Hole Injection and Rectifying Heterojunction Photodiodes through Vacancy Engineering in MoS2

The lack of techniques for counter doping in two dimensional (2D) semiconductors has hindered the development of p/n junctions, which are the basic building blocks of electronic devices. In this work, low‐energy argon ions are used to create sulfur vacancies and are subsequently “filled” with oxygen to create p‐doped MoS_2−xO_x. The incorporation of oxygen into the MoS₂ lattice and hence band‐structure modification reveal the nature of the p‐type doping. These changes are validated by X‐ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Raman spectroscopy, and photoluminescence measurements combined with density functional theory calculations. Electrical measurements reveal a complete flip in carrier polarity from n‐type to p‐type, which is further examined using temperature‐dependent transport measurements. The enhancement of p‐field‐effect transistor characteristics is facilitated by employing top‐gated transistors and area‐selective vacancy engineering only in the contact regions. Finally, on the same flake, an in‐plane MoS₂ (n)/MoS_2−xO_x (p) type‐I (straddling) heterojunction with rectifying behavior and excellent broadband photoresponse is demonstrated and explained using band diagrams. The spatial/metallurgical abruptness (<100 nm) of the heterojunctions is ascertained using Raman mapping. This process of vacancy engineering, which enables air‐stable, area‐selective, controlled, CMOS‐compatible doping of 2D semiconductors is envisioned to open new vistas in the development of high‐performance electronic and optoelectronic devices.