| Abstract Scope |
B-Ga2O3 demonstrates insulating properties with Mg, Fe, and Zn doping. Here we investigate Cu doping (0.25 at.%) in bulk Czochralski (CZ) and vertical gradient freeze (VGF) B-Ga2O3, with significant Cu incorporation, even with expected Cu evaporation. Representative crystals were assessed for orientation, purity, and electrical properties. The solubility and electronic behavior of Cu dopants are consistent with measured concentrations 1×1018 - 1×1019 atoms/cm3 and electrical measurements show resistivity 109-1010 Ω∙cm, with no p-type conduction. Segregation and precipitation of Cu species in the VGF material were studied with Raman spectroscopy, photoluminescence microscopy, and energy-dispersive X-ray spectroscopy. With sufficient Cu concentration, B-Ga2O3 crystals excited with ultraviolet (UV) light photodarken rapidly and exhibit decreased resistivity. This darkened state remains at room temperature for several days before decaying. The origin of photodarkening was studied with infrared spectroscopy and shown to be related to the appearance of hydrogen-containing vibrations which were not present before darkening. |