Semiconductor optical amplifier and heterojunction bipolar transistor modeling

This thesis addresses topics relevant to current research in the area of III-V semiconductor devices through theoretical and experimental contributions. Specifically, the work includes five chapters: numerical simulation and design of novel semiconductor quantum well optical amplifiers, fabrication of semiconductor waveguide grating structures with electron beam lithography, simulation and design of GaN based heterojunction bipolar transistors, a discussion of the symmetry properties of wurtzite III-N materials, and the summary.; In the first chapter I show that polarization insensitive optical gain over a wide bandwidth can be realized in coupled pseudomorphic multiple quantum well structures. I also present calculated results for 1.3 mum semiconductor optical amplifier structures based on bands calculated in the framework of an eight-band k · p model. In the second chapter I describe how the semiconductor grating structures are fabricated and 1 discuss the calculation of the reflectivity of the grating structure with coupled mode theory. In the third chapter the potential of III-Nitride materials for the fabrication of bipolar transistors is investigated theoretically. Spontaneous and piezoelectric polarization charges are utilized to create large sheet carrier densities in the base layer, thus minimizing the base spreading resistance. A hybrid model is employed to study the current gain. In the fourth chapter the transformation relationships between local pseudopotential wavefunctions for different wavevectors that are related by a symmetry transformation of the point group C6V are derived. The exploitation of these symmetry transformations implies large savings in computation time and memory in transport calculations for wurtzite structure materials. In the fifth chapter the research work is summarized.