Cu2O single crystal growth using CuCl flux and bandgap evaluation

High-quality Cu2O single crystals were grown in CuCl flux, utilizing an Al2O3 or MgO crucible and a slow-cooling technique. The resultant crystals exhibited a well-faceted cubic morphology, each with dimensions in the order of a few micrometers. The bandgap of Cu2O was evaluated by diffuse reflectance spectroscopy and photoluminescence measurement using single crystals. The measured bandgap (Eg ≒ 1.95 eV) was marginally lower than the widely reported value. However, this measured value could be reasonably asserted to be representative of the intrinsic bandgap because the single crystals experienced minimal strain from the substrate, and the optical absorbance data displayed no arbitrariness.