Date of Award
Doctor of Philosophy (PhD)
Tritt , Terry
Manson , Richard
Alexov , Emil
In this work we discuss two different manifestations of electronic transport phenomena in semiconductor superlattices.
In the first problem, we analyze recent experimental data of measurements of the Seebeck coefficient in InAlAs superlattices doped with ErAs nano-particles. Inspired by the known fact that a Schottky barrier develops at the ErAs-semiconductor interface, we formulate a phenomenological transport theory that explicitly considers the energy-dependent scattering on this barrier and determine its consequences on the transport properties. We show that in the miniband conduction regime, nano-particles can realize a filtering effect by increasing the scattering rates of the slow-moving carriers leading to an increased value of the Seebeck coefficient. The magnitude of the increment depends linearly on the Schottky barrier height and saturates for large values. Our results reproduce the approximately 20 % increase in the value of the Seebeck coefficient observed experimentally. This model offers a physical, intuitive way for explaining the observed experimental behavior and allows a realistic quantitative estimate at the same time.
In the second problem, the self-consistent density response of an electron system is studied in a two-dimensional (2D) lateral superlattice with spin orbit interaction (SOI). Under the effect of the lateral periodic potential, the single-electron 2D states are broadened into minibands that are spin-split by SOI. In the case of a single fully-occupied miniband, we calculate the long wavelength limit of the polarization function for intra-band transitions, within the random phase approximation at T=0K, and identify the plasmonic dispersion relation in the effective mass approximation. The interplay between band effects and SOI coupling, considered here to be linear in the electron momentum (Rashba), is shown to generate a highly anisotropic collective excitation spectrum. If the plasmon propagating perpendicular on the superlattice axis has the characteristic frequency of the quasi one-dimensional system weakly modified by the SOI split, the one propagating along the SL axis is enhanced by the SOI that couples, through its dependence on the periodic momentum of a Bloch electron, density fluctuations in different layers of the superlattice. The excitation frequency of this mode is found to depend on the miniband width and the amplitude of the SOI coupling constant. This is the only instance we are aware of where the SOI interaction acts as an amplifier of the plasmonic modes.
Lung, Florin, "Transport Phenomena In Semiconductor Superlattices" (2011). All Dissertations. 697.