Multiple quantum well based optoelectronic devices for systems applications.

Abstract

The quantum confinement of electrons and holes in semiconductor quantum wells leads to enhancements in the optical properties sought after in optoelectronic devices. Such confinement strengthens the effects of excitons, or hydrogenic-like states consisting of electrons and holes, at room temperature. Such states manifest themselves, optically, as sharp peaks in the absorption spectra at band edge. These peaks shift with an applied electric field, resulting in tunable absorption characteristics (the quantum confined Stark effect, QCSE). This thesis serves to demonstrate broadened usage of QCSE based multiple quantum well (MQW) devices in communications and data storage systems. In addition to such devices, based on the quantum confinement of charge carriers, novel nanofabrication technologies are developed for devices utilizing the quantum confinement of photons in microcavities. An optical cavity whose volume is on the order of a wavelength cubed in the material has an enhanced photonic density-of-states. A result of this is that photons spontaneously emitted in such a cavity will very efficiently be coupled into the dominant cavity mode, thus creating the possibility of highly efficient, and even 'thresholdless', lasers made of such microcavities. Four device concepts, based on the aforementioned quantum confinement, were experimentally investigated for systems applications. Firstly, a concept for applying the QCSE towards dual wavelength systems has been developed and applied towards creating dense memories and switches. Secondly, an MQW-based tunable wavelength-selective filter has been developed for wavelength division multiplexed (WDM) receiving applications. Using the increased electro-optic coefficient in quantum wells, a Bragg Filter is established in the waveguide by the application of a spatially periodic DC field across the wells with a Schottky metal grating atop the guide. The filter, being field tuned, offers the possibility of very high speed tunability. Thirdly, a PIN MQW-based optoelectronic architecture has been developed for optical pattern matching. This scheme is demonstrated in a packet switching application, allowing the reading of the destination address of a data packet in an optical network. Finally, two architectures for microcavity lasers, one edge emitting and one surface emitting, have been experimentally explored for low-threshold operation, using novel nanofabrication techniques. The theoretical and practical limits of these devices and their associated systems applications are discussed.