Controlling n-type conductivity of β-Ga2O3 by Nb doping

It has been confirmed that Si, Sn, and Ge are effective n-type dopants for β-Ga2O3. This letter shows that Nb doping is also a viable method for controlling the electrical resistivity and carrier density of β-Ga2O3, corresponding to the theoretical calculations about the doping of Ga2O3 with Nb [H. Peelaers and C. G. Van de Walle, Phys. Rev. B 94(19), 4 (2016)]. β-Ga2O3 single crystals with different Nb concentrations were grown by the optical floating zone method. The electrical resistivity can be varied from 3.6 × 102 Ω cm to 5.5 × 10−3 Ω cm by increasing the Nb doping concentration, and the related free carrier concentration increases from 9.55 × 1016 cm−3 to 1.8 × 1019 cm−3. The transmittance spectra and photoluminescence spectra were measured to systematically study the optical properties of Nb-doped β-Ga2O3 single crystals. The strong absorption near the IR region in the crystals is related to the increase in conductive electrons, and the decrease in blue luminescence intensity indicates a decrease in the VO concentration induced by increasing the carrier concentration.