n -type dopants in (001) β -Ga 2 O 3 grown on (001) β -Ga 2 O 3 substrates by plasma-assisted molecular beam epitaxy

Ge and Sn as n -type dopants in (001) β -Ga 2 O 3 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 10 17 to 10 20 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 -Ga 2 O 3 films grown by plasma-assisted molecular beam epitaxy. The Ge doped films had an electron mobility of 26.3 cm 2 V −1 s −1 at the electron concentration of 6.7 × 10 17 cm −3 whereas the Sn doped films had an electron mobility of 25.3 cm 2 V −1 s −1 at the electron concentration of 1.1 × 10 18 cm −3 .