| In this dissertation, both physics and practical aspects of various coherent phenomena in novel electronic and optical devices are investigated. The emphasis of the dissertation lies in the exploiting the similarities in the behavior of the confined optical fields and confined wavefunctions in heterostructures, in order to propose a number of novel electronic and optical devices with advantageous properties.; In Chapter two, a theory of a resonant tunneling through a quantum wire placed in transverse electric field is developed. It is found that high-gain transistor action can be caused via the electric-field-induced change imposed on the symmetry of electron wavefunctions. The current-voltage characteristics, transconductance and speed of the proposed device are evaluated. Further improvement of the device performance is done via bandgap engineering.; In Chapter three, the modulation of the wavefunction symmetry in the heterostructures finds another application—this time an electrooptical one. The principle and design of the electroabsorption modulator around 400 run using GaN/InGaN multiple quantum wells are presented. The properties of the device are theoretically calculated. The applications of the devices are discussed.; In Chapter four, the emphasis shifts to the confined optical wave, a new method of phase matching in nonlinear waveguides is proposed. It is found that high conversion efficiencies can be achieved using the higher-order waveguide mode as an intermediary for efficient second-harmonic or difference-frequency generation. The potential applications of this scheme as wavelength converter are discussed.; Chapter five takes us deeper into the field of coherent interactions in waveguides as, a novel scheme for generation of mid-infrared radiation in nonlinear waveguides with high absorption in that wavelength range is proposed. Coupling the highly-absorbing nonlinear waveguide to a linear waveguide with low absorption allows the mid-infrared radiation to escape before absorption sets in. The frequency conversion efficiency is enhanced by as much as an order of magnitude. |
