![]() The current-voltage characteristics, transconductance and speed of the proposed device are evaluated. ![]() ![]() It is found that high-gain transistor action can be caused via the electric-field-induced change imposed on the symmetry of electron wavefunctions. In Chapter two, a theory of a resonant tunneling through a quantum wire placed in transverse electric field is developed. 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. In this dissertation, both physics and practical aspects of various coherent phenomena in novel electronic and optical devices are investigated. It was the internal electric field near the heterointerfaces strongly enhanced the electro-modulation efficiency. Compared with the numerically calculated quantum state energies and wave functions, the electromodulation enhanced transitions were those involving quantum states with wave functions distribute in wider regions and extend more from the InGaNAs well into the space charge region near interfaces. Particular electro-modulated spectral features corresponding to excitonic interband transitions are enhanced. ![]() More quantum states and extended wave functions in the system with strain relief GaAsN barriers due to broader and lower confinement. The MBE grown structures consist of a central InGaNAs well, GaAs barriers, and GaAsN strain compensating buffer layers of different thickness. Read moreĮlectrooptical properties of InGaNAs/GaAs quantum well structures were investigated by photoreflectance spectroscopy. Some possibilities of obtaining enhanced electro-optic coefficients in SiGe/Si heterostructures are discussed. Possible origins of these centers are discussed. Hole traps in the p-type layers have activation energies ranging from 0.029-0.45 eV and capture cross sections (σ∞) ranging from 10−9 to 10−20 cm2. Deep levels have been identified and characterized in undoped Si1-xGex alloys. Slight enhancement of luminescence is observed in disordered wells and in quantum wires made by electron beam lithography and dry etching. luminescence in the undoped quantum wells is a result of alloy disordering. No new levels, or enhancement of luminescence, from that in undoped samples, is detected in samples which are selectively doped in the well-regions, implying that the observed. We have studied the effects of Be- and B-doping on the luminescent properties of Si1−xGex/Si single and multiquantum wells. Read moreĭeep levels and luminescence in SiGe/Si heterostructures and quantum wells have been investigated. These results suggest that the present novel fabrication method of QWWs is very promising for the formation of uniform nano-meter size quantum wires without any processing damage. Furthermore, this observed red shift is in good agreement with a simple theoretical estimate of the QWW structures observed by TEM. Since the total amount of the grown material is basically the same for both structures, this peak energy shift indicates the formation of quantum-wire-like structures at the corners of multiatomic steps. The PL peak energy of the QWW structures grown on 5.0 degrees-misoriented substrates was 23 meV smaller than that of a reference QW structure on an exactly oriented substrate. Photoluminescence (PL) of QWWs was measured at 20 K. GaAs QWWs at the corners of steps accompanied by quantum wells (QWs) on the terraces were observed in cross-sectional transmission electron microscope (TEM) images. to the fact that the GaAs growth rate on AlGaAs with multiatomic steps is much larger at the corners of steps than on the terraces. Coherent multiatomic steps with extremely straight step edges were observed on GaAs and AlGaAs epitadally grown layers on vicinal substrates over a wide observation area by atomic force microscopy (AFM). GaAs/AlGaAs quantum well wires (QWWs) were successfully fabricated using multiatomic steps on GaAs vicinal substrates by metalorganic vapor phase epitaxy (MWE).
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