Augmenting the broadband feature in CdS CQDs thin film photodetectors by Ag assimilation

Abstract

High-performance photodetectors (PDs) with broadband (BB) responses are crucial for many optoelectronic and imaging technologies. In the present work, BBPDs were fabricated employing simple spin coated thin films (TFs) of Cd_(1-x)Ag_xS colloidal quantum dots (CQDs), where x = 0.0 to 0.05. The x-ray diffraction (XRD) patterns of TFs confirm the formation of a cubic phase with a crystallite size very close to Bohr's atomic radius. The existence of microstructural defects like twinning/multiple twinning was confirmed by HRTEM images of the undoped and 3 wt% Ag-doped CdS QDs. The spectral tunability along with modifications in detector characteristic parameters were observed with varying concentrations of Ag. The maximum value of various performance parameters like sensitivity (S), responsivity (R), detectivity (D), and external quantum efficiency (EQE) were estimated as ∼ 1.95 × 10⁴ %, 14.67 A/W, 4.84 × 10¹² cmHz^1/2W⁻¹, and 3.8 × 10³ %, respectively. Besides, the response speed of PD was also improved by twofold due to the insertion of Ag. The fastest PD responds within 104 ms (rise time)/98 ms (fall time). The present work demonstrates BB spectral (405 nm–845 nm) detection by Cd_(1-x)Ag_xS CQDs-based PDs and tunability in the selectivity and detectable wavelength with variation of Ag dopant. The device S₃ is the fastest and demonstrated the highest S and D among all devices under 782 nm illumination; however, S₁ is optimised for PD in the present study as it delivered the best performance in the said BB spectral region with a reasonably good response speed of 200 ms.