Magneto-optical studies of semiconductor heterostructures

Abstract

This thesis is primarily concerned with far infrared effects in semiconductor heterostructures. These properties have been studied as a function of magnetic fields at low temperature using various optical detection techniques. Cyclotron resonance has been studied in CdTe quantum wells. The results are compared with calculations using the memory function approach, which demonstrate that there is a large reduction in the resonant coupling due to level occupancy effects. Semimetallic GaSb/InAs superlattices have been studied by cyclotron resonance experiments. In samples with low InAs/GaSb ratios (~1), a pinning between the heavy hole subbands is predicted by theory which results in a suppression of heavy hole resonance at high magnetic fields. Photoluminescence measurements on a series of ultra-high mobility GaAs/AlGaAs heterojunctions have been performed. It has been found that the modulation caused by far infrared beam is entirely dependent on the filling factors, which is understood as the Landau level coupling effects between the subbands of 2DES. A GaAs/AlGaAs coupled quantum well photodiode has been studied by photoluminescence and photocurrent under the influence of far infrared beam. An enhancement of the photocurrent in the device is observed when the infrared photons are resonant with the intersubband transition between the anti-crossing electronic subbands of the coupled quantum wells, which makes the structure a potential tuneable far infrared detector. Most of the experimental works have been modelled with a k.p theory using momentum matrix approach. The self-consistency incorporated in this model proves to be useful while dealing with semimetallic or nonintrinsic systems. These calculations offer invaluable clues to the semiconductor heterostructures investigated.