Investigating the temperature-dependent Raman spectroscopy of Se/Bi2Te3 thin films and its enhanced photoresponse for optoelectronic applications

Abstract

The 2D Bi2Te3 narrow bandgap semiconductor is an outstanding applicant for optoelectronics and thermoelectric devices. The doping of Se into Bi2Te3 makes metal-double chalcogenide more important. In the current investigation, the Se diffusion into the Bi2Te3 film by thermal annealing at different temperatures is probed through a temperature-dependent Raman study along with other characterizations. Upon annealing, the Se/Bi2Te3 films of ∼810 nm thickness resulted in significant changes to their structural, electronic, and optical behavior. The existence of a rhombohedral Bi2Te3 phase was confirmed by structural investigation. The improvement in crystallinity and decrease in lattice strain modified the optical behavior of the films. The morphology analysis showed a slight aggregation at the higher annealed stage. The uniform and homogeneous dispersal and the composition of elements in the film were verified through surface mapping and compositional analysis. The optical investigation revealed a drop in absorbance with increased transmittance. The direct optical bandgap increased from 0.53 ± 0.002 to 0.77 ± 0.002 eV, showing a blue shift. The non-linear refractive index decreased from 3.72 to 1.85 × 10−16 m2/W upon annealing. The temperature-dependent Raman analysis demonstrated a thermally induced significant vibrational change in the material with specific additional peaks at higher annealing. Such findings can be employed as a phase change material at very high temperatures. The obtained findings are very useful for optoelectronic applications. Surface wettability shows a reduction in hydrophilicity, thus inching toward a hydrophobic one with an increase in annealing temperatures. The enhancement in the photocurrent with the increment in the annealing temperature is more suitable for photovoltaic applications.