Engineering ultrafast carrier dynamics in GeS: nanostructuring and small molecule intercalation

Germanium sulfide (GeS) is a 2D semiconductor with high carrier mobility and a moderate band gap of about 1.5 eV, which holds promise for high-speed optoelectronics and photovoltaics. We use time-resolved THz spectroscopy to investigate ultrafast carrier dynamics in in GeS single crystals as well as in GeS nanoribbons. In both bulk and nanostructured GeS, we find that near gap excitation at 1.55 eV results in much longer lived photocarriers compared to 3.1 eV excitation. We also explore how intercalation of small molecules influences the photoexcited carrier dynamics in GeS. We find that presence of edge states in nanoribbons results in decreased carrier lifetime. Organic molecules such as octylamine, which do not form chemical bonds with the host GeS layers, increase photoexcited carrier lifetime. These findings demonstrate the possibility of engineering the properties of 2D materials by intercalation.