Electronic transport of low dimensional holes in induced p-type GaAs devices

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Copyright: Chen, Jason Chao-Hsuan
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Abstract
In this thesis we study low dimensional hole systems fabricated on GaAs/AlGaAs heterostructures without any modulation dopants. The electrical transports of holes in two dimensions (2D), one dimension (1D) and zero dimension (0D) are studied. Two types of field effect transistors are fabricated and studied. The first type is a semiconductor insulator semiconductor field effect transistor (SISFET) in which 1D hole wires and a hole quantum dot are studied. The second type is a metal insulator semiconductor field effect transistor (MISFET) in which devices with the ability to switch the type of charge carriers in the conduction channel between electrons and holes are fabricated (ambipolar devices). The 1D hole wires are fabricated on the crystal plane of (100). The 1D hole wires show strong Zeeman splitting when the in-plane magnetic field is applied parallel to the 1D wires, and very small Zeeman splitting when the in-plane magnetic field is applied perpendicular to the 1D wires, regardless of the crystallographic orientation ([ 011] or [011 ̅] ). This effect is different compared to 1D hole wires fabricated on the crystal plane of (311)A, where there is an interplay between anisotropies due to the low crystal symmetry and 1D confinement resulting in different Zeeman splitting measured in wires oriented in different crystallographic orientations. We then move onto the fabrication and study of a single hole transistor in a GaAs/AlGaAs heterostructure. The Coulomb blockade oscillations resulting from single hole charges tunnelling on/off the quantum dot are observed and we also measure the charging energy of the quantum dot with source-drain bias spectroscopy. The quantum dot is found to be more stable and has less electrical noise compared to a single electron transistor fabricated on silicon, and compares favourably with an electron quantum dot fabricated on a GaAs/AlGaAs heterostructure with modulation dopants. We also fabricated the first ambipolar devices on a GaAs/AlGaAs heterostructure with the MISFET design and characterised these devices at low temperatures. Firstly the charge transport of electrons and holes are compared directly in a 2D ambipolar device by measuring the density dependence of the carrier mobility. It is observed that the electron mobility can be modelled with charge scattering theories taking into account background impurity scattering, interface roughness scattering and screening. However, when the same fitting parameters are used to model the hole mobility by switching the effective mass of electrons to holes, the theory cannot fit the experimental hole mobility. Several possibilities for the deviation of the calculations are discussed but further experimental and theoretical works need to be conducted in order to determine the exact cause for this deviation. Finally we characterised ambipolar 1D wires where both electrons and holes can be measured. Ballistic transport of both types of charge carriers is observed and we compare the 1D subband spacings of electrons to holes.
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Author(s)
Chen, Jason Chao-Hsuan
Supervisor(s)
Hamilton, Alex
Micolich, Adam
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Publication Year
2012
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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