| This dissertation addresses the application of theoretical and computational methods to examine heterostructure devices based on planar semiconductors. The thesis pursues III-V nitrides and ferroelectrics like LiNbO3 and BaxSr1-xTiO 3. GaN and other nitrides exhibit a large polarization charge arising from the built in polarization revealed in the [1000] growth direction, and are also wide band-gap materials (with the exception of InN). The nitrides are important for high-power/high-temperature electronics and for short wavelength light emitters. Our studies address important issues in large bandgap junctions, transistors and light emitters.; One of the salient results of our studies has been the first calculations of tunnel current in polar junctions and the potential of using built in polar charge at interface to design junctions. We find that novel junctions cam be designed to produce tailorable I-V characteristics. Our studies have led to experimental realization of such tailorable junctions.; We also present results on charge control in ferroelectric-nitride structures where post growth junction tailoring can be carried out (using poling) to create functional devices. This leads to a new class of devices such as switches.; We have developed extensive charge control, Monte Carlo based transport models and device simulation techniques to examine nitride based transistors. These studies allow us to examine mobility, transit time, high frequency behavior, noise, transconductance, etc.; We have examined device non-linearity issues, scaling issues, temperature dependence, noise sources, and device design optimization issues. Our results are closely coupled to experimental results. Role of unusual velocity-field relations, self-heating and non-equilibrium phonons is examined.; III-V nitride based light emitters often exhibit a very high radiative efficiency, higher than the presence of dislocations in the system suggests. Calculations indicate however, that local disorder like interface roughness, and alloy fluctuation change the nature of electron transport from Bloch-like to hopping transport. This localization protects the electrons (and holes, which are far less mobile than electrons) from getting trapped in the dislocations which exist at a larger length scale. |
