Unveiling the origin of n-type doping of natural MoS2: carbon (original) (raw)
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Evidence of Native Cs Impurities and Metal–Insulator Transition in MoS 2 Natural Crystals
as the presence of a bandgap allows for an effective charge commutation and hence for logic and optoelectronic operations. MoS 2 is also highly appealing for low-power and flexible electronics and, despite the relatively low mobility and still open issues on its contact resistance, the reduced short-channel effects and the alleviated band-to-band tunneling at the metal junctions make it a viable option for ultimately scaled transistors with promising perspectives for the next technological nodes in the semiconductor roadmap. On top of these technology drivers, a wide number of physical properties can also be accessed by taking benefit from the concomitant twodimensional (2D) and semiconducting character of MoS 2 . Among them is the possibility to optically tune the spin and valley index polarization of carriers aiming at the realization of so-called spin-valleytronics and the observation of a gate tunable metal-insulator transition (MIT) in monolayer and few layer MoS 2 . The latter phenomenon is associated with the strong electronic correlation occurring at the 2D level in mechanically exfoliated MoS 2 where the carrier population is n-type and can be tuned via gate bias control. Despite the highly effective charge modulation and incipient attempts to tune the doping inside MoS 2 , it is not fully clear what is the physical origin of its intrinsic doping and how to induce or manipulate it. Elucidating this aspect not only may help understanding fundamental electronic features and correlate them with the physical constitution of the MoS 2 crystals, but it can also be used to modulate doping in MoS 2 down to the 2D limit.
Reconfiguring crystal and electronic structures of MoS2 by substitutional doping
Nature communications, 2018
Doping of traditional semiconductors has enabled technological applications in modern electronics by tailoring their chemical, optical and electronic properties. However, substitutional doping in two-dimensional semiconductors is at a comparatively early stage, and the resultant effects are less explored. In this work, we report unusual effects of degenerate doping with Nb on structural, electronic and optical characteristics of MoS2 crystals. The doping readily induces a structural transformation from naturally occurring 2H stacking to 3R stacking. Electronically, a strong interaction of the Nb impurity states with the host valence bands drastically and nonlinearly modifies the electronic band structure with the valence band maximum of multilayer MoS2 at the Γ point pushed upward by hybridization with the Nb states. When thinned down to monolayers, in stark contrast, such significant nonlinear effect vanishes, instead resulting in strong and broadband photoluminescence via the form...
Carbon Incorporation in MOCVD of MoS2 Thin Films Grown from an Organosulfide Precursor
Chemistry of Materials, 2021
With the rise of two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors and their prospective use in commercial (opto)electronic applications, it has become key to develop scalable and reliable TMD synthesis methods with well monitored and controlled levels of impurities. While metal-organic chemical vapor deposition (MOCVD) has emerged as the method of choice for large-scale TMD fabrication, carbon (C) incorporation arising during MOCVD growth of TMDs has been a persistent concern-especially in instances where organic chalcogen precursors are desired as a less hazardous alternative to more toxic chalcogen hydrides. However, the underlying mechanisms of such unintentional C incorporation and the effects on film growth and properties are still elusive. Here, we report on the role of C-containing side-products of organosulfur precursor pyrolysis in MoS2 thin films grown from molybdenum hexacarbonyl Mo(CO)6 and diethyl sulfide (CH3CH2)2S (DES). By combining in situ gas-phase monitoring with ex situ microscopy and spectroscopy analyses, we systematically investigate the effect of temperature and Mo(CO)6:DES:H2 gas mixture ratios on film morphology, chemical composition, and stoichiometry. Aiming at high-quality TMD growth, that typically requires elevated growth temperatures and high DES:Mo(CO)6 precursor ratios, we observed that temperatures above DES pyrolysis onset (≳600ºC) and excessive DES flow result in the formation of nanographitic carbon, competing with MoS2 growth. We found that by introducing H2 gas to the process DES pyrolysis is significantly hindered, which reduces carbon incorporation. The C content in the MoS2 films is shown to quench the MoS2 photoluminescence and influence the trion-to-exciton ratio via charge transfer. This finding is fundamental for understanding process-induced C impurity doping in MOCVD-grown 2D semiconductors and might have important implications for the functionality and performance of (opto)electronic devices.
Doping against the native propensity of MoS2: degenerate hole doping by cation substitution
Nano letters, 2014
Layered transition metal dichalcogenides (TMDs) draw much attention as the key semiconducting material for two-dimensional electrical, optoelectronic, and spintronic devices. For most of these applications, both n- and p-type materials are needed to form junctions and support bipolar carrier conduction. However, typically only one type of doping is stable for a particular TMD. For example, molybdenum disulfide (MoS2) is natively an n-type presumably due to omnipresent electron-donating sulfur vacancies, and stable/controllable p-type doping has not been achieved. The lack of p-type doping hampers the development of charge-splitting p-n junctions of MoS2, as well as limits carrier conduction to spin-degenerate conduction bands instead of the more interesting, spin-polarized valence bands. Traditionally, extrinsic p-type doping in TMDs has been approached with surface adsorption or intercalation of electron-accepting molecules. However, practically stable doping requires substitution ...
Doping mechanisms in graphene-MoS2 hybrids
Applied Physics Letters, 2013
We present a joint theoretical and experimental investigation of charge doping and electronic potential landscapes in hybrid structures composed of graphene and semiconducting single layer MoS2. From first-principles simulations we find electron doping of graphene due to the presence of rhenium impurities in MoS2. Furthermore, we show that MoS2 edges give rise to charge reordering and a potential shift in graphene, which can be controlled through external gate voltages. The interplay of edge and impurity effects allows the use of the graphene-MoS2 hybrid as a photodetector. Spatially resolved photocurrent signals can be used to resolve potential gradients and local doping levels in the sample.
Defects in layered vapor-phase grown MOS2
2017 75th Annual Device Research Conference (DRC), 2017
Molybdenum disulfide (MoS2) is a layered two-dimensional (2D) semiconducting material with a band-gap ranging from 1.3 eV in bulk to 1.88 eV in mono-layer [1]. This transition metal dichalcogenide (TMD) is being studied as a potential material for nanoelectronics and optoelectronics [2], [3]. Most of the research on electronic devices based on MoS2 published so far is naturally focused on lateral (in-plane) transport properties. In this work, we investigate MoS2 with respect to its material properties in vertical direction, with a potential application as a dielectric barrier material for vertical heterosturcture devices, such as Graphene-base Hot Electron Transistors (GBTs) [4], [5]. Its low band gap compared to available oxides and its low band offset with respect to silicon (Si) could yield an efficient GBT emission barrier [6]. We discuss Si/MoS2/Metal structures based on C-V measurements and propose the method for probing the electronic properties, including defects and interfa...
Physical Review Materials
Substitutional doping of two-dimensional semiconducting transition metal dichalcogenides such as MoS 2 offers a stable and promising route for tailoring their electrical, optical, and magnetic properties. We perform density functional theory calculations for two promising transition metal dopants, Re and Nb, and their defect complexes with intrinsic S vacancies in MoS 2. We compute the formation energy of each dopant and complex in different charge states utilizing a charge correction scheme that enables us to accurately predict the charge transition levels and complex binding energies, as well as characterize their electronic properties. We predict remarkably different behavior between Re and Nb dopants and their defect complexes: Re dopants can form complexes with S vacancies which quench the n-type doping of Re Mo , while Nb dopants are unlikely to form such complexes and their p-type doping properties appear to be less sensitive to the presence of S vacancies.
Carbon, 2016
Heterostructures of 2D materials are expected to become building blocks of next generation nanoelectronic devices. Therefore, the detailed understanding of their interfaces is of particular importance. In order to gain information on the properties of the graphene-MoS 2 system, we have investigated MoS 2 sheets grown by chemical vapour deposition (CVD) on highly ordered pyrolytic graphite (HOPG) as a model system with atomically clean interface. The results are compared with results reported recently for MoS 2 grown on epitaxial graphene on SiC. Our STM study revealed that the crystallographic orientation of MoS 2 sheets is determined by the orientation of the underlying graphite lattice. This epitaxial orientation preference is so strong that the MoS 2 flakes could be moved on HOPG with the STM tip over large distances without rotation. The electronic properties of the MoS 2 flakes have been investigated using tunnelling spectroscopy. A significant modification of the electronic structure has been revealed at flake edges and grain boundaries. These features are expected to have an important influence on the performance of nanoelectronic devices. We