Growth optimization and crossover of transport mechanisms in Bi₂Se₃thin films

We report the growth, structural characterization, and transport studies of Bi₂Se₃thin film on single crystalline silicon (Si), Si/SiO₂, quartz, and glass substrates by thermal evaporation method. Our results show that 300 °C is the optimum substrate temperature to obtain thec-axis (001) oriented Bi₂Se₃films 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/SiO₂substrate is selenium deficient, and the film on quartz substrate is near perfect stoichiometric providing a way to tune the electronic properties of Bi₂Se₃films through substrate selection. The film grown on quartz shows the highest mobility (2.7 × 10⁴cm²V^-1s^-1) which drops to 150 cm²V^-1s^-1for Si, 60 cm²V^-1s^-1for Si/SiO₂, and 0.9 cm²V^-1s^-1for glass substrate. Carrier concentration is n-type for Bi₂Se₃films on Si (∼10¹⁸cm^-3), quartz (∼10¹⁸cm^-3) and Si/SiO₂(∼10¹⁹cm^-3) substrate with a clear indication of frozen out effect around 50 K for Si/SiO₂and Si substrate. Longitudinal resistivity of Bi₂Se₃film on Si/SiO₂substrate 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.