Low On-Resistance\nand High Carrier Mobility in β‑Ga<sub>2</sub>O<sub>3</sub> Single-Crystal Substrates through Tantalum Doping

Doping and electron\nmobility play crucial roles in determining\nthe conductivity of β-Ga<sub>2</sub>O<sub>3</sub> single-crystal\nsubstrates. This work proposes tantalum (Ta) as an effective n-type\ndopant, presenting it as an alternative to the more conventionally\nused tin (Sn) in β-Ga<sub>2</sub>O<sub>3</sub> substrates. Single\ncrystals of β-Ga<sub>2</sub>O<sub>3</sub> doped with 0.05 mol\n% Sn and Ta are grown using the optical floating zone technique. Structural\nand optical analyses revealed superior crystal quality for Ta-doped\nβ-Ga<sub>2</sub>O<sub>3</sub> grown compared to Sn-doped crystals\nin the studied materials. Both types of doped crystals exhibit a high\noptical transparency and a band gap close to 4.7 eV. With the same\namount of source material in the melt, Raman analysis shows a higher\nincorporation of Ta atoms into the β-Ga<sub>2</sub>O<sub>3</sub> lattice than that of Sn, a finding further validated by inductively\ncoupled plasma optical emission spectroscopy (ICP-OES) analysis. A\nHall mobility of 138 cm<sup>2</sup>/(V s) is determined for Ta-doped\nβ-Ga<sub>2</sub>O<sub>3</sub> substrates at a carrier concentration\nof 7 × 10<sup>17</sup> cm<sup>–3</sup>, which is one of\nthe highest reported values for melt-grown β-Ga<sub>2</sub>O<sub>3</sub> substrates. Vertical Schottky barrier diodes on Ta-doped\nsubstrates exhibit a low specific on-resistance of 0.46 ± 0.03\nmΩ-cm<sup>2</sup>, consistent with enhanced substrate conductivity.