Wide-Range Controllable n-Doping of Molybdenum Disulfide (MoS₂) through Thermal and Optical Activation

Abstract

Despite growing interest in doping two-dimensional (2D) transition metal dichalcogenides (TMDs) for future layered semiconductor devices, controllability is currently limited to only heavy doping (degenerate regime). This causes 2D materials to act as metallic layers, and an ion implantation technique with precise doping controllability is not available for these materials (e.g., MoS2, MoSe2, WS2, WSe2, graphene). Since adjustment of the electrical and optical properties of 2D materials is possible within a light (nondegenerate) doping regime, a wide-range doping capability including nondegenerate and degenerate regimes is a critical aspect of the design and fabrication of 2D TMD-based electronic and optoelectronic devices. Here, we demonstrate a wide-range controllable n-doping method on a 2D TMD material (exfoliated trilayer and bulk MoS2) with the assistance of a phosphorus silicate glass (PSG) insulating layer, which has the broadest doping range among the results reported to date (between 3.6 × 10(10) and 8.3 × 10(12) cm(-2)) and is also applicable to other 2D semiconductors. This is achieved through (1) a three-step process consisting of, first, dopant out-diffusion between 700 and 900 °C, second, thermal activation at 500 °C, and, third, optical activation above 5 μW steps and (2) weight percentage adjustment of P atoms in PSG (2 and 5 wt %). We anticipate our widely controllable n-doping method to be a starting point for the successful integration of future layered semiconductor devices.

Recent Advances in Doping of Molybdenum Disulfide: Industrial Applications and Future Prospects

“…Thermal doping is one of the most effective strategies for doping of 2D TMDs and is generally carried out by “vapor deposition or diffusion of doping materials” in a (vacuum) furnace, mostly during the growth of MoS 2 for substitutional doping or by vapor deposition on the MoS 2 surface for surface charge transfer doping. Substitutional doping during MoS 2 growth can be achieved by vapor deposition of Se and/or MoSe 2 for Se dopant, by the controlled thermal/optical annealing activation process after depositing phosphorus silicate glass (PSG) for phosphor doping and transferring MoS 2, by chemical vapor transport (CVT) approach using Br 2 , I 2, etc. as transportation agents for dopants such as Re, or Co, Fe, or Nb, or Au, by chemical vapor deposition (CVD) using chlorides such as ReCl 2 and NbCl 5 for the doping of Re and Nb, by diffusion of a ML (Mo/Nb/Mo or transition metal (Fe, Co, Ni, Cu)/Mo) for Nb and transition metals (TMs) .…”

“…Park et al presented an n‐doping process with three‐steps consisting of: i) PSG deposition (and surface dopant control by phosphor out diffusion between 500 and 900 °C) and MoS 2 transfer on PSG, ii) thermal activation at 500 °C, and iii) optical activation using a laser with wavelengths of 520, 655, and 785 nm (due to the different light‐absorption properties of MoS 2 at different wavelengths) for phosphor‐doped MoS 2 ( Figure ) . This method showed a wide‐range n‐doping concentration control and it could be a promising method for the integration of 2D semiconductor devices.…”

“…Cartoon showing three‐step (n‐type) PSG‐doping process on MoS 2 through thermal activation. Reproduced with permission . Copyright 2015, American Chemical Society.…”

Controlled Layer Thinning and p‐Type Doping of WSe2 by Vapor XeF2

“…Also, the type and height of Schottky barrier formed at the contact/TMDs interface, which determine the contact resistivity, can be tuned by doping TMDs . Although a lot of research have been conducted on the doping of MoS 2 , the study of methods for doping WSe 2 , especially with good air‐stability, scalability, and controllability, is still quite limited.…”

Rhenium-doped MoS2 films

“…[12][13][14] However, for n-type dopants, the reports are limited. 15 Theoretical work by Dolui et al 12 highlights a number of possible dopants for MoS 2 . Re substitution was identified as a good candidate for n-type doping with the lowest activation energy of all of the elements they considered.…”