Charge carrier mobilities and dynamics in thin film compound semiconductor materials from transient Thz absorption

Abstract

We use optical pump Thz probe spectroscopy to access the microscopic mobilities and fast charge carrier dynamics processes in polycrystalline chalcopyrite and kesterite thin films grown by coevaporation. In order to avoid complicating effects from the presence of Ga-gradients, ternary CuInSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> samples were used as a model system. Significantly different DC mobilities were found for stoichiometric and Cu-poor samples, respectively. While the stoichiometric samples exhibit Drude-like free carrier mobilities with DC mobilities up to 1200cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs at room temperature, the Cu-poor samples show non-Drude behavior, with much lower DC mobilities, indicative of carrier localization. Kesterite materials are found to show even stronger signatures of carrier localization than the chalcopyrites.