Ph.D Thesis


Ph.D StudentIlya Baskin
SubjectOptical and Microwave Study of Non-Equilibrium Electron;
Hole and Exciton States in GaAs Based
Quantum Heterostructures
DepartmentDepartment of Physics
Supervisors Professor Emeritus Cohen Elisha
Dr. Ashkinadze Boris
Full Thesis textFull thesis text - English Version


Abstract

I report on experimental studies of the non-equilibrium states in electron, hole, exciton and phonon systems that are induced by optical, microwave (mw) or dc field excitations in GaAs based heterostructures. These non-equilibrium states are probed by optical and mw (contactless) spectroscopy as well as by transport (contact) measurements.

Microwave induced effects resulting in photoluminescence (PL) modulation were studied in undoped quantum wells (QW) and in heterostructures containing a two dimensional electron gas (2DEG), at low temperatures (< 4 K). The samples were mw irradiated (either cw or pulses) and the induced spectral PL modulation (in steady state) and temporal PL intensity response were measured. We identify various mw-induced physical processes: electron heating, electron and exciton density changes as well as an interaction of electrons, holes and excitons with non-equilibrium acoustic phonons that are emitted by the mw-heated 2DEG.

In addition, the local properties of non-equilibrium 2DEG were probed by spatially resolved (imaging) PL spectroscopy. We directly observed (for the first time) the distribution of the electric field of magnetoplasmon standing waves excited in a laterally-confined 2DEG by mw radiation. The magnetoplasmons were imaged using spatially resolved PL spectroscopy and their dependence on an external magnetic field and 2DEG density was studied. We observed remarkable spatial oscillations of the local electric field in the samples containing a high mobility 2DEG.

The local properties of a high mobility 2DEG subjected to an increasing Hall electric field were studied. We observed a spatially non-uniform distribution of a 2DEG density across the sample under increasing Hall electric field. This density redistribution is associated with the "gating effect" of the Hall electric field that is screened by low mobility charges accumulating in the layers parallel to the 2DEG. We show that Hall-induced spatial non-uniformity of the 2DEG density distribution is expected under high dc-current bias.