Controlled Rhenium Doping of Few-Layer MoS₂ Films Grown by Metal Organic Chemical Vapor Deposition

Transition metal dichalcogenides (TMDs) are a class of layered materials that have accumulated immense interest for integration in next-generation electronic, spintronic, and photonic devices. From the initial mechanical exfoliation experiments used to isolate thin TMD flakes, a considerable about of research effort has gone into realizing industrially-adaptive, scalable synthesis methods for large-area TMD films. While vapor-phase synthesis has enabled progress in improving grain size and orientation of TMD films on a wafer-scale, the lack of scalable doping and defect control methods impedes the implementation of TMDs in many application spaces. In this work we use a completely gas-phase metal organic chemical vapor deposition (MOCVD) system to grow high quality Re-doped MoS₂ (n-type) with excellent doping control. A combination of absorbance, Raman spectroscopy, and transmission electron microscopy (TEM) will evidence controllable and uniform Re-Mo substitution over large areas. Moreover, the effect of Re introduction on MoS₂ lattice and band structure will be investigated by time-resolved photoluminescence (TRPL), scanning tunneling microscopy/spectroscopy (STM/STS), and field effect transistor (FET) characteristics. These results along with density functional theory calculations elucidate the need to reduce defect ionization energy (IE) in doped 2D systems. The high IE of Re in ML Re-MoS₂ prevents dopant activation and results in deteriorating transport properties with higher doping levels. This work will show how dopant IE can be effectively lowered by growing few-layer (FL) doped films. In addition to investigating the transport properties of doped FL films, this work will present a novel interrupted MOCVD growth scheme for precisely controlling layer number over large areas. Employing this growth scheme, the synthesis of heterostructures made with layers of differing doping percentages enabling additional functionalities.