Patrick Fiorenza

The electrical behavior of SiO ₂ /4H‐SiC interfaces is a central challenge for the development of high‐efficiency MOSFETs, where trap states and interfacial structural distortions can affect carrier mobility and device reliability. In this work, we investigate thermally grown SiO ₂ on n‐type 4H‐SiC epilayers, analyzing the effects of different post‐oxidation annealings (POAs) in N ₂ and Ar on both the electrical response and the interfacial strain. MOS capacitors subjected to POA in N ₂ exhibit a marked reduction of interface states density (D _it ) near the conduction band edge, together with an increase of the electron Fowler–Nordheim barrier height. These electrical signatures occur simultaneously with negative flat‐band voltage shifts, suggesting the presence of an interfacial dipole rather than the presence of fixed charges only. Raman spectroscopy reveals that N ₂ ‐based POA induces an increase of biaxial tensile strain at the SiO ₂ /SiC interface, which is less pronounced in the case of POA in Ar. The observation of strain evolution and electrical properties demonstrates that nitrogen incorporation not only passivates dangling bonds but also modifies the interfacial stress state, thereby influencing barrier properties and charge distribution. These findings provide new insights to be considered in the optimization of SiO ₂ /SiC gate stacks in 4H‐SiC MOSFETs.

An Al₂O₃/AlN stack deposited via Atomic Layer Deposition (ALD) methods as a gate insulator for silicon carbide (4H-SiC) has been investigated, focusing on the effects of different Al₂O₃ deposition processes on the nitride layer. In particular, dielectric stacks, consisting of a 10 nm AlN interface (001)-oriented layer directly grown on a 4H–SiC substrate and in 20 nm of additional amorphous Al₂O₃ layers were synthesized in sequential deposition runs by thermal ALD (T-ALD) or plasma-enhanced ALD (PEALD) methods. The evolution of the phenomena occurring at the Al₂O₃/AlN interfaces has been established by in situ ellipsometry measurements. Strong effects of the oxygen plasma because of the O-Al-N bond formation have been clearly observed and corroborated by ex situ structural and electrical characterizations, especially in the case of the plasma-enhanced Al₂O₃ process. In particular, the Al₂O₃/AlN bilayer grown by the Al₂O₃ T-ALD method exhibited good insulating behavior and an 8.7-high dielectric constant was measured. By contrast, the Al₂O₃/AlN bilayer grown by the Al₂O₃ PEALD method demonstrated poor insulating properties.

In this work, the electrical properties of Mo ₂ C/4H-SiC Schottky contacts were studied at different annealing temperatures. In particular, the Schottky barrier height was derived by current-voltage measurements on as-deposited and 400 °C and 700 °C-annealed contacts. The Schottky barrier height was comparable for the as-deposited and 400°C-annealed Mo ₂ C/4H-SiC contact (0.94 and 0.96 eV, respectively), while it increased (1.07 eV) for the 700 °C-annealed Mo ₂ C/4H-SiC one. For the sample annealed at 700°C, the electrical characterization of the diodes was combined with the study of the surface and interface electrical properties, by Kelvin-probe force microscopy (KPFM) and frequency dependent capacitance-voltage measurements (C-f-V) and discussed assuming a Mo/4H-SiC Schottky contact (F _B =1.39 eV) as a reference. The KPFM measurements revealed a similar value of the surface potential, thus suggesting that the work function of the metal is the same in both cases. On the other hand, a higher density of interface state was obtained by C-f-V for the Mo ₂ C/4H-SiC system. This latter can explain the reduction of the Schottky barrier height observed for this system.

Silicon carbide (SiC) has emerged as a leading material for high-power applications. However, the high density of interface states (D _it ) at the SiO ₂ /SiC interface still constrains the performance and reliability of MOSFET devices. In this work, lateral 4H-SiC MOSFETs subjected to post-deposition annealing (PDA) in nitric oxide (NO) of different durations were investigated through capacitance-voltage measurements, supported by an analytical model and an iterative MATLAB-based D _it extraction algorithm. The results demonstrate that NO PDA effectively reduces D _it not only near the conduction band edge but also towards the valence band, yielding improved channel mobility (µ _FE ) and enhanced threshold voltage stability.

Basal plane dislocations (BPDs) represent one of the most detrimental defects in 4H-SiC epitaxial wafers, causing forward voltage degradation in bipolar and power FET devices through the formation and expansion of Shockley-type stacking faults (SSFs). This expansion is driven by the recombination-enhanced dislocation glide (REDG) mechanism during forward bias operation. Despite efforts to mitigate BPD effects by converting them into threading edge dislocations (TEDs) via buffer layer engineering, throughout the epitaxial growth SSFs can still nucleate and propagate, particularly under high current injection. This work presents a comprehensive analysis combining electrical characterization, fault localization technique, Scanning Electron Microscopy (SEM) and micro-photoluminescence (μ-PL) to investigate SSF formation, crystallographic features, and their impact on device performance. The results underscore the critical role of advanced diagnostics and epitaxial process optimization in controlling SSF-related degradation and improving the reliability of SiC power devices.

The integration of 2D molybdenum disulfide (MoS ₂ ) with gallium nitride (GaN) enables many interesting (opto)electronic applications, such as heterojunction diodes and UV/visible photodetectors, whose performances crucially depend on the thickness uniformity, strain and doping of MoS ₂ films and on the energy band alignment at the interface. This work reports a multiscale electro‐optical characterization of large size (∼100 µm) monolayer (1L) MoS ₂ flakes directly grown on n‐GaN and, for comparison, on a SiO ₂ /Si substrate by liquid‐precursors‐intermediated chemical vapor deposition. XPS and micro‐Raman mapping revealed a superior crystalline quality, lower average strain ε ≈ −0.06% and higher n‐type doping n ≈ 0.7 × 10 ¹³ cm ⁻² for 1L‐MoS ₂ grown on GaN, as compared to MoS ₂ grown under identical conditions on the amorphous SiO ₂ surface. Nanoscale current‐voltage mapping by C‐AFM showed a significantly reduced Schottky barrier (Φ _B = 0.57 ± 0.06 eV) at 1L‐MoS ₂ /GaN interface as compared to the bare GaN surface. This result, combined with a MoS ₂ /n‐GaN work function difference W _MoS2 ‐W _GaN ≈ 360 meV evaluated by KPFM mapping, revealed a type‐I band alignment at the heterojunction. Finally, photocurrent measurements on macroscopic Ni/n‐GaN, Ni/MoS ₂ /n‐GaN and Ni/MoS ₂ /SiO ₂ lateral devices under illumination with photon energies from ∼2 to ∼5 eV showed superior electro‐optical performances of Ni/MoS ₂ /n‐GaN heterojunctions both in the visible and UV range.

Strain‐dependent electronic and optical properties are one of the most appealing features of 2D semiconductors, like monolayer (1L) MoS ₂ . However, measuring and controlling the homogeneity of strain within the channel is crucial for next‐generation MoS ₂ field‐effect transistors (FETs). This article reports a multiscale investigation of backgated FETs fabricated using large‐area 1L MoS ₂ flakes grown by liquid‐precursor‐intermediated chemical vapor deposition on SiO ₂ /Si substrates. The devices exhibit very attractive properties for ultra‐low power applications, such as an I _on / I _off > 10 ⁶ and a normally off electrical behavior. The combination of temperature‐dependent analyses of the FET transfer characteristics and nanoscale resolution potential mapping by Kelvin probe force microscopy shows a fully depleted MoS ₂ channel at V _G = 0 and an effective Schottky barrier Φ _B,FB = 0.21 eV at flatband voltage V _FB = 17.9 V. An inhomogeneous tensile strain ( ε ) distribution along the channel length is revealed by micro‐Raman and photoluminescence (PL) mapping, with a reduced ε and blue‐shifted PL energy close to the Ni/Au source/drain contacts, suggesting a biaxial compression of 1L MoS ₂ induced by metal deposition. The implications of these observations on the effective mass m _eff variation along the channel and the current injection from source/drain contacts have been discussed in the perspective of future ultra‐scaled‐devices applications.

This paper reports on the effect of a sulfurization thermal process of the silicon carbide surface on the properties of Ni/4H-SiC Schottky barrier. In particular, the incorporation of sulfur (S) in the 4H-SiC near-surface region was observed at the process performed at 800 °C, without any significant effect on the surface morphology. On the other hand, Ni/4H-SiC Schottky contacts fabricated on the sulfurized 4H-SiC surface showed a 0.3 eV reduction of the average barrier height with a narrower distribution, with respect to the untreated sample. These results were explained by an increase of the 4H-SiC electron affinity after sulfurization, and a Fermi level pinning effect.