Photoconductivity spectroscopy of epitaxial germanane devices

Germanane, a 2D sheet of hydrogen terminated germanium atoms, has recently generated a great deal of interest. Unlike graphene, which has been the focus of 2D materials for almost a decade, germanane has a direct band gap ($\sim$ 1.5 eV) and strong spin-orbit coupling. Additionally, it is predicted that changing the surface functionalization of germanane will allow tuning of the band gap, which makes it promising for electronic and opto-electronic applications. Here, we investigate wavelength dependent absorption and transport properties of optically excited carriers via photoconductivity on germanane. Samples with thicknesses ranging from several atomic layers up to 250 nm have been studied. We observe an absorption edge as a function of wavelength, as expected for a semiconducting material. There appears to be a small shift to shorter wavelengths for thinner samples. The dependence on intensity and temperature are also investigated, as well as the bias dependence. These results have implications for the use of germanane in future applications.