Observation of impurity band conduction and variable range hopping in heavily doped (010) β-Ga2O3
Temperature-dependent resistivity and Hall measurements were performed on a heavily Sn-doped (010) β-Ga2O3 substrate grown by edge-defined film-fed method. At room temperature, the Hall electron mobility was 77.7 cm2 V−1 s−1. A maximum mobility of 95.2 cm2 V−1 s−1 was achieved at T = 185 K. Because the doping concentration is near the Mott critical value of 2.48 × 1018 cm−3, Hall electron concentration and mobility data were analyzed using the two-band model, which considers transport through both the conduction band and an impurity band. At T > 200 K, charge transport is limited by free carriers in the conduction band. The donor ionization energy was extracted to be E CD = 4 meV. At T ≤ 200 K, the net conductivity is due to electrons in the impurity band, with a concentration 7.6 × 1018 cm−3 and a low mobility of ~0.09–2.27 cm2 V−1 s−1. Over a very wide temperature range, 1.7–200 K, transport in the impurity band was found to occur via variable range hopping, where the average hopping length increases with decreasing temperature.