Degenerate doping in β -Ga 2 O 3 single crystals through Hf-doping

Abstract n-type conductivity of β -Ga 2 O 3 grown from the melt is typically achieved using Sn and Si. In this paper, we experimentally and computationally investigate Hf doping of β -Ga 2 O 3 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 + O 2 atmosphere. We demonstrate Hf dopants, predicted to incorporate on the octahedral Ga II site as a shallow donor, achieve degenerate doping in β -Ga 2 O 3 with a measured electron concentration ∼2 × 10 19 cm −3 , mobility 80–65 cm 2 V −1 s −1 , and resistivity down to 5 mΩ cm in our samples. The concentration of Hf was measured to be 1.3 × 10 19 atoms cm −3 using glow discharge mass spectroscopy on doped samples, confirming Hf to be the cause of n-type conductivity (electron concentration ∼2 × 10 19 cm −3 ).