Engineering Ultrafast Photoconductive Response in Two-Dimensional SnS2 Through Metal Intercalation

Two-dimensional (2D) SnS2 is a layered semiconductor with a band gap in the visible range of spectrum (~ 2.3 eV) and good environmental stability.1 In an earlier study, we reported on transient photoconductivity dynamics in SnS2 following above-gap, 400 nm excitation. We found that photoexcited free carriers have high mobility of 250 ± 10 cm2 V-1 s-1 and the lifetime in the hundreds of picoseconds.2 Here, we demonstrate zero-valent intercalation of various atomic metals into the van der Waals gap of SnS2 can be used to change the lifetimes of optically excited charge carriers. Zerovalent intercalation introduces atomic metals into the van der Waals gap of 2D materials without radically altering the structure or the oxidation state of the host lattice. 3-5 It has been shown to reduce the lifetime and improve the mobility in GeS under near-gap excitation.6<br/>In the case of SnS2, we identify two metals, Cu and Cr, that increase the carrier lifetime. In fact, while all photoexcited carriers become trapped or decay within the first few hundred ps in pure SnS2, SnS2-Cr retains ~ 10% of carriers, and SnS2-Cu ~ 5% of carriers by 0.5 ns mark. At the same time, Fe and Bi intercalation shortens the carrier lifetime. Metal intercalation can thus be used to engineer the properties of SnS2 for its applications in solar energy conversion, where a longer lifetime is beneficial, to high-speed photodetectors, where minimizing the response time is important.