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Title: On-chip THz studies of low-dimensional semiconductor systems
Author: Mistry, Divyang Kishore
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2013
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A wide range of novel on-chip integration techniques were developed to explore the low-temperature perturbation of GaAs/AlGaAs based confined electron systems at terahertz frequencies. A new methodology for pump-probe transmission measurements of THz pulses along on-chip coplanar waveguides is demonstrated, allowing generation of guided THz signals and subsequent detection after propagation through in-plane integrated nanoscale devices at sub-Kelvin temperatures and under magnetic fields. Initially, several methods that demonstrate introducing a guided-wave THz signal into an embedded two-dimensional electron system (2DES), involve the assembly of discrete substrate chips containing either the THz photoconductive material or a 2DES. The introduction of novel, monolithic integration of the 2DES layer and the THz photoconductive layer into a fully integrated epitaxially grown heterostructure, allowed successful incorporation of both the 2DES and the on-chip THz waveguides onto a single chip. The independent characterisation measurements of both the incorporated systems allowed optimisation of the monolithic structure, resulting in achievement of undiminished performance for both the 2DES and the on-chip THz waveguides. A full characterisation of THz pulses interacting with an embedded 2DES, using both injected and capacitive, evanescent field coupling of the THz signal, are first performed at variable temperatures from (4 K to 300 K). It is found from the experimental observations that the temperature dependent 2DES resistivity can be directly probed from the time-domain transmitted THz pulses. Independently, a new method for sub-Kelvin excitation and detection of on-chip THz frequency radiation at temperatures as low as 200 mK and magnetic fields up to 12 T is also demonstrated, which was employed to probe the magneto conductivity of the 2DES through THz pulse injection using on-chip waveguides. The successful demonstration of THz pulse injection in low-dimensional electron systems using on-chip waveguides at sub-Kelvin temperatures and under magnetic fields paves the way for enhancing the studies of single electron transport, by investigating the properties of 1D or 0D quantum systems in the terahertz-frequency range.
Supervisor: Cunningham, John ; Linfield, Edmund ; Davies, Giles Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available