Magnetotransport study of a high mobility two-dimensional electron gas

Abstract

This thesis is focused on an experimental study of the electrical properties of a two-dimensional electron gas formed in a GaAs/AlGaAs heterostructure. Low temperature magneto-transport measurements are used to characterize the carrier density and mobility of this system. An extensive study of the temperature and current dependence of quantum-mechanical transport effects, observable at very low temperatures, is performed in the temperature range of 4.2-100 K, for measurement currents in the range of 10 nA- 100μA. The well-known decrease in the amplitude of the Shubnikov-de Haas effect, and an accompanying increase in the onset magnetic field of these oscillations, with increasing temperature, as well as a simultaneous suppression of the quantum-Hall effect, is observed. Similar behavior is found on increasing the measurement current. An analysis of the insulator to quantum Hall transition (I-QH), occurring in the two-dimensional electron gas at low perpendicular magnetic fields, is also reported, along with the results of investigations of electron heating based on the measurements of the energy-loss rate. This study shows that the direct I-QH transition does not always correspond to the onset of strong localization, with clear Shubnikov-de Haas oscillations being observed in the insulating regime. A linear dependence of the electron energy-loss rate and electron temperature in the temperature range of 4.2-40 K is determined, indicating that the main mechanism for electron energy relaxation is acoustic phonon scattering.