Monolayer transition metal dichalcogenides are novel, gapped two-dimensional materials with unique electrical and optical properties. Toward device applications, we consider MoS2 layers on dielectrics, in particular in this work, the effect of vacancies on the electronic structure. In density-functional based simulations, we consider the effects of near-interface O vacancies in the oxide slab, and Mo or S vacancies in the MoS2 layer. Band structures and atomprojected densities of states for each system and with differing oxide terminations were calculated, as well as those for the defect-free MoS2-dielectrics system and for isolated dielectric layers for reference. Among our results, we find that with O vacancies, both the Hf-terminated HfO2-MoS2 system, and the O-terminated and H-passivated Al2O3-MoS2 systems appear metallic due to doping of the oxide slab followed by electron transfer into the MoS2, in manner analogous to modulation doping. The n-type doping of monolayer MoS2 by high-k oxides with oxygen vacancies then is experimentally demonstrated by electrically and spectroscopically characterizing back-gated monolayer MoS2 field effect transistors encapsulated by oxygen deficient alumina and hafnia.
AUTHOR INFORMATIONCorresponding Author *Amithraj Valsaraj: amithrajv@utexas.edu ACKNOWLEDGMENT This work is supported by SEMATECH, the Nanoelectronics Research Initiative (NRI) through the Southwest Academy of Nanoelectronics (SWAN), and Intel. We thank the Texas Advanced Computing Center (TACC) for computational support.
Using an ab initio density functional theory based electronic structure method with a semilocal density approximation, we study thin-film electronic properties of two topological insulators based on ternary compounds of Tl (thallium) and Bi (bismuth). We consider TlBiX 2 (X = Se, Te) and Bi 2 X 2 Y (X,Y = Se,Te) compounds which provide better Dirac cones, compared to the model binary compounds Bi 2 X 3 (X = Se, Te). With this property in combination with a structurally perfect bulk crystal, the latter ternary compound has been found to have improved surface electronic transport in recent experiments. In this article, we discuss the nature of surface states, their locations in the Brillouin zone and their interactions within the bulk region. Our calculations suggest a critical thin film thickness to maintain the Dirac cone which is significantly smaller than that in binary Bi-based compounds. Atomic relaxations or rearrangements are found to affect the Dirac cone in some of these compounds. And with the help of layer-projected surface charge densities, we discuss the penetration depth of the surface states into the bulk region. The electronic spectrum of these ternary compounds agrees very well with the available experimental results.
We study the transport properties of deeply scaled monolayer MoS 2 n-channel metal-oxidesemiconductor field effect transistors (MOSFETs) using full-band ballistic quantum transport simulations with an atomistic tight-binding Hamiltonian obtained from density functional theory.Our simulations suggest that monolayer MoS 2 MOSFETs can provide near-ideal subthreshold slope, and suppression of drain-induced barrier lowering (DIBL) and gate-induced drain leakage (GIDL). However, these full-band simulations also exhibit limited transconductance. These ballistic simulations also exhibit negative differential resistance (NDR) in the output characteristics associated with the narrow width in energy of the lowest conduction band, but this NDR may be substantially reduced or eliminated by scattering in MoS 2 .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.