Electronic and optical properties of disordered getchellite: A photoreflectance, optical absorption, photoemission, and theoretical investigation

In this work, the optoelectronic properties of the getchellite crystal, a layered semiconducting disordered alloy with the chemical formula AsSbS3, are probed by a combination of complementary spectroscopic techniques, i.e., x-ray photoelectron spectroscopy together with a photoreflectance and a transmission spectroscopy. The experimental results are supported by a calculation based on density functional theory (DFT). The sample is an intrinsically p-type semiconductor whose optical properties are dominated by a direct transition. The energy of this transition is highly decreasing, by 0.22 eV, when the sample temperature increases from 20 to 300 K. A calculated band structure together with the transmission results reveals that of about 50 meV below the direct optical transition, an indirect one occurs associated with the fundamental bandgap of AsSbS3. Finally, the change in the fundamental bandgap character from indirect to direct during the reduction in material thickness from bulk to monolayer is demonstrated by the DFT calculations.