We performed, for the first time, quantitative characterization of electron capture cross sections σ of the interface states at dielectric/III-N heterojunction interfaces. We developed a new method, which is based on the photo-assisted capacitance-voltage measurements using photon energies below the semiconductor band gap. The analysis was carried out for AlGaN/GaN metal-insulator-semiconductor heterojunction (MISH) structures with Al2O3, SiO2, or SiN films as insulator deposited on the AlGaN layers with Al content (x) varying over a wide range of values. Additionally, we also investigated an Al2O3/InAlN/GaN MISH structure. Prior to insulator deposition, the AlGaN and InAlN surfaces were subjected to different treatments. We found that σ for all these structures lies in the range between 5×10−19 and 10−16 cm2. Furthermore, we revealed that σ for dielectric/AlxGa1−xN interfaces increases with increasing x. We showed that both the multiphonon-emission and cascade processes can explain the obtained results.

The key feature for the precise tuning of V_th in GaN-based metal-insulator-semiconductor (MIS) high electron mobility transistors is the control of the positive fixed charge (Q_f) at the insulator/III-N interfaces, whose amount is often comparable to the negative surface polarization charge ($Q_{pol}^{-}$ ). In order to clarify the origin of Q_f, we carried out a comprehensive capacitance-voltage (C-V) characterization of SiO₂/Al_xGa_1–xN/GaN and SiN/Al_xGa_1–xN/GaN structures with Al composition (x) varying from 0.15 to 0.4. For both types of structures, we observed a significant V_th shift in C-V curves towards the positive gate voltage with increasing x. On the contrary, the Schottky gate structures exhibited V_th shift towards the more negative biases. From the numerical simulations of C-V curves using the Poisson's equation supported by the analytical calculations of V_th, we showed that the V_th shift in the examined MIS structures is due to a significant decrease in the positive Q_f with rising x. Finally, we examined this result with respect to various hypotheses developed in the literature to explain the origin of the positive Q_f at insulator/III-N interfaces.

Understanding the stability of magnetic textures in multilayer patterned dots would constitute a significant step toward skyrmion-based applications. Here, we report the observation of skyrmions in patterned nanodots composed of multilayers. We examine the stabilization of various magnetic states such as single-domain states, skyrmion states, horseshoe-like domain structures, and worm-like domain structures in submicrometer dots (diameters 150–525 nm). Dots are fabricated from Pt/Co/Au multilayer structures that exhibit the interfacial Dzyaloshinskii–Moriya interaction and perpendicular magnetic anisotropy. In particular, we show that a stack of six repetitions of Pt/Co/Au layers suffices to stabilize the skyrmion state inside a dot at room temperature. A micromagnetic simulation determines the regime of skyrmion stability. The results reveal a correlation between the magnetic-force microscopy measurements and the micromagnetic simulation. Furthermore, we explain the development of the magnetic state with increasing dot diameter. We envision that nanopatterning of multilayer magnetic films could serve as a versatile way of creating magnetic skyrmion states.

Properties of InAlN/GaN heterostructures and field-effect transistors with nearly lattice matched $(InN=18%)$ and tensely (13%) or compressively (21%) strained InAlN barrier layer were evaluated. The sheet charge density increased from $1.1×1013$ to $2.2×1013cm−2$ with decreased InN mole fraction. The saturation drain current as well as the peak extrinsic transconductance increased inversely proportional to the InN mole fraction—from 1 A/mm to 1.4 A/mm $(VG=2V)$ and from 190 to 230 mS/mm. On the other hand, the threshold voltage shifted to higher values with increased InN mole fraction. The pulsed current-voltage measurements (⁠ $1μs$ pulse width) yielded relatively low and nearly identical gate lag for all devices investigated. These results show that InAlN/GaN heterostructures with tensely strained InAlN can be useful for high-frequency and high-power devices and with compressively strained InAlN might be useful for the preparation of enhancement mode GaN-based devices.

The electrical properties of AlGaN/GaN MOSHFETs with HfO ₂ prepared by atomic layer deposition with and w/o oxygen-plasma treatment (further referred to as PHf-MOS and Hf-MOS) were investigated. The sub-threshold slope of the MOSHFETs (350 and 150 mV dec ⁻¹ for Hf-MOS and PHf-MOS, respectively) were lower than that for HFET (450 mV dec ⁻¹ ), which also correspond with lower leakage current of the MOSHFETs (∼10 ⁻⁸ A mm ⁻¹ at −9 V for PHf-MOS). In addition, the density of the interface states at the oxide/GaN-cap layer near the conduction band edge and mid-gap (∼5 × 10 ¹² and 2 × 10 ¹¹ cm ⁻² eV ⁻¹ , respectively) after PHf-MOS was lower than that for Hf-MOS (∼3 × 10 ¹³ and 2 × 10 ¹² cm ⁻² eV ⁻¹ , respectively). From the x-ray photoemission spectroscopy analysis we observed a shift in the Auger Ga LMM peaks (0.6 eV) and an increase of the intensity area of the Ga–O bond in the Ga2p3 spectrum after the oxygen-plasma treatment, mainly because the GaN-cap layer was oxidized and Ga ₂ O ₃ was formed.