Photoresponse of Natural van der Waals Heterostructures

Van der Waals heterostructures consisting of two-dimensional materials offer a platform to obtain materials by design and are very attractive owing to unique electronic states. Research on 2D van der Waals heterostructures (vdWH) has so far been focused on fabricating individually stacked atomically thin unary or binary crystals. Such systems include graphene, hexagonal boron nitride, and members of the transition metal dichalcogenide family. Here we present our experimental study of the optoelectronic properties of a naturally occurring vdWH, known as franckeite, which is a complex layered crystal composed of lead, tin, antimony, iron, and sulfur. We present here that thin film franckeite (60 nm u003c d u003c 100 nm) behaves as a narrow band gap semiconductor demonstrating a wide-band photoresponse. We have observed the band-edge transition at ∼1500 nm (∼830 meV) and high external quantum efficiency (EQE ≈ 3%) at room temperature. Laser-power-resolved and temperature-resolved photocurrent measurements reveal tha...