n-type dopants in (001)β-Ga2O3grown on (001)β-Ga2O3substrates by plasma-assisted molecular beam epitaxy

Ge and Sn as n-type dopants in (001) β-Ga2O3 films were investigated using plasma-assisted molecular beam epitaxy. The Ge concentration showed a strong dependence on the growth temperature, whereas the Sn concentration remains independent of the growth temperature. The maximum growth temperature at which a wide range of Ge concentrations (from 1017 to 1020 cm−3) could be achieved was 675 °C while the same range of Sn concentration could be achieved at growth temperature of 750 °C. Atomic force microscopy results revealed that higher growth temperature shows better surface morphology. Therefore, our study reveals a tradeoff between higher Ge doping concentration and high quality surface morphology on (001) β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy. The Ge doped films had an electron mobility of 26.3 cm2 V−1 s−1 at the electron concentration of 6.7 × 1017 cm−3 whereas the Sn doped films had an electron mobility of 25.3 cm2 V−1 s−1 at the electron concentration of 1.1 × 1018 cm−3.