Shortwave-infrared photoluminescence from Ge1−xSnx thin films on silicon

Ge1−xSnx thin films with Sn composition up to 7% were epitaxially grown by chemical vapor deposition on silicon. Temperature-dependent photoluminescence was investigated and the peaks corresponding to the direct and indirect transitions were observed in a wavelength range from 1.6 to 2.2 μm. The exact peak positions obtained from Gaussian fitting were fitted with an empirical temperature dependent band-gap equation (Varshni relationship). The separation between direct and indirect peaks was equal to 0.012 eV for GeSn thin film with 7% Sn content at room temperature. This observation indicates that the indirect-to-direct crossover would take place at slightly higher Sn compositions.