Transport characteristics of novel degenerate semiconductor materials: Chalcogenide based thermoelectric systems and cadmium oxide based thin film transparent conducting oxide systems.

摘要

Extensive charge transport measurements of new thermoelectric and transparent conducting oxide degenerate semiconductor materials have been reviewed. Measurements of electrical conductivity, thermopower, carrier mobility and carrier concentration as a function of temperature for these systems have been studied to give insight into the fundamental electrical transport processes, and provide feedback for the development and improvement of materials for practical applications. This research has been multidisciplinary, requiring the collective skills of researchers in chemistry, materials science, physics and electrical engineering.; Thermoelectric materials based upon CsBi4Te6, Pb 5Bi6Se14, Yb5In2Sb 6, AgPb18BSbTe20, beta-K2Bi 8Se13 and Rb2Bi8Se13 were investigated with the goal of exceeding the performance of commercially available Bi2Te3 based alloys, the accepted standard for cooling applications at or below room temperature. Studies included modifying transport properties of these thermoelectric materials through alloying and doping, as well as small modifications of the stoichiometric ratios of the constituent elements.; Thermoelectric materials based upon CsBi4Te6 and beta-K 2Bi8Se13 appear quite promising below room temperature and in several instances have exceeded the performance of Bi2Te 3 based alloys. Thermoelectric materials based upon beta-K2Bi 8Se13, Pb5Bi6Se14, AgPb 18SbTe20 and Rb2Bi8Se13 all exhibit figure of merit values that continue to increase above room temperature. These materials appear to be promising candidates for thermoelectric applications above 400 K.; Transparent conducting oxide thin films based upon CdO grown by both MOCVD and PLD techniques were studied. The primary goal was to exceed the electrical performance of commercially available indium tin oxide, the acknowledged standard for optoelectronic applications of TCOs. This investigation resulted in improved film quality through new MOCVD precursors and modifications in growth conditions, as well as improvements in the electrical and optical properties through both doping and employing multilayer thin film structures. Improved electrical properties of both undoped and doped CdO over that of ITO were achieved without reduction in optical transparency, and increased optical transparency was achieved through the Burstein-Moss shift.