High-density plasma dynamics in semiconductors.

Abstract

This dissertation presents a study of high density plasma dynamics in semiconductors. Chapter 1 serves as an introduction and presents the basics of how we will use optical nonlinearities in the study of a high density plasma. Chapter 2 develops the necessary femtosecond laser system and techniques utilized in this investigation. The basics of our colliding pulse modelocked femtosecond laser system are presented. A variety of data acquisition systems are also outlined and discussed. A detailed description of our method of chirp measurement and correction rounds out the chapter. Chapter 3 presents a study of plasma dynamics in type I and type II GaAs multiple quantum well samples. First, the samples are compared in the quasi-equilibrium regime. The transfer of carriers from the wells to the barriers in the type II sample is found to profoundly affect the optical nonlinearities. A many-body theory calculation of these nonlinearities is then presented. We also utilize the unique properties of the type II structure to study the picosecond dynamics of a one component (hole) plasma. Finally, the possibility of transient gain in the type II structure is explored and discussed. Chapter 4 describes an investigation into the gain dynamics in an optically inverted semiconductor. Spectral hole burning is observed throughout the gain region, and the dynamics of the hole burning are shown. Since this system is highly inhomogeneously broadened, these results are first modeled by a group of noninteracting, inhomogeneously broadened, two level transitions. This model permits simple insight into the dynamics, but does not do a complete job of modeling the results. So, a full many-body treatment is included to more completely describe the experiment. Chapter 5 presents a study of the dephasing time through the gain region and into the absorption region of an optically excited GaAs multiple quantum well sample. Both spectral and temporal methods for measuring the dephasing time are utilized. A distinct maximum of the dephasing time is observed at the transparency point. A many-body theory calculating the carrier-carrier scattering rate is presented to explain this maximum.