Ultraviolet photodetectors (UVPDs) which play important roles in military and civil applications are normally fabricated by using wide band gap semiconductors (WBSs) as building blocks. Unfortunately, the commercialization of UVPDs based on WBSs is often limited by their relatively high fabrication cost owing to the use of very complicated growth instruments. In this work, a sensitive UVPD based on non-WBS lead sulfide (PbS) with a relatively small band gap was proposed. Device analysis revealed that the UVPD made of 48.5 nm PbS nanofilm was highly sensitive to UV illumination at 365 nm. Specifically, the responsivity and specific detectivity under 365 nm illumination were 22.25 A W–1 and 4.97 × 1012 Jones, respectively, which are comparable to or better than most of the conventional WBS-based UVPDs. The PbS nanofilm-based UVPD also exhibits excellent environmental stability. Experimental results and simulations based on technology computer-aided design software confirmed that the abnormal properties of PbS nanofilms are related to the relatively thin thickness and wavelength-dependent absorption coefficients. These results open up an opportunity for narrow band gap semiconductors to realize low-cost-sensitive UVPDs in future optoelectronic devices and systems.

In this study, a solution method derived dual-band photodetector (PD) based on silicon nanowires /PbS nanocrystalline film n-n heterojunction, which exhibits typical bias-selectable spectral response in both near-infrared (NIR) and short-wave infrared (SWIR) bands, is presented. It is found that by adjusting the polarity of the bias voltage, the photoresponse of the device can be switched between three operation modes. The device exhibits high responsivities of 2100 mA W −1 at −0.15 V and 31 mA W −1 at 0 V, respectively, in the NIR region. Remarkably, the maximum responsivity and detectivity under 2000 nm illumination are determined as 290 mA W −1 and 2.4 × 10 10 Jones, comparable to or even better than some PbS commercial PDs. The enhanced performance comes from the improved optical absorption and higher efficiency of charge separation and collection owing to the heterojunction geometry. It's also revealed that the bias-controllable spectral response is attributed to the selectively transportation of photocarriers across the junction barrier. The study demonstrates the capability of detecting two distinct IR regions with the same pixel, which has great potential in future optoelectronic systems for IR imaging applications.