Evidence of Native Cs Impurities and Metal–Insulator Transition in MoS 2 Natural Crystals (original) (raw)
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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...
Ab-initio study on the possible doping strategies for MoS2 monolayers
Density functional theory is used to systematically study the electronic and magnetic properties of doped MoS2 monolayers, where the dopants are incorporated both via S/Mo substitution or as adsorbates. Among the possible substitutional dopants at the Mo site, Nb is identified as suitable p-type dopant, while Re is the donor with the lowest activation energy. When dopants are simply adsorbed on a monolayer we find that alkali metals shift the Fermi energy into the MoS2 conduction band, making the system n-type. Finally, the adsorption of charged molecules is considered, mimicking an ionic liquid environment. We find that molecules adsorption can lead to both n-and p-type conductivity, depending on the charge polarity of the adsorbed species.
Review Article Two-dimensional MoS2 as a new material for electronic devices
2016
Abstract: We overview fundamental properties, preparation techniques, and potential device applications of single-and few-monolayer-thick molybdenum disulde MoS2 belonging to a new emerging class of materials: 2-dimensional semiconductors. To a large extent, the interest in the 2-dimensional materials is fueled by the quest for alternatives to graphene, which is hardly suitable for electronic devices because of the lack of a band gap. A unique combination of physical properties, including exibility, high electron mobility, and optical transparency combined with a large band gap tunable from indirect 1.2 eV for bulk to direct 1.9 eV for a monolayer, make MoS2 attractive for a variety of electronic and optoelectronic devices. The rst device demonstrations are very encouraging: eld-eect transistors with high current ON/OFF ratios, high-sensitivity phototransistors, logic circuits, and ampliers based on monolayer-MoS2 have been demonstrated. The layered structure of MoS2 with other tran...
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 ...
Electronic and optical properties of 2D monolayer (ML) MoS2 with vacancy defect at S sites
Nano-Structures & Nano-Objects, 2019
Herein, we have studied the electronic and optical properties of S-sites vacancy defect monolayer (ML) MoS 2 from density functional theory (DFT) based on the linear combination of atomic orbitals (LCAO). ML-MoS 2 is an intrinsic semiconductor having direct electronic band gap of ∼1.82 eV. This system is highly sensitive to vacancy defect due to the significant changes in characteristics of fully occupied and unoccupied orbitals near Fermi energy (E F). On increasing the concentration of random vacancy defects ML-MoS 2 exhibits a diminishing semiconducting band gap. Also the profile of electronic band gap changes from direct to indirect as well as the shifting of the E F. The semiconducting behaviour is preserved up to 25% vacancy defects, above which occurs a semiconductor-metal transition. These features arise due to the Mod and S-p states and attributed to the photoluminescence for making MoS 2 a promising material for opto-electronic devices. To investigate the opto-electronic response we have calculated the dielectric function (ϵ), refractive index (n), and absorption coefficient (α) as a function of incident photon energy (hω).
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.
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...
Unveiling the origin of n-type doping of natural MoS2: carbon
npj 2D Materials and Applications
MoS2 has attracted intense interest in many applications. Natural MoS2 and field-effect transistors made of it generally exhibit n-type characteristics, but its origin is unknown. Herein, we show that C is the origin of the universal n-type doping of natural MoS2. Photoemission spectroscopies reveal that while many MoS2 samples with C detected are n-type, some without C exhibit p-type characteristics. The C-free, p-type MoS2 changes to n-type over time with the concurrent appearance of C that is out-diffused from bulk, indicating that C induces the n-type doping. The C-origin is verified by C-deposition and supported by theoretical calculations. This carbon appears as nanometer-scale defects frequently observed in scanning tunneling microscopy. In addition, we propose, based on the calculations, that S vacancies are responsible for the p-type characteristics, which contrasts with the widespread belief. This work provides new perspectives on MoS2 doping and presents a new direction f...
Atomic Structure and Spectroscopy of Single Metal (Cr, V) Substitutional Dopants in Monolayer MoS2
ACS nano, 2016
Dopants in two-dimensional dichalcogenides have a significant role in affecting electronic, mechanical, and interfacial properties. Controllable doping is desired for the intentional modification of such properties to enhance performance; however, unwanted defects and impurity dopants also have a detrimental impact, as often found for chemical vapor deposition (CVD) grown films. The reliable identification, and subsequent characterization, of dopants is therefore of significant importance. Here, we show that Cr and V impurity atoms are found in CVD grown MoS2 monolayer 2D crystals as single atom substitutional dopants in place of Mo. We attribute these impurities to trace elements present in the MoO3 CVD precursor. Simultaneous annular dark field scanning transmission electron microscopy (ADF-STEM) and electron energy loss spectroscopy (EELS) is used to map the location of metal atom substitutions of Cr and V in MoS2 monolayers with single atom precision. The Cr and V are stable und...