Tuning carrier density and phase transitions in oxide semiconductors using focused ion beams

We demonstrate spatial modification of the optical properties of thin-film metal oxides, zinc oxide (ZnO) and vanadium dioxide (VO₂) as representatives, using a commercial focused ion beam (FIB) system. Using a Ga⁺ FIB and thermal annealing, we demonstrated variable doping of a wide-bandgap semiconductor, ZnO, achieving carrier concentrations from 10¹⁸ cm^-3 to 10²⁰ cm^-3. Using the same FIB without subsequent thermal annealing, we defect-engineered a correlated semiconductor, VO₂, locally modifying its insulator-to-metal transition (IMT) temperature by up to ∼25 °C. Such area-selective modification of metal oxides by direct writing using a FIB provides a simple, mask-less route to the fabrication of optical structures, especially when multiple or continuous levels of doping or defect density are required.