Low On-Resistance and High Carrier Mobility in β-Ga₂O₃ Single-Crystal Substrates through Tantalum Doping

Doping and electron mobility play crucial roles in determining the conductivity of β-Ga2O3 single-crystal substrates. This work proposes tantalum (Ta) as an effective n-type dopant, presenting it as an alternative to the more conventionally used tin (Sn) in β-Ga2O3 substrates. Single crystals of β-Ga2O3 doped with 0.05 mol % Sn and Ta are grown using the optical floating zone technique. Structural and optical analyses revealed superior crystal quality for Ta-doped β-Ga2O3 grown compared to Sn-doped crystals in the studied materials. Both types of doped crystals exhibit a high optical transparency and a band gap close to 4.7 eV. With the same amount of source material in the melt, Raman analysis shows a higher incorporation of Ta atoms into the β-Ga2O3 lattice than that of Sn, a finding further validated by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. A Hall mobility of 138 cm2/(V s) is determined for Ta-doped β-Ga2O3 substrates at a carrier concentration of 7 × 1017 cm–3, which is one of the highest reported values for melt-grown β-Ga2O3 substrates. Vertical Schottky barrier diodes on Ta-doped substrates exhibit a low specific on-resistance of 0.46 ± 0.03 mΩ-cm2, consistent with enhanced substrate conductivity.