A very low temperature (170 °C) crystallization of amorphous-Ge thin film on glass via Au induced layer exchange process in amorphous-Ge/GeOx/Au/glass stack and electrical characterization

Abstract

We report the realization of polycrystalline (poly)-Ge thin film on glass (insulator) at a significantly low temperature of ~170 °C. We realized it using Au induced layer exchange crystallization scheme in a thin film stack having amorphous (a)-Ge/GeOx/Au/glass structure. The observed crystallization temperature is one of the lowest values reported in the literature. The paper also discusses the interface energetics that drives the crystallization in detail. Au has an extremely low solubility of ~1.3 × 107 cm−3 in Ge at this low processing temperature. The layer exchange process facilitates an effective etching of the Au layer, resulting in a poly-Ge thin film free of contamination from residual Au impurities within EDS’s sensitivity. However, the poly-Ge thin film exhibits a p-type semiconducting behavior, with a moderate doping concentration of ~1.3 × 1017 cm−3, and a low resistivity ~1 Ω cm at RT due to point defects induced acceptor states. The thin film showed a mobility ~50 cm2 V−1-s−1 at RT, highest for a poly-Ge thin film formed at such low temperature. The temperature dependence of mobility indicates a high barrier of ~84 meV at the grain boundaries, which serve as the main scattering mechanism limiting the carrier conduction.