Enhanced photoresponsivity and photodetectivity by Sb doping into Bi ₂ Se ₃ thin films for visible light photodetectors

Doping in transition metal chalcogenides (TMCs) has emerged as a prominent method for tuning various properties for potential optoelectronics applications. The prime focus of the current study is the enhancement of photodetectivity and photoresponsivity through Sb doping into Bi₂Se₃ films under heat treatment. The Sb/Bi₂Se₃ heterostructure film formation was investigated through cross-sectional FESEM (Field Emission Scanning Electron Microscopy), which also showed the intermixing of the two layers upon annealing. The enhanced crystallinity, as probed using X-ray diffraction (XRD), modified the microstructure (probed by Raman spectroscopy) and surface morphology (observed from the FESEM image). The developed phases from XRD data were identified through HRTEM and SAED patterns. The presence of the elements in the film before and after annealing was verified through EDS data. The optical changes in the films were detected by UV-visible spectroscopy. The reduction in transmittance resulted in increased absorbance and decreased optical gap. The energy gap was reduced from 1.419 (heterostructure) to 1.065 eV (mixed layer) by heat treatment, which caused a 3.043 to 3.313 increment in the refractive index. There was a two-fold enhancement in nonlinear parameters in terms of the nonlinear refractive index and third-order nonlinearity upon annealing. The increased contact angle value upon annealing signifies the enhanced hydrophobicity in the annealed films. The photoresponse efficiency increased from 5.82 × 10^-7AW^-1 (as-prepared) to 6.7 × 10^-1 AW^-1, and the detectivity increased from 1.31 × 10⁷ Jones (as-prepared) to 1.04 × 10⁹ Jones with annealing at 250 °C. The nA to mA transition in photocurrent upon annealing at 250 °C increased the photoconductivity. The resulting experimental data indicate the potential of such types of films for application in advanced visible light photodetectors and future optoelectronic devices with high energy efficiency and sensitivity.