Tuning of Electronic and Photonic Properties of monolayer MoS2 via doping
The development of doping studies has provided an efficient route to tune and improve the properties of the 2D materials. However, the impact of the doping on the structural, electronic, and photonic properties of in situ-doped monolayers remains unanswered due to challenges including strong film substrate charge transfer, and difficulty achieving doping concentrations greater than 0.3 at%. Toward this goal, a variety of efforts have focused on tuning 2D layers by, for example, nanoparticles decoration and substrate engineering, which have significantly improved the local electronic and optoelectronic properties. However, such property engineering relies on external forces to control the 2D properties. Substitutional doping, on the other hand, is a well-established technique in the field of semiconductor epitaxy and is a proven method for controlling the semiconductor properties from within the lattice. Therefore, substitutional doping is likely the ideal method to tune the electronic and photonic properties of 2D materials.
Recently, Susan Fullerton-Shirey and their colleagues have reported in situ rhenium (Re) doping of synthetic monolayer MoS2 with ≈1 at% Re in the Journal of Advanced Functional Materials. By Raman and PL measurements, they have shown a significant electron doping in the Re-MoS2 monolayer films. X-ray photoelectron spectroscopy (XPS) and high-resolution scanning transmission electron microscopy (HRSTEM) have confirmed substitutional doping of Re in the monolayer MoS2 lattice with an estimated doping concentration of up to ≈1 at%. Current–voltage (I–V) characteristics which is measured by conductive atomic force microscopy (CAFM), reveal a transition from rectification (pristine MoS2) to Ohmic (Re-MoS2), suggesting that Re-MoS2 is degenerately doped. Furthermore, scanning tunneling microscopy/spectroscopy (STM/S) and XPS characterization have further proved a 0.5 eV Fermi level shift toward the conduction band after doping, resulting in nearly degenerate n-type doping, which agrees with density functional theory (DFT) calculations. These results have provided the foundational knowledge of how Re-doping of 2D layers impacts the electronic and photonic properties, and enables the development of a robust technique for realization of low-defect transition metal dichalcogenides (TMD)-based technologies.