A SYSTEMATIC STUDY OF THE OPTICAL AND ELECTRICAL PROPERTIES OF Ge1-ySny AND Ge1-x-ySixSny SEMICONDUCTOR ALLOYS DISSERTATION

Silicon is very well known for its electronic device applications, but Si-based microelectronics will eventually reach their ultimate physical size and technological limits. In order to overcome these limitations and to broaden the role of Si technology into the realm of optical signal generation and processing, an intensive research effort has been made. As a result, a significant breakthrough has recently been achieved in fabricating Siand Ge-based direct bandgap semiconducting materials such as Ge1-ySny and Ge1-x-ySixSny alloys. These materials represent a new paradigm in the integration of optical components with Si electronics on a single chip. Therefore, in order to fully utilize these materials in potential new novel optoelectronic devices, the optical and electrical properties of the Ge1-ySny and Ge1-x-ySixSny alloys were investigated as a function of alloy composition and sample temperature. Temperature (T)-dependent photoluminescence (PL) has been investigated for p-Ge, n-Ge1-ySny (0.3% Sn), and p-Ge1-ySny (1.0% Sn) epitaxial layers grown on Si substrates. All these samples show both direct (ED) and indirect (EID) bandgap related optical PL transitions at low temperatures (LTs) and/or at room temperature (RT), but they show vastly different temperature-dependent behavior. Moreover, they all clearly show the competitiveness between the direct (ED) and indirect (EID) bandgap related PL transitions as temperature changes. In addition, PL was measured at RT for a set of n-Ge1-ySny samples with Sn contents ranging from 0.3% to 3.6%. A reduction in the PL peak energy with increasing Sn content was observed and compared with theory. Furthermore, all the measured ED PL peak energies were consistently lower than the theoretically calculated values, which