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.

Atomic layer deposition (ALD) of high-κ dielectrics on two-dimensional (2D) materials (including graphene and transition metal dichalcogenides) still represents a challenge due to the lack of out-of-plane bonds on the pristine surfaces of 2D materials, thus making the nucleation process highly disadvantaged. The typical methods to promote the nucleation (i.e., the predeposition of seed layers or the surface activation via chemical treatments) certainly improve the ALD growth but can affect, to some extent, the electronic properties of 2D materials and the interface with high-κ dielectrics. Hence, direct ALD on 2D materials without seed and functionalization layers remains highly desirable. In this context, a crucial role can be played by the interaction with the substrate supporting the 2D membrane. In particular, metallic substrates such as copper or gold have been found to enhance the ALD nucleation of Al₂O₃ and HfO₂ both on monolayer (1 L) graphene and MoS₂. Similarly, uniform ALD growth of Al₂O₃ on the surface of 1 L epitaxial graphene (EG) on SiC (0001) has been ascribed to the peculiar EG/SiC interface properties. This review provides a detailed discussion of the substrate-driven ALD growth of high-κ dielectrics on 2D materials, mainly on graphene and MoS₂. The nucleation mechanism and the influence of the ALD parameters (namely the ALD temperature and cycle number) on the coverage as well as the structural and electrical properties of the deposited high-κ thin films are described. Finally, the open challenges for applications are discussed.

The dielectric breakdown (BD) kinetics of praseodymium thin films has been determined by comparison between current-voltage measurements on large-area (up to 78.54μm2) metal-oxide-semiconductor structures and conductive-atomic force microscopy (C-AFM). C-AFM clearly images the weak BD single spots under constant voltage stresses. The stress time on the single C-AFM tip dot was varied from 2.5×10−3 to 8×10−2s. The density of BD spots, upon increasing the stress time, exhibits an exponential trend. The Weibull slope and the characteristic time of the dielectric BD have been determined by direct measurements at nanometer scale.

In this paper, the authors demonstrate the atomic layer deposition (ALD) of highly homogeneous and ultrathin (≈3.6 nm) Al₂O₃ films with very good insulating properties (breakdown field of ≈10–12 MV cm⁻¹) directly onto monolayer (1L) MoS₂ exfoliated on gold. Differently than in the case of 1L MoS₂ supported by a common insulating substrate (Al₂O₃/Si), a better nucleation process of the high‐k film is observed on the 1L MoS₂/Au system since the ALD early stages. Atomic force microscopy analyses show a ≈50% Al₂O₃ surface coverage just after 10 ALD cycles, its increase to >90% (after 40 cycles), and a uniform ≈3.6 nm film (after 80 cycles). The Al₂O₃ density on bilayer MoS₂ is found to be significantly reduced with respect to 1L MoS₂/Au, suggesting a role of screened interface charges with the metal substrate on the adsorption of ALD precursors. Finally, Raman and photoluminescence spectroscopy show a p‐type doping and tensile strain of 1L MoS₂ induced by the Au substrate, providing an insight on the evolution of vibrational and optical properties after the Al₂O₃ deposition. The direct ALD growth of Al₂O₃ on large‐area 1L MoS₂ induced by the Au underlayer can be of wide interest for electronic applications.