Quasi-Two-Dimensional Phenomena at Aluminum-Gallium - Arsenide - Gallium-Arsenide Heterointerfaces: Multiple Quantum Wells and Modulation-Doped Structures (Superlattice, Modfet, Semiconductors)

Abstract

This thesis describes a subset of phenomena at AlGaAs-GaAs heterointerfaces related to multiple quantum wells and modulation-doped structures. In the first section, two important results concerning multiple quantum well systems are described: optical absorption coefficients and exciton oscillator strengths in AlGaAs-GaAs multiple quantum wells are greatly enhanced as well widths become narrower: this effect is in excellent agreement with recent calculation. Additionally acceptor energies in quantum wells are studied both theoretically and experimentally. The theoretical study is extended to include the effects of magnetic, electric, and stress fields on acceptors in GaAs and in AlGaAs-GaAs quantum wells.

In the second section an improved charge control model for MODFETs is described which predicts some observed experimental phenomena. This model uses boundary conditions obtained from a numerical solution of Schrodinger's and Poisson's equations at an AlGaAs-GaAs heterointerface. Finally, the first measurements of electron velocity versus electrical field in a modulation-doped system using the geometric magnetoresistance method are reported. These results indicate that a high low-field electron mobility is not very important for MODFET operation.