Investigation of sub - bandgap absorption in iron pyrite : optical and electrical measurements

We investigate sub-bandgap absorption in pyrite FeS 2 single-crystals, using both natural and synthetic crystals. Both types of crystals show non-negligible magnitudes of sub-bandgap absorption. To test whether the origin of the residual sub-bandgap absorption is partially due to a lower bulk bandgap than previously thought, we conduct temperature-dependent electrical measurements on natural and synthetic crystals. Unlike previous measurements on pyrite, our electrical measurements are done in a sulfur atmosphere to avoid FeS formation. Using conductivity data in the intrinsic regime along with extrapolated Hall mobility data, the extracted bandgap is more than 0.1 eV lower than the literature value of 0.95 eV. However, higher-temperature Hall data are needed to gain a more reliable bandgap estimate. Thesis Supervisor: Tonio Buonassisi Title: Associate Professor of Mechanical Engineering