Temperature dependent Raman and photoresponse studies of Bi2Te3 thin films annealed at different temperatures for improved optoelectronic performance

Abstract

Nanocrystalline Bi₂Te₃ thin films of 800 nm thickness synthesized via a thermal evaporation method were annealed at various temperatures, which induced notable changes in both structural and optical characteristics. Structural analysis confirmed the presence of the rhombohedral Bi₂Te₃ phase in the material. The crystallinity got enhanced at increased annealing temperature. Temperature-dependent Raman studies revealed a red shift in the vibrational modes. Photoluminescence data revealed a blue shift of the emission edge, primarily attributed to the annealing-induced alteration in crystallinity, resulting in greater electron–hole emission efficiency. Morphological analysis provides insights into the slight agglomeration of the films at higher annealing temperatures. The uniform distribution of constituent elements in the films was confirmed through EDX and surface mapping. The optical study indicated a reduction in transmittance values, with increase in the absorption coefficient. The red shift of the absorption edge implied a decrease in the direct optical bandgap value from 0.528 to 0.506 eV. The estimated static refractive index and linear dielectric constant exhibited an increasing trend at higher annealing temperatures. The enhanced non-linear refractive index ranging from 3.62 × 10⁻⁹ to 3.96 × 10⁻⁹ esu resulted in the increase in non-linear susceptibility with annealing. Surface wettability studies demonstrated high hydrophilicity at increased annealing temperature. Photo-response studies indicated an increment in the photo-current for higher temperature annealed films. The observed optimized properties of the films are suitable for various optoelectronic applications, such as absorber layers for solar cells, infrared related devices, and other photo-response applications.