Internal Interfaces in Exfoliated MoS₂ Exhibit Junction-like Behavior

Mechanical exfoliation remains a ubiquitous method for material deposition in van der Waals layered semiconductors, despite usually producing terraced structures where the layer count changes across the flake, resulting in variations in the band gap magnitude across the device. While most published studies circumvent this phenomenon using sophisticated fabrication processes, these internal interfaces present a unique opportunity for the realization of engineered quantum building blocks within single-crystalline materials. The electronic structure of internal interfaces in MoS₂, termed here "quasi-heterojunctions", is studied using a combination of photoluminescence and Raman spectroscopies, Kelvin probe force microscopy, and macroscopic transport measurements. In the transition between 5 to 2 to 1 layers within a single crystal, heterojunctions form, with band offsets of 22 and 24 meV in the conduction bands of the respective junctions. Variations of bandgap and electron affinity, as well as the formation of line defects, are shown to be the primary cause determining the rectification properties of the two junctions in series. Moreover, the formation of a line defect results in a space-charge region that introduces nonlinear properties to its response (I-V) curves. Finally, computational reconstruction of the measured surface potential using a finite element Poisson solver enables the determination of detailed electronic structures of the constituent segments and their quasi-heterojunctions.