Nonlinear optical studies of relaxation in semiconductor microstructures
Exposing a semiconductor to optical radiation near the fundamental band gap results in the creation of populations or elementary excitations including electrons, holes, and excitons, and also results in the creation of a superposition state between the ground and excited state of the solid. The relaxation of optically generated excitons and carriers in semiconductor microstructures was studied using four wave mixing (FWM) spectroscopy. The systems studied include CdSSe microcrystallite doped glasses and GaA/AlGaAs multiple quantum well structures (MQWS). First, the nonlinear optical response of simple two level systems is examined in order to provide insight into the types of line shapes expected from semiconductors. It is shown that the line shape is strongly dependent on how the system is coupled to the reservoir and the consequences of coupling to a reservoir are examined in a FWM measurement made in atomic sodium. The first semiconductor system studied is CdSSe microcrystallite doped glass. This system is shown to have a very slow component to the nonlinear response which has an optical intensity dependence and temperature dependence which suggests that the FWM response in these materials is trap mediated. Room temperature FWM measurements in GaAs MQWS enables the measurement of the carrier recombination time and the ambipolar diffusion coefficient. Using the technique of correlated optical fields, a slow component to the nonlinear response was measured showing an interference profile which suggests a possible shift of the exciton resonance due to the optically generated carriers. At low temperatures, measurements of the exciton line shape and relaxation time were made and evidence for exciton spectral diffusion was found. The low temperature line shapes can be qualitatively reproduced using Modified Optical Bloch equations which include the effects of spectral diffusion.
- Research Organization:
- Michigan Univ., Ann Arbor, MI (USA)
- OSTI ID:
- 5762709
- Resource Relation:
- Other Information: Ph.D. Thesis
- Country of Publication:
- United States
- Language:
- English
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GALLIUM ARSENIDES
ENERGY LEVELS
OPTICAL PROPERTIES
RELAXATION
AMBIPOLAR DIFFUSION
DIFFUSION
MICROSTRUCTURE
SEMICONDUCTOR MATERIALS
TEMPERATURE DEPENDENCE
ARSENIC COMPOUNDS
ARSENIDES
CRYSTAL STRUCTURE
GALLIUM COMPOUNDS
MATERIALS
PHYSICAL PROPERTIES
PNICTIDES
360603* - Materials- Properties