Semiconducting transition metal dichalcogenides (TMDs) are promising materials for future electronic and optoelectronic applications. However, their electronic properties are strongly affected by peculiar nanoscale defects/inhomogeneities (point or complex defects, thickness fluctuations, grain boundaries, etc.), which are intrinsic of these materials or introduced during device fabrication processes. This paper reviews recent applications of conductive atomic force microscopy (C-AFM) to the investigation of nanoscale transport properties in TMDs, discussing the implications of the local phenomena in the overall behavior of TMD-based devices. Nanoscale resolution current spectroscopy and mapping by C-AFM provided information on the Schottky barrier uniformity and shed light on the mechanisms responsible for the Fermi level pinning commonly observed at metal/TMD interfaces. Methods for nanoscale tailoring of the Schottky barrier in MoS₂ for the realization of ambipolar transistors are also illustrated. Experiments on local conductivity mapping in monolayer MoS₂ grown by chemical vapor deposition (CVD) on SiO₂ substrates are discussed, providing a direct evidence of the resistance associated to the grain boundaries (GBs) between MoS₂ domains. Finally, C-AFM provided an insight into the current transport phenomena in TMD-based heterostructures, including lateral heterojunctions observed within Mo_xW_1–xSe₂ alloys, and vertical heterostructures made by van der Waals stacking of different TMDs (e.g., MoS₂/WSe₂) or by CVD growth of TMDs on bulk semiconductors.

This letter reports on the negative charge trapping in Al₂O₃ thin films grown by atomic layer deposition onto oxidized silicon carbide (4H-SiC). The films exhibited a permittivity of 8.4, a breakdown field of 9.2 MV/cm and small hysteresis under moderate bias cycles. However, severe electron trapping inside the Al₂O₃ film (1 × 10¹² cm⁻²) occurs upon high positive bias stress (>10V). Capacitance-voltage measurements at different temperatures and stress conditions have been used to determine an activation energy of 0.1eV. The results provide indications on the possible nature of the trapping defects and, hence, on the strategies to improve this technology for 4H-SiC devices.

Semiconductor transition metal dichalcogenides (TMDs), such as MoS₂, are currently regarded as key‐enabling materials for sub‐1 nm channel transistors, beyond‐complementary metal–oxide–semiconductor electronic and optoelectronic devices and sensors. Owing to this wide application potential, several bottom‐up and top‐down synthesis approaches for these materials have been explored so far. Despite the huge progresses in scalable deposition methods (such as chemical vapor deposition, metal–organic chemical vapor deposition), exfoliated layers from bulk crystals still represent the benchmark for record electronic properties of TMDs. Among exfoliation approaches, metal‐assisted mechanical exfoliation emerges as the most effective method to separate large‐area (mm² to cm²) single‐crystalline monolayer membranes of TMDs (and many other 2D materials) from the parent bulk crystals. This paper reviews the state‐of‐the‐art in this field, from current understanding of MoS₂ exfoliation mechanisms on Au (considered as a model system), to the main device applications of as‐exfoliated and transferred large‐area MoS₂ membranes (including Au/MoS₂/Au memristors, MoS₂ photodetectors, and field‐effect transistors). Perspectives of this method in the realization of arrays of 2D heterojunction devices, including Moirè superlattice devices, and open challenges for its widespread application are finally discussed.

The gold-assisted exfoliation is a very effective method to produce large-area (cm²-scale) membranes of molybdenum disulfide (MoS₂) for electronics. However, the strong MoS₂/Au interaction, beneficial for the exfoliation process, has a strong impact on the vibrational and light emission properties of MoS₂. Here, we report an atomic force microscopy, micro-Raman, and micro-photoluminescence (μ-PL) investigation of 2H-MoS₂ with variable thickness exfoliated on Au and subsequently transferred on an Al₂O₃/Si substrate. The E_2g–A_1g vibrational mode separation Δω (typically used to estimate MoS₂ thickness) exhibits an anomalous large value (Δω ≈ 21.2 cm⁻¹) for monolayer (1L) MoS₂ on Au as compared to the typical one (Δω ≈ 18.5 cm⁻¹) measured on 1L MoS₂ on Al₂O₃. Such substrate-related differences, explained in terms of tensile strain and p-type doping arising from the MoS₂/Au interaction, were found to gradually decrease while increasing the number of MoS₂ layers. Furthermore, μ-PL spectra for 1L MoS₂ on Au exhibit a strong quenching and an overall redshift of the main emission peak at 1.79 eV, compared to the 1.84 eV peak for 1L MoS₂ on Al₂O₃. After PL spectra deconvolution, such redshift was explained in terms of a higher trion/exciton intensity ratio, probably due to the higher polarizability of the metal substrate, as well as to the smaller equilibrium distance at the MoS₂/Au interface.

In this paper, we report a multiscale investigation of the compositional, morphological, structural, electrical, and optical emission properties of 2H-MoS2 obtained by sulfurization at 800 °C of very thin MoO3 films (with thickness ranging from ~2.8 nm to ~4.2 nm) on a SiO2/Si substrate. XPS analyses confirmed that the sulfurization was very effective in the reduction of the oxide to MoS2, with only a small percentage of residual MoO3 present in the final film. High-resolution TEM/STEM analyses revealed the formation of few (i.e., 2–3 layers) of MoS2 nearly aligned with the SiO2 surface in the case of the thinnest (~2.8 nm) MoO3 film, whereas multilayers of MoS2 partially standing up with respect to the substrate were observed for the ~4.2 nm one. Such different configurations indicate the prevalence of different mechanisms (i.e., vapour-solid surface reaction or S diffusion within the film) as a function of the thickness. The uniform thickness distribution of the few-layer and multilayer MoS2 was confirmed by Raman mapping. Furthermore, the correlative plot of the characteristic A1g-E2g Raman modes revealed a compressive strain (ε ≈ −0.78 ± 0.18%) and the coexistence of n- and p-type doped areas in the few-layer MoS2 on SiO2, where the p-type doping is probably due to the presence of residual MoO3. Nanoscale resolution current mapping by C-AFM showed local inhomogeneities in the conductivity of the few-layer MoS2, which are well correlated to the lateral changes in the strain detected by Raman. Finally, characteristic spectroscopic signatures of the defects/disorder in MoS2 films produced by sulfurization were identified by a comparative analysis of Raman and photoluminescence (PL) spectra with CVD grown MoS2 flakes.

High-κ dielectrics are insulating materials with higher permittivity than silicon dioxide. These materials have already found application in microelectronics, mainly as gate insulators or passivating layers for silicon (Si) technology. However, since the last decade, the post-Si era began with the pervasive introduction of wide band gap (WBG) semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), which opened new perspectives for high-κ materials in these emerging technologies. In this context, aluminium and hafnium oxides (i.e., Al₂O₃, HfO₂) and some rare earth oxides (e.g., CeO₂, Gd₂O₃, Sc₂O₃) are promising high-κ binary oxides that can find application as gate dielectric layers in the next generation of high-power and high-frequency transistors based on SiC and GaN. This review paper gives a general overview of high-permittivity binary oxides thin films for post-Si electronic devices. In particular, focus is placed on high-κ binary oxides grown by atomic layer deposition on WBG semiconductors (silicon carbide and gallium nitride), as either amorphous or crystalline films. The impacts of deposition modes and pre- or postdeposition treatments are both discussed. Moreover, the dielectric behaviour of these films is also presented, and some examples of high-κ binary oxides applied to SiC and GaN transistors are reported. The potential advantages and the current limitations of these technologies are highlighted.