chapter 4) describes the experiments carried out to optimise fabrication methods and determine the ideal length scales of split gates to observe clear ballistic transport features in high mobility In0.75Ga0.25As wafers. The following chapter (chapter 5) summarises the one dimensional trans- port measurements carried out on narrow split gates fabricated on the high mobility In0.75 Ga0.25 As quantum wells. It explores how Rashba spin or- bit coupling effects the transport properties. In In0.75Ga0.25As a weaker backscattering due to the time-reversal asymmetry in the one-dimensional channel results in enhanced ballistic transport characteristics with clear quantised conductance plateaus up to 6(2e2/h). We investigate the con- ductance data when a d.c. voltage is applied to the source and the drain contacts and a method for obtaining the effective g factor is described. Chapter 6 introduces p-type Ge, and summarises one dimensional transport properties of these devices. We demonstrate quantised conductance up to 10 (2e2/h). Applied source-drain voltages and symmetric gating of the channel has uncovered plateau at half integer values as well as ballistic structure down to 0.25(2e2/h). These systems also show a ballistic plateau at 0.25 (2e2/h), when the carrier density is reduced using a top gate electrode. The last experimental chapter (chapter 7) analyses the many-body effects observed in one-dimensional transport measurements in p-Ge and analysis of anomalous 0.25 (2e2/h) plateau is provided with possible explanations for it. We have also shown that we can alter the confining potential using lateral gate voltages to create a row formation as the ground state effectively creates a Wigner lattice.

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