| Wide bandgap semiconductor light emitters hold great potentials in optical data storage, bright full color display, high-speed laser printing, medical and other diagnostics. In this thesis, we present our studies on two types of wide bandgap semiconductors, namely the II-VI ZnSe-based heterostructures and III-V GaN-based materials.; With II-VI ZnSe-based heterostructures, we have employed linear and non-linear optical spectroscopic measurements to investigate the exciton physics. Optical measurements such as absorption, photoluminescence, and photoluminescence excitation experiments have revealed the important role excitons play in a quasi-2D ZnSe/ZnSSe quantum well (QW) system under low excitation conditions. Important parameters like the excitonic binding energy, excitonic radiative decay time, homogeneous broadening, etc have been obtained. We have also studied the nonlinear optical properties of exciton system under high optical excitation conditions by degenerate four-wave-mixing (DFWM) experiments. Coherence dephasing and quantum beats between the exciton and biexciton resonances have been observed. Especially, by employing a co-circular polarization configuration in DFWM experiment, we have observed the “anti-bound” states of exciton pairs in the negative pump-probe time delay window, which strongly indicates that many-body interactions are playing a crucial role in dynamics of this nonlinear exciton-biexciton system.; On III-V InxGa1−xN/GaN multiple quantum well (MQW) based light emitters, our integrated research on epilayer design, device fabrication, and device characterizations have led us to the realization of ridge-waveguide edge emitting lasers, optically pumped violet and near ultraviolet vertical cavity surface emitting lasers, and resonant cavity light emitting diodes with novel device geometry. The Henry's method based upon the fundamental correlation of spontaneous emission, stimulated emission and absorption has been adopted to analyze the gain spectroscopy of the InxGa 1−xN/GaN multiple quantum well diode lasers, the unusual broadening of the gain spectrum on the low energy side indicates the existence of localized states originating from the indium-compositional-fluctuation-induced localizations in the energy bands. |
