Excitons in two-dimensional semiconductors and van der Waals heterostructures

Complex quasi-particles formed by bound electron-hole pairs in semiconductors, also known as excitons, play a fundamental role in their light absorption and emission processes. Recent advances in fabrication and exfoliation techniques enabled the systematic production of few layers two-dimensional (2D) semiconductors, such as transition metal dichalcogenides and black phosphorus, where exciton binding energies are remarkably strong, which results not only in clear excitonic features in absorption and photoluminescence spectra, but also in robust excitons that are controllable e.g. by external electric and magnetic fields. Here, we provide an overview of the recent developments in opto-electronics of 2D semiconductors and discuss them in light of the current theoretical models for excitons.