Tuning the photoresponsivity, sensitivity, and detectivity of Bi/Sb2S3 heterostructure films for visible-light photodetectors.

Bilayer heterostructure films are of great importance for photodetector applications, and tuning photodetector parameters by intermixing constituent layers via annealing is a prominent approach. The primary objective of this study is to enhance photoresponse and photodetection by Bi diffusion into Sb2S3 films through heat treatment. The Bi/Sb2S3 films were formed by evaporation and verified by cross-sectional FESEM, which confirmed the intermixing between layers. FESEM was used to probe the surface morphology, while XRD and Raman spectroscopy were used to investigate the changes in structural properties. HRTEM and SAED confirmed the phases identified by XRD. The elemental composition in both the annealed and as-deposited forms was verified by EDX. UV-visible spectroscopy was used to evaluate the optical parameters. The reduced transmittance and increased absorbance resulted in a decreased energy gap. The energy gap reduced to 1.764 (mixed layer) from 2.317 eV (bilayer) after heat treatment. An increase of 0.235 in the refractive index (2.611 to 2.846) was observed. The increment in the nonlinear refractive index is twofold, as seen for the third-order susceptibility. The reduced contact angle signifies an increase in hydrophilicity. Increased photosensitivity from 33% (un-annealed) to 51% (annealed) and responsivity from 4.37 × 10-5 to 4.75 × 10-3 A W-1 were observed after 250 °C annealing. The photodetectivity also increased from 9.55 × 107 to 1.06 × 109 after 250 °C annealing. The obtained results from the study will facilitate the development of advanced visible-light photodetectors and future optoelectronic devices.