Degenerate doping in β-Ga2O3 single crystals through Hf-doping

n-type conductivity of β-Ga2O3 grown from the melt is typically achieved using Sn and Si. In this paper, we experimentally and computationally investigate Hf doping of β-Ga2O3 single crystals using UV-vis-NIR absorption and Hall effect measurements and hybrid functional calculations. Unintentionally-doped and Hf-doped samples with a nominal concentration of 0.5at% were grown from the melt using vertical gradient freeze and Czochralski method in mixed Ar + O2 atmosphere. We demonstrate Hf dopants, predicted to incorporate on the octahedral GaII site as a shallow donor, achieve degenerate doping in β-Ga2O3 with a measured electron concentration ∼2 × 1019 cm−3, mobility 80-65 cm2 V−1 s−1, and resistivity down to 5 m cm in our samples. The concentration of Hf was measured to be 1.3 × 1019 atoms cm−3 using glow discharge mass spectroscopy on doped samples, confirming Hf to be the cause of n-type conductivity (electron concentration ∼2 × 1019 cm−3).