Vanadium doped beta-Ga2O3 single crystals: Growth, Optical and Terahertz characterization
We report the growth of electrically-resistive vanadium-doped beta-Ga2O3 single crystals via the optical floating zone technique. By carefully controlling the growth parameters V-doped crystals with very high electrical resistivity compared to the usual n-type V-doped beta-Ga2O3 (ne~10^(18)/cm^3) can be synthesized. The optical properties of such high resistive V-doped b-Ga2O3 are significantly different compared to the undoped and n-doped crystals. We study the polarization-dependent Raman spectra, polarization-dependent transmission, temperature-dependent photoluminescence in the optical wavelength range and the THz transmission properties in the 0.2 - 2.6 THz range. The V-doped insulating Ga2O3 crystals show strong birefringence with refractive index contrast Dn of 0.3+-0.02 at 1 THz, suggesting it to be an ideal material for optical applications in the THz region.