Reduced carrier–phonon scattering and enhanced absorption in silver-doped transition metal dichalcogenide photodetectors

Abstract

Bulk tungsten disulfide (WS₂), a semiconductor with a bandgap of ∼1.35 eV, has low photoresponsivity owing to poor optical absorbance, which restricts its application in high-performance photodetection. The study observed that the doping of silver in WS₂ (Ag:WS₂) enhanced the photoelectronic response. Chemically, Ag was incorporated with WS₂, and powder X-ray diffraction (PXRD) confirmed the presence of Ag (in the cubic phase) and WS₂ (in the trigonal phase) in the sample. Further analysis of the structure, morphology, and purity of the material was conducted using high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM), and Raman spectroscopy. HRTEM revealed the sheet-like morphology of WS₂ and the presence of spherical Ag nanoparticles in Ag:WS₂. A threefold increase in absorbance of WS₂ upon introducing Ag was observed in absorption (UV-Vis) spectra. Lateral metal–semiconductor–metal (MSM) photodetectors were fabricated using pristine WS₂ (control) and Ag:WS₂ (test) to evaluate their photodetection capabilities. Strong phonon scattering, often induced by intrinsic vacancy defects, can significantly hinder the performance of carrier transport, resulting in poor photodetection. Comparative analysis of these devices under dark conditions and exposure to solar AM 1.5G light revealed that the Ag:WS₂ (test) device exhibited a ∼9-fold increase in photocurrent compared to its pristine WS₂ (control) counterpart under the same illuminated conditions. Further, we demonstrate a ∼6-fold increase in the carrier lifetime in silver-doped test devices using transient absorption, implying an effective reduction in carrier–phonon scattering. This study presents a cost-effective, straightforward, and in situ silver doping approach for WS₂, enabling enhanced optical absorption and improved photodetection performance.