Microwave and terahertz studies of the electron dynamics in two-dimensional electron systems

This thesis reports the design and implementation of different experimental systems to study electron-dynamics in two-dimensional electron gases (2DEGs) at microwave and terahertz (THz) frequencies. Both time and frequency domain techniques have been used to study the transport properties of electrons in GaAs/Al- GaAs heterostructures. First of all a free-space time-domain spectroscopy (TDS)
polarisation sensitive detection system capable of measuring the full polarization state of a propagating THz electric field has been demonstrated. Polarization-
sensitive systems provide additional information on material characterization that is inaccessible through conventional techniques. The polarization sensitivity of the
THz-TDS system has been evaluated using a 0.5mm thick LiNbO3 sample. The ability to measure the rotation in polarisation caused by a sample allows measurement of direction-dependent material properties, such as the electrical conductivity of low-dimensional semiconductors displaying the quantum Hall effect, or the di-electric permitivity in anisotropic material systems. The newly designed system has been used to evaluate the magneto-conductivity of a 2DEG up to 1.4 THz and 6T. Two separate continuous-wave polarisation-sensitive free-space systems, operating at microwave and THz frequencies, have also been demonstrated. Both systems have been used to study the magneto-conductivity of a 2DEG at microwave (75{110 GHz) and THz (2.6{3.2 THz) frequencies up to a magnetic field of 8T. The continuous-wave microwave system has also been used to study the phenomenon of edge magneto-plasmons in a 2DEG. The work presented in this thesis provides a valuable groundwork to study the electron-dynamics in 2DEGs over a wide range of frequencies (both microwave and THz) and for a wide range of experimental conditions.