Measurements on Thermal and Electrical Properties and Characterizations on Annealed Samples

Abstract

The temperature dependences of thermal, electrical conductivity and Seebeck coefficients provide the critical information on the thermoelectric properties of the materials. The recent advancements in the converting efficiency of thermoelectrics have been attributed to the modification on material inhomogeneity of microstructures by hot pressing or simply cooling the melt to reduce the thermal conductivity. On the other hand, due to its time-consuming preparation/processing and unnecessary good crystalline quality (for thermoelectric applications), the processing of thermoelectric materials by crystal growth resulted in very few investigations. In this section, the thermoelectric properties of CdTe, grown by PVT, will be presented and compared with CdZnTe grown by directional solidification from the melt. Two different types of CdS crystals were produced from the PVT process in our laboratory, i.e., the “clear” and the “dark”, even though the growth parameters were kept essentially the same. To investigate the cause of this optical difference, the studies were emphasized on the stoichiometry changes of the crystals through the formation of point defects and their complexes. In the study, the approach was to subject the CdS crystals to heat treatments in the presence of Cd, S, and Se vapor and then compared their low-temperature photoluminescence (PL) spectra complemented with the measurements of electrical properties.