Quantum dot (QD) has been known as three-dimensional quantum confined structure. Thus, a delta-function type of density with three-dimensional coulomb interaction can have strong dependence on field-driven optical absorption, i.e. Quantum Confine Stark Effect (QCSE), leading to lots of advantages for applications of electroabsorption modulator (EAM). In this work, based on a GaAs substrate, a self-assembly InAs quantum dot (QD) based p-i-n heterostructure is applied for fabricating electroabsorption modulator. The quantum dot electroabsorption modulation is fabricated by wet-etching technique, where the active region is formed by undercut wet-etching technique using selective etching solution (citric acid). In the device characterization, electro luminescence (EL) is first used to examine the optical transition of QD, showing 1280-1320 nm for ground state and 1220-1240 nm for the excite state. Using the photocurrent spectrum measurement, the red shift of 20 nm in photocurrent peaks from 0 V to 7 V is observed. Also, the peaks exhibit a quadratic relation against with bias, confirming QCSE effect of Q.D.. In the optical transmission measurement, 1300 nm light excites on a 300 £gm long device, obtaining 5 dB extinction by voltage swing of 7 V. By comparing with quantum well (QW) structure, the modulation efficient is in the same order of magnitude. However, the active region of QD volume is at least two orders less than QW, indicating strong QCSE can be obtained from QD and QD can have potential for high-efficient modulation. High-speed EO response with -3 dB bandwidth of 3.34 GHz is also obtained, where the main speed limitation is on the electrical isolation on the n-type GaAs substrate. Through optimizing Q.D. structure and also parasitic capacitance, Q.D. EAM can have a great potential for the application of high-speed optical modulation in optoelectronic fields.

The contactless electroreflectance¡]CER¡^ spectra of ZnO bulk has been measured at 300K. It was observed the difference between the CER spectra by using the polarization E of probe light perpendicular ( E¡æc) and parallel ( E¡üc) to the c-axis of the m-plane ZnO. In addition, a mercury lamp was focused on the sample to reduce its strength of electric field. It was observed that the CER spectrum was blue-shifted with Hg lamp being on. Hence, the observed features were attributed to excitonic transitions. The experimental spectra were fitted by Lorentzian lineshapes. The energies of the A ( B¡^, B¡]A¡^, and C excitonic transitions were determined as 3.329eV, 3.343eV and 3.387eV, respectively.

New improved model was developed to calculate the absorption and refractive-index spectra in the band-edge region for all the important compound semiconductors. An accurate absorption model including Coulomb interaction and Urbach-broadened band edge has been demonstrated for direct bandgap semiconductors. We have developed a accurate model in which a piecewise linear approximation is used for the shape of the absorption spectrum. We also propose a steep-edged compound Lorentzian line-shape function (SCL-LSF) for modeling the Urbach tail, and the line broadening of exciton absorptions. The results of applying this fitting procedure to the absorption spectra of GaAs, InP and InAs are presented, and a consistent set of band parameters are extracted. The analytical absorption model is suitable for a complete closed-form Kramers-Kronig transform of the absorption spectrum to obtain the refractive index spectrum. A band-to-band Coulomb interaction model for the refractive index spectra is presented of AlxGa1-xAs for 0 < x < 0.412, and In0.53Ga0.47As ternary semiconductors at photon energies near and above the band gap. An accurate absorption model is used to calculate the contribution on the refractive index near band-edge region through a complete closed-form Kramers-Kronig transform. By including a single oscillator Sellmeier model for the high-energy absorption spectrum, closed-form expressions are obtained for the band-edge region refractive index. Both spectra are fully described in terms of a finite set of parameters that can be interpolated for all the important compound semiconductors. The refractive index spectra are extended beyond the band-gap energy and are in excellent agreement with the available experimental data. Our new model makes accurate modeling possible for devices such as electroabsorption and electrorefraction modulators.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 242-256).

No description available.

This thesis consists of two completely separate parts: In part I some problems related to phonons in amorphous solids are considered, whilst Part II is devoted to the study of excitons in Cuprous Oxide (Cu₂O). Part I.- A theoretical model, suitable to treat vibrations in tetrahedrally coordinated amorphous systems is developed and permits the study of a number of situations of current interest. Three of these situations are studied in detail: 1) The local response of hydrogen in amorphous silicon when a single silicon is attached to one, two or three hydrogens. The differences between these three configurations are discussed and a direct connection with experimental results is suggested. 2) The interesting case of an amorphous alloy, where both, topological and substitutional disorder are present. This is treated within the spirit of the Coherent Potential Approximation. The particular alloy chosen (Si-Ge) is readily tractable because oithe similar bond characteristics of both components, which allows the neglect of force constant changes. 3) The Raman spectrum of AX₂, glasses. The model adopted permits the investigation of the local response at the defect sites for a number of defects. In order to explain the defect lines observed in the experiments, four plausible defect configurations are considered: a missing A-X bond, a X-A double bond, an A-A bond, and a square ring (two tetrahedra sharing an edge). A simple model to calculate the Raman response in amorphous solids is also outlined. Part II.- The valence band of Cu₂0 is studied in detail to account for the deviations from the hydrogenic law of the exciton spectrum. The appearance of the two series of excitons is explained in terms of a spin-orbit splitting of the valence band in the centre of the Brillouin Zone, using a Tight-Binding Approximation. The deviations of the lowest exciton levels from their expected values are seen to arise from an admixture of the two components of the split -off valence band due to direct Coulomb and exchange interactions. The Hamiltonian used corresponds to the so called "Spherical Approximation" and the results obtained are in remarkable agreement with the experiments.

Typescript (photocopy) / 164 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1982

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 98-106).

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. 119-144). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, June 2000. / Includes bibliographical references. Also available on the Internet.