Growth optimization and crossover of transport mechanisms in Bi 2 Se 3 thin films.

We report the growth, structural characterization, and transport studies of Bi 2 Se 3 thin film on single crystalline silicon (Si), Si/SiO 2 , quartz, and glass substrates by thermal evaporation method. Our results show that 300 °C is the optimum substrate temperature to obtain the c -axis (001) oriented Bi 2 Se 3 films on all the substrates. The film grown on the Si substrate has the minimum crystalline disorder. The energy-dispersive x-ray spectroscopy results show that film on Si substrate is bismuth deficient, the film on Si/SiO 2 substrate is selenium deficient, and the film on quartz substrate is near perfect stoichiometric providing a way to tune the electronic properties of Bi 2 Se 3 films through substrate selection. The film grown on quartz shows the highest mobility (2.7 × 10 4 cm 2 V -1 s -1 ) which drops to 150 cm 2 V -1 s -1 for Si, 60 cm 2 V -1 s -1 for Si/SiO 2 , and 0.9 cm 2 V -1 s -1 for glass substrate. Carrier concentration is n-type for Bi 2 Se 3 films on Si (∼10 18 cm -3 ), quartz (∼10 18 cm -3 ) and Si/SiO 2 (∼10 19 cm -3 ) substrate with a clear indication of frozen out effect around 50 K for Si/SiO 2 and Si substrate. Longitudinal resistivity of Bi 2 Se 3 film on Si/SiO 2 substrate shows different behavior in three different temperature regions: temperature dependent resistivity region due to electron-phonon scattering, a nearly temperature independent resistivity region due to electron-phonon and electron-ion scattering, and a quantum coherent transport region.