by Yip Kam-wa. / Parallel title in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1991. / Bibliography: leaf 64. / List of Figures --- p.iii / Acknowledgement --- p.vi / Abstract --- p.vii / Chapter 1. --- Introduction --- p.1 / Chapter 2. --- Effective-mass Approximation for Lattice-matched Heterostructures --- p.4 / Chapter 2.1 --- Introduction --- p.4 / Chapter 2.2 --- Formulation --- p.5 / Chapter 2.3 --- Model --- p.10 / Chapter 2.4 --- Exact Solution and Effective-mass Approximation for the Reflection Coefficient of 1-D Heterojunction --- p.15 / Chapter 2.5 --- Comparison --- p.20 / Chapter 2.6 --- Kinetic Energy Operator Ordering --- p.26 / Chapter 2.7 --- Conclusion --- p.30 / Chapter 3. --- Effective Hamiltonian for Semiconductor Heterostructures in a Uniform Magnetic Field --- p.33 / Chapter 3.1 --- Introduction --- p.33 / Chapter 3.2 --- Bloch Electron in a Uniform Magnetic Field --- p.34 / Chapter 3.3 --- Effective Hamiltonian for Heterostructures in a Uniform Magnetic Field --- p.40 / Chapter 3.4 --- Conclusion --- p.42 / Chapter 4. --- Effective-mass Approximation for a 1-D Strained Heterostructure --- p.43 / Chapter 4.1 --- Introduction --- p.43 / Chapter 4.2 --- Formulation --- p.44 / Chapter 4.3 --- Model --- p.50 / Chapter 4.4 --- Comparison --- p.54 / Chapter 4.5 --- Conclusion --- p.62 / Chapter 5. --- Conclusion --- p.63 / References --- p.64 / Appendix A --- p.65 / Appendix B --- p.67 / Appendix C --- p.68

An elliptical coordinate transformation was chosen to produce an elliptical cylindrical quantum cloak. Since an ellipse can become to a circle geometrically, research on elliptical quantum cloak provides another way to test the feasibility of the quantum cloak. In this study, it was shown that the effective mass of an elliptical cylindrical quantum cloak is simpler than an circular cylindrical one. Hence, an elliptical quantum cloak is easier to achieve experimentally.

The aim of this work was to develop an envelope function method to calculate the electronic states and optical properties of complex quantum well heterostructures, and to demonstrate its effectiveness by application to some device structures of topical interest. In particular, structures have been considered which might form the basis of intensity modulators and polarization insensitive amplifier devices for light at a wavelength of 1.55 µm. The modulator structures considered all have the general form of two coupled quantum wells of different widths as the active region. The application of an electric field in the growth direction is intended to result in a shift in the energy and spatial localisation of the confined states and produce an increase in the absorption coefficient at longer wavelengths than the zero field absorption edge. The effectiveness of certain structures is examined in terms of field induced absorption increase at 1.55 µm. A system which shows a significant increase in absorption coefficient at this wavelength on application of a practical electric field has been identified as a possible candidate for an intensity modulator. In the case of the amplifier, the active region of the most promising structure considered consists of a stepped well which comprises two layers, one with tensile and one with compressive strain. It is known that the presence of the two oppositely strained layers can result in the TE and TM gain peaks appearing at similar photon energies. Our calculations show that a suitable choice of strain and layer widths can result in a small or zero difference between the TE and TM gains at 1.55 µm, which can be important for the polarization insensitive operation of devices in optical communications applications. In order to predict the optical properties of quantum well devices it is necessary to calculate the electron and hole states for a range of in-plane wavevectors. The calculations developed and carried out in this work are based on a multi-layer (eight band) k.p model including strain effects. The interfacial boundary conditions which result from approximations to Burt's exact envelope function theory are included in the model. The effect of an electric field is modelled by including a potential energy term in each layer Hamiltonian which is equal to the average energy shift across the layer in question due to the presence of the field. The model has been developed with flexibility in mind and has applications beyond the specific devices considered in this thesis.

Presented in this thesis are extensive theoretical investigations into the causes and effects of carrier localization in InGaN/GaN quantum wells. The results of the calculations agree well with experimental data, where it is available, and provide additional insights into the mechanisms that lead to some of the experimentally observed effects of localization. Firstly, the wave functions of the electrons and holes in InGaN/GaN quantum wells have been calculated by numerical solution of the effective-mass Schrödinger equation. In our calculations we have assumed a random distribution of indium atoms, as suggested by the results of atom probe tomography: this allows us to find the contributions to the carriers' potential energy that arise from band gap fluctuations, the deformation potential and the spontaneous and piezoelectric fields. We show that the fluctuations in alloy composition can be sufficient to localize the carriers; our results are in good agreement with the results of experiment and more detailed ab-initio calculations, but we also obtain information about the distribution of localized states which those methods cannot yet provide. We find that the holes are localized on a short scale in randomly-occurring regions of high indium content, whereas the electrons are localized on a longer length scale. We consider the effect of well width fluctuations and find that these contribute to electron localization, but not to hole localization. We also simulate the low-temperature photoluminescence spectrum and find good agreement with experiment for the energy, width and shape of the photoluminescence peak. Secondly, we have used first-order time-dependent perturbation theory to study the diffusion of the carriers between their localized states at non-zero temperatures. The rates for scattering via the interaction with acoustic phonons are calculated using the carrier wave functions, and the resulting master equation for the distribution of the carriers is solved by a Monte Carlo method. We find that, even towards room temperature, the carriers are localized to a small number of states, and that their diffusion lengths are proportional to a combination of the density of localized states and the localization length. The experimentally-observed `S-shape' of the photoluminescence peak energy as a function of temperature is reproduced in our results and is explained by the thermal redistribution of holes among the localized states. A reduction of the depth of this S-shape is found as the excitation power is increased, as has been observed experimentally, and which we attribute to the saturation of the localized states.

Approved for public release, distribution is unlimited / In this thesis, SiN films grown on Si substrates were characterized using Fourier Transform Infrared (FTIR) spectroscopy. The stress in SiN films can be used to enhance of mobility of electrons and holes which increases the performance of metal-oxide-semiconductor (MOS) transistors. The samples used in this study were prepared by Applied Materials using chemical vapor deposition (CVD) technique with different growth parameters. The stress of the samples varied from 1.3 GPa compressive to 1 GPa tensile depending on the growth conditions employed. The FTIR measurement showed three distinct absorption peaks associated with Si-N, Si-H and N-H vibrational modes. The hydrogen was unintentionally incorporated into the SiN film during the CVD process due to its use as the carrier gas for the precursors. It was found from the FTIR data that the area under Si-H and N-H peaks (amount of bonds) varies in opposite directions when the film stress changes from compressive to tensile. In addition, the peak position of the Si-H absorption shifted to higher energy while the opposite was true for N-H as the stress changes from compressive to tensile. The strength and the position of the Si-N absorption peak were found to be relatively insensitive to the stress of the film. This indicates that the amount of Si-H and N-H bonds in the film is responsible for controlling the stress of the film. The use of quantum calculation of SiN molecules with different amount of Si-H and N-H bonds was used toward understanding the experimental absorption spectra. / Lieutenant, Mexican Navy

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2004. / Thesis advisor(s): Gamani Karunasiri, Ronald E. Brown. Includes bibliographical references (p. 33). Also available online.

This PhD work took place in the framework of theoretical research aimed at implementation of quantum computing schemes and algorithms in solid state devices. The electron and nuclear spins of dopant atoms implanted in silicon crystals, that already lie at the core of commercial diodes and the photovoltaic industry, are able to store quantum information longer than anything else in the solid state. Controlled manipulations of silicon qubits depend on the ability to tune the nanoscopic donor electron state: we provide a complete theoretical picture that includes, within the insightful and analytic framework of effective mass theory, the effects of the non-trivial silicon conduction band and the different lattice distortions caused by the implantation of the donor species. Calibration of the multi-valley bulk theory to account for binding energies and electron-nuclear hyperfine couplings allows improved estimates of the exchange splittings between two neighbouring donors, that provide the simplest handle for tuning two-qubit operations. Further refinements to our approach lead to exceptional agreement with experimental measurements of Stark effects, where an external electric field is used to enable local single qubit manipulations within global driving fields: we set reliable thresholds on such gating speeds across all group V donors. Finally, we propose a scalable scheme for silicon quantum computing that relies on the coherent transfer of information from Si:Bi donors, that are established as excellent memory qubits, to surface quantum dots that are easier to manipulate, within a topological surface code which enables outstanding tolerance to errors. Analysis of the optimal working regimes and inclusion of the leading sources of decoherence allow us to set out a robust design of the basic building block of future realizations.

No description available.

The heat capacity of 3He adsorbed on Grafoil (exfoilated graphite) preplated with four layers of 4He was measured between 1 and 50mK. The heat capacity was found to be linear up to 4OmK. At 3He surface densities below 4nm-2 two dimensional Fermi liquid behaviour was found and values of the hydrodynamic effective mass and Landau parameter Ff inferred. Subsequent steps in the heat capacity as a function of coverage were taken as evidence of independent 2D Fermi fluids. A low field DC SQUID pulsed NMR spectrometer was developed for future studies of magnetic order in 2D solid 3He films at ultralow temperatures

The main aim of this work was to develop a method of screening HgCdTe materials for carrier concentration and mobility using Faraday rotation θ and absorption α. Faraday rotation provides N/m*2, where N is the carrier concentration and m* is the effective mass. Since m* was not known in HgCdTe, a Faraday rotation spectrometer was developed to systematically measure it as a function of temperature and Cd mole fraction. Effective masses in n-InSb, and n-GaAs were measured and compared with known values in the literature to validate the method. Mobility is proportional to θ/α. The proportionalities were determined in HgCdTe, n-InSb, and n-GaAs at infrared wavelengths. The dissertation consists of the preface, introduction, three chapters, summary and main conclusions, references, list of publications and abstract (in Lithuanian).