For the integration of two-dimensional (2D) transition metal dichalcogenides (TMDC) with high-performance electronic systems, one of the greatest challenges is the realization of doping and comprehension of its mechanisms. Low-temperature atomic layer deposition of aluminum oxide is found to n-dope MoS2 and ReS2 but not WS2. Based on electrical, optical, and chemical analyses, we propose and validate a hypothesis to explain the doping mechanism. Doping is ascribed to donor states in the band gap of Al x O y , which donate electrons or not, based on the alignment of the electronic bands of the 2D TMDC. Through systematic experimental characterization, incorporation of impurities (e.g., carbon) is identified as the likely cause of such states. By modulating the carbon concentration in the capping oxide, doping can be controlled. Through systematic and comprehensive experimental analysis, this study correlates, for the first time, 2D TMDC doping to the carbon incorporation on dielectric encapsulation layers. We highlight the possibility to engineer dopant layers to control the material selectivity and doping concentration in 2D TMDC.

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Electron band alignment at interfaces of SiO2 with directly synthesized few-monolayer (ML) thin semiconducting MoS2 films is characterized by using field-dependent internal photoemission of electrons from the valence band of MoS2 into the oxide conduction band. We found that reducing the grown MoS2 film thickness from 3 ML to 1 ML leads to ≈400 meV downshift of the valence band top edge as referenced to the common energy level of the SiO2 conduction band bottom. Furthermore, comparison of the MoS2 layers grown by a H-free process (sputtering of Mo in sulfur vapor) to films synthesized by sulfurization of metallic Mo in H2S indicates a significant (≈500 meV) electron barrier increase in the last case. This effect is tentatively ascribed to the formation of an interface dipole due to the interaction of hydrogen with the oxide surface.

Density Functional Theory simulations have been used to identify the structural factors that define the material properties of OTS. They show that the nature of the mobility-gap states in amorphous Ge-rich Ge50Se50 is related to Ge-Ge bonds, whereas in Se-rich Ge30Se70 -Ge valence-alternating-pairs and Se lone-pairs are dominating. To obtain a faithful description of the electronic structure, delocalization of states, it is required to combine hybrid exchangecorrelation functionals with large unit-cell models. The extent of the localization of the electronic states depends on the applied external electric field. Hence, OTS materials undergo structural changes during the electrical cycling of the device, with a decrease in the population of less exothermic Ge-Ge bonds in favor of more exothermic Ge-Se. This reduces the amount of charge traps, which translates into coordination changes, increase in mobility-gap and subsequently changes the selector device electrical parameters. The threshold voltage drift process can be explained by the natural evolution of the non-preferred Ge-Ge bonds (or

The article overviews experimental results obtained by applying Internal PhotoEmission (IPE) spectroscopy methods to characterize electron states in single-or few-monolayer twodimensional (2D) materals and at their interfaces. Several conducting (graphene) and semiconducting (transitional metal dichalcogenides MoS2, WS2, MoSe2, and WSe2) films have been analyzed by IPE, which reveals significant sensitivity of interface band offsets and barriers to the details of the material and interface fabrication indicating violation of the Schottky-Mott rule. This variability is associated with charges and dipoles formed at the interfaces with van der Waals bonding as opposed to the chemically bonded interfaces of three-dimensional semiconductors and metals. Chemical modification of the underlying SiO2 surface is shown to be a significant factor, affecting interface barriers due to violation of the interface electroneutrality.

Internal photoemission of electrons (IPE) from large area one monolayer 2H-MoS 2 films synthesized on top of amorphous (aÀ) SiO 2 or Al 2 O 3 is used to determine the energy of the semiconductor valence band (VB) relative to the reference level of the insulator conduction band (CB). This allows us to compare the VB top energy in MoS 2 to that of the (100)Si substrate crystal at the interface with the same insulator. Despite the CB in a-Al 2 O 3 is found to be %1 eV below that in SiO 2 as measured relative to the Si VB edge, the authors observe nearly no shift of the spectral threshold in the case of IPE from the MoS 2 VB. This observation indicates violation of electroneutrality at the MoS 2 /a-Al 2 O 3 interface causing an increase in barrier by %1 eV. This conclusion is supported by the much weaker field dependence of the IPE threshold at the MoS 2 /a-Al 2 O 3 interface compared to the MoS 2 /a-SiO 2 one, suggesting the presence of negative charges and/or interface dipoles. Therefore, the commonly accepted electron affinity rule (EAR) appears to be not appropriate to describe the band alignment at 2D/insulator interfaces.

We present a defect spectroscopy technique to profile the energy and spatial distribution of defects within a material stack from leakage current (J-V), capacitance (C-V) and conductance (G-V) measurements. The technique relies on the concept of sensitivity maps (SM), that identify the band-gap regions where defects affect those electrical characteristics. The information provided by SMs are used to reproduce J-V, C-V and G-V data measured at different temperatures and frequencies by means of physics-based simulations relying on an accurate description of carriers-defect interactions. The proposed defect spectroscopy technique is applied to ZrO2-based metal-insulator-metal structures of different composition for DRAM capacitor applications. The origin of the observed voltage, temperature and frequency dependencies of the I-V, C-V and G-V data is understood and the atomic structure of the relevant stack defects is identified.

Exploring the thickness-dependent electronic properties of ultrathin transition metal dichalcogenides is crucial for novel optoelectronic devices. Particularly important is experimental information regarding the bandgap width. This information is scarce and often inconsistent among the several measurement techniques that were employed for this task, such as optical absorption, scanning tunneling spectroscopy and photoconductivity. Here, we present photoconductivity measurements in large-area synthetic MoS 2 and WS 2 films (1-5 monolayers and the bulk crystal) grown on insulating layers (SiO 2 , Al 2 O 3 or HfO 2 ). The excitonic peaks of MoS 2 and WS 2 were detected in both the photocapacitor and traditional in-plane geometries.Their contribution to the photoconductivity is explained by the electric field-assisted dissociation mechanism. We have separated the excitonic and free carrier components in the photocurrent spectra, and extracted the direct and indirect bandgaps using the Tauc plot, revealing their dependencies on the number of monolayers.