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Electron transport in InSb/AlInSb semiconductor heterostructures
[Thesis]. Manchester, UK: The University of Manchester; 2011.
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Abstract
InSb has the lowest bulk electron effective mass and the narrowest band gap of the III-V semiconductors, as well as a large dielectric constant and Lande g-factor, as a result of strong spin orbit coupling. These properties make it an exciting candidate for many different applications including high speed electronics and spintronics.This thesis presents a series of investigations on InSb/AlInSb quantum well (QW) heterostructures. The nature of transport through samples is characterised using magneto-transport measurements including Hall measurement, quantum Hall measurement, and Shubnikov de Haas oscillations. The QW 2 dimensional electron gas (2DEG) carrier densities and mobilities are extracted along with carrier densities and mobilities for transport parallel to the 2DEG. The mobilities are explained in terms of the various scattering mechanisms postulated to be present. The importance of thermally generated carriers in the lower AlInSb barrier material and the role of screening by carriers within the delta-doping plane are considered. A surface gate incorporating a gate dielectric is shown to significantly modify the transport properties and results in an increased mobility over ungated structures with the same carrier density.The measurement and analysis of transport into a 2DEG (Schottky barrier) is also presented and this transport modelled in the thermionic emission regime (by incorporation of an ideality factor) and the tunnelling regime. Gate electrodes are then used to confine the electrons in the 2DEG further to 1D. Conductance measurements are presented on split gates, demonstrating well formed conductance quantisation steps. The sensitivity of the steps presented suggest that split gates on InSb/AlInSb heterostructures could make suitable charge detectors in an electron spin qubit, an application which pushes InSb into being a practical candidate for quantum information devices.