New Assembly-Free Bulk Layered Heterostructures: Electronic, Mechanical, and Optical Properties

In principle, a vast number of unique van der Waals heterostructures can be created through the vertical stacking of two-dimensional materials, resulting in unprecedented potential for material design. However, this widely employed synthetic method for generating van der Waals heterostructures is slow and imprecise. Here, we computationally study the properties of a new class of layered bulk materials, which we call assembly-free bulk layered heterostructures, wherein the individual layers are of dissimilar chemical composition. We find that these bulk materials exhibit properties similar to vertical heterostructures without the complex and unscalable stacking process. Using state-of-the-art computational approaches, we find some of these materials are potentially well suited for photovoltaic and photodetector applications as they possess visible spectrum band gaps. Additionally, we study livingstonite (Hg(SbS₂)₄), a naturally occurring mineral which exists as a bulk lattice-commensurate heterostructure. We find that both the bulk and isolated bilayers of livingstonite exist as a type-II heterojunction with infrared band gaps. This is the first report of a naturally occurring mineral with these electronic properties.