Optical nonlinearities in bulk, multiple-quantum-well and doping superlattice gallium-arsenide with device applications.

Abstract

The linear and nonlinear optical properties of bulk, multiple-quantum-well, and doping superlattice GaAs are investigated experimentally and theoretically, and their properties are discussed in terms of their applicability to optical bistable devices and optical logic gates. A systematic study of the room temperature, frequency-dependent optical nonlinearities of bulk and multiple-quantum-well GaAs is reported and discussed. The results of the bulk GaAs experiments are in good agreement with a recently developed plasma theory. The carrier lifetime and the optical nonlinearities of multiple-quantum-well structures of varying well sizes are measured and compared to bulk GaAs. The prospect of lowering the power threshold for nonlinear action is explored in GaAs doping superlattices. The ability to increase the carrier lifetime with internal space charge fields is demonstrated experimentally in a doping superlattice structure. The possibility of using these long lifetimes to lower the power requirements of optical bistability is discussed. The linear optical properties of quantum-confined structures are studied both in GaAs/AlGaAs quantum wires as well as in CdS quantum dots. The enhanced confinement of the carriers shifts the absorption band-edge to higher energies relative to bulk. The techniques used to fabricate these nanometer-sized features are outlined. Several optical device structures are fabricated and tested. The nonlinear reflection properties of a distributed feedback structure consisting of a GaAs/AlGaAs quarter wave stack are evaluated experimentally both from the physics and device point of view. Such a structure is used to monolithically grow a nonlinear Fabry-Perot etalon for optical bistability and optical logic gating. This integrated Fabry-Perot device is uniform over a 1 cm² area with switching characteristics comparable to the best devices previously obtained and with improved thermal stability. The fact that diode lasers can be used as light sources makes GaAs optical logic gates more attractive for optical signal processing. An all-optical NOR gate using GaAs as nonlinear optical material and diode laser as optical source is demonstrated for this purpose.