High $\kappa$ $\mathrm{Hf}{\mathrm{O}}_2$ was deposited on $n$ -type GaN (0001) using atomic layer deposition with $\mathrm{Hf}{\left(\mathrm{N}\mathrm{C}{\mathrm{H}}_3{\mathrm{C}}_2{\mathrm{H}}_5\right)}_4$ and ${\mathrm{H}}_2\mathrm{O}$ as the precursors. Excellent electrical properties of $\mathrm{Ti}\mathrm{N}∕\mathrm{Hf}{\mathrm{O}}_2∕\mathrm{Ga}\mathrm{N}$ metal-oxide-semiconductor diode with the oxide thickness of $8.8\mathrm{nm}$ were obtained, in terms of low electrical leakage current density ($\sim {10}^{-6}\mathrm{A}∕{\mathrm{cm}}^2$ at $V_{\mathrm{FB}}+1\mathrm{V}$ ), well behaved capacitance-voltage $\left(C\text{-}V\right)$ curves having a low interfacial density of states of $2\times {10}^{11}{\mathrm{cm}}^{-2}{\mathrm{eV}}^{-1}$ at the midgap, and a high dielectric constant of 16.5. $C\text{-}V$ curves with clear accumulation and depletion behaviors were shown, along with negligible frequency dispersion and hysteresis with sweeping biasing voltages. The structural properties studied by high-resolution transmission electron microscopy and x-ray reflectivity show an atomically smooth oxide/GaN interface, with an interfacial layer of GaON $\sim 1.8\mathrm{nm}$ thick, as probed using x-ray photoelectron spectroscopy.

Atomic-layer-deposited high $\kappa$ dielectric $\mathrm{Hf}{\mathrm{O}}_2$ films on air-exposed ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}∕\mathrm{In}\mathrm{P}$ (100), using $\mathrm{Hf}{\left(\mathrm{N}\mathrm{C}{\mathrm{H}}_3{\mathrm{C}}_2{\mathrm{H}}_5\right)}_4$ and ${\mathrm{H}}_2\mathrm{O}$ as the precursors, were found to have an atomically sharp interface free of arsenic oxides, an important aspect for Fermi level unpinning. A careful and thorough probing, using high-resolution angular-resolved x-ray photoelectron spectroscopy (XPS) with synchrotron radiation, however, observed the existence of ${\mathrm{Ga}}_2{\mathrm{O}}_3$ , ${\mathrm{In}}_2{\mathrm{O}}_3$ , and $\mathrm{In}{\left(\mathrm{O}\mathrm{H}\right)}_3$ at the interface. The current transport of the metal-oxide-semiconductor capacitor for an oxide $7.8\mathrm{nm}$ thick follows the Fowler–Nordheim tunneling mechanism and shows a low leakage current density of $\sim {10}^{-8}\mathrm{A}∕{\mathrm{cm}}^2$ at $V_{\mathrm{FB}}+1\mathrm{V}$ . Well behaved frequency-varying capacitance-voltage curves were measured and an interfacial density of states of $2\times {10}^{12}{\mathrm{cm}}^{-2}{\mathrm{eV}}^{-1}$ was derived. A conduction-band offset of $1.8\pm 0.1\mathrm{eV}$ and a valence-band offset of $2.9\pm 0.1\mathrm{eV}$ have been determined using the current transport data and XPS, respectively.

Harnessing the spin–momentum locking of topological surface states in conjunction with magnetic materials is the first step to realize novel topological insulator-based devices. Here, we report strong interfacial coupling in Bi₂Se₃/yttrium iron garnet (YIG) bilayers manifested as large interfacial in-plane magnetic anisotropy (IMA) and enhancement of damping probed by ferromagnetic resonance. The interfacial IMA and damping enhancement reaches a maximum when the Bi₂Se₃film approaches its two-dimensional limit, indicating that topological surface states play an important role in the magnetization dynamics of YIG. Temperature-dependent ferromagnetic resonance of Bi₂Se₃/YIG reveals signatures of the magnetic proximity effect ofT_Cas high as 180 K, an emerging low-temperature perpendicular magnetic anisotropy competing the high-temperature IMA, and an increasing exchange effective field of YIG steadily increasing toward low temperature. Our study sheds light on the effects of topological insulators on magnetization dynamics, essential for the development of topological insulator-based spintronic devices.

X-ray photoelectron spectroscopy (XPS) combined with reflection electron energy loss spectroscopy (REELS) were used to determine the energy-band parameters, valence-band offsets $\Delta E_V$ , conduction-band offsets $\Delta E_C$ , and energy-band gaps $E_g$ , of the atomic layer deposited (ALD) ${\text{Al}}_2{\text{O}}_3$ and ${\text{HfO}}_2$ on ${\text{In}}_x{\text{Ga}}_{1-x}\text{As}$ ($x=0$ , 0.15, 0.25, and 0.53). Using REELS, $E_g$ values of the ${\text{ALD-Al}}_2{\text{O}}_3$ and $–{\text{HfO}}_2$ were estimated to be 6.77 and $5.56\pm 0.05\text{eV}$ , respectively. The $\Delta E_V$ ’s were determined by measuring the core level to valence band maximum binding energy difference from the XPS spectra. The $\Delta E_C$ ’s were then extracted from $\Delta E_V$ ’s and the energy-band gaps of the oxides and ${\text{In}}_x{\text{Ga}}_{1-x}\text{As}$ , and are in good agreement with those estimated from the Fowler–Nordheim tunneling. The $\Delta E_C$ ’s and $\Delta E_V$ ’s are larger than 1.5 and 2.5 eV, respectively, for all the ALD-oxide/${\text{In}}_x{\text{Ga}}_{1-x}\text{As}$ samples.

Thulium iron garnet (TmIG) films with perpendicular magnetic anisotropy (PMA) were grown on gadolinium gallium garnet (GGG) (111) substrates by off-axis sputtering. High-resolution synchrotron radiation X-ray diffraction studies and spherical aberration-corrected scanning transmission electron microscope (Cs-corrected STEM) images showed the excellent crystallinity of the films and their sharp interface with GGG. Damping constant of TmIG thin film was determined to be 0.0133 by frequency-dependent ferromagnetic resonance (FMR) measurements. The saturation magnetization (M_s) and the coercive field (H_c) were obtained systematically as a function of the longitudinal distance (L) between the sputtering target and the substrate. A 170% enhancement of PMA field (H_⊥) was achieved by tuning the film composition to increase the tensile strain. Moreover, current-induced magnetization switching on a Pt/TmIG structure was demonstrated with an ultra-low critical current density (j_c) of 2.5 × 10⁶ A/cm², an order of magnitude smaller than the previously reported value. We were able to tune M_s, H_c and H_⊥ to obtain an ultra-low j_c of switching the magnetization, showing the great potential of sputtered TmIG films for spintronics.