Semiconductor heterostructures are an important building block of many of the electronic and optoelectronic devices that have been developed in the past 40 years. They are obtained by growing thin films of dissimilar semiconductors on top of each other using conventional epitaxial growth techniques. The semiconductors have different bandgaps, and thus the approach can be used to control the bandgap of the system, which is known as bandgap engineering. The emergence of twodimensional (2D) materials has expanded the possibilities of bandgap engineering beyond the constraints of traditional growth methods. In particular, vertical stacks of dissimilar 2D materials, bonded by van der Waals interactions, have been extensively explored 1, as well as in-plane lateral heterojunctions made from atomic layers with different compositions 2. A peculiar property of monolayer semiconductors, such as molybdenum …