Properties of Ga₂O₃ thin films deposited by electron‐beam evaporation from a high‐purity single‐crystal Gd₃Ga₅O₁₂ source are reported. As‐deposited Ga₂O₃ films are amorphous, stoichiometric, and homogeneous. Excellent uniformity in thickness and refractive index was obtained over a 2 in. wafer. The films maintain their integrity during annealing up to 800 and 1200 °C on GaAs and Si substrates, respectively. Optical properties including refractive index (n=1.84–1.88 at 980 nm wavelength) and band gap (4.4 eV) are close or identical, respectively, to Ga₂O₃ bulk properties. Reflectivities as low as 10⁻⁵ for Ga₂O₃/GaAs structures and a small absorption coefficient (≊100 cm⁻¹ at 980 nm) were measured. Dielectric properties include a static dielectric constant between 9.9 and 10.2, which is identical to bulk Ga₂O₃, and electric breakdown fields up to 3.6 MV/cm. The Ga₂O₃/GaAs interface demonstrated a significantly higher photoluminescence intensity and thus a lower surface recombination velocity as compared to Al₂O₃/GaAs structures.

${\mathrm{Al}}_2{\mathrm{O}}_3$ was deposited on ${\mathrm{In}}_{0.15}{\mathrm{Ga}}_{0.85}\mathrm{As}∕\mathrm{GaAs}$ using atomic-layer deposition (ALD). Without any surface preparation or postthermal treatment, excellent electrical properties of ${\mathrm{Al}}_2{\mathrm{O}}_3∕\mathrm{InGaAs}∕\mathrm{GaAs}$ heterostructures were obtained, in terms of low electrical leakage current density (${10}^{-8}$ to ${10}^{-9}\mathrm{A}∕{\mathrm{cm}}^2$ ) and low interfacial density of states $\left(D_{it}\right)$ in the range of ${10}^{12}{\mathrm{cm}}^{-2}{\mathrm{eV}}^{-1}$ . The interfacial reaction and structural properties studied by high-resolution x-ray photoelectron spectroscopy (HRXPS) and high-resolution transmission electron microscopy (HRTEM). The depth profile of HRXPS, using synchrotron radiation beam and low-energy ${\mathrm{Ar}}^{+}$ sputtering, exhibited no residual arsenic oxides at interface. The removal of the arsenic oxides from ${\mathrm{Al}}_2{\mathrm{O}}_3∕\mathrm{InGaAs}$ heterostructures during the ALD process ensures the Fermi-level unpinning, which was observed in the capacitance-voltage measurements. The HRTEM shows sharp transition from amorphous oxide to single crystalline semiconductor.

Measurements of the transport critical‐current density (J_c), magnetization J_c, and magnetoresistance in a number of bulk sintered samples of Y₁Ba₂Cu₃O_x from several different laboratories indicate that the transport J_c is limited by weak‐link regions between high J_c regions. The weak‐link J_c has a Josephson character, decreasing by two orders of magnitude as the magnetic field is increased from 0.1 to 10 mT at 77 K. An examination of the grain‐boundary region in Y₁Ba₂Cu₃O_x shows no observable impurities or second phases to the scale of the [001] lattice planes (∼12 Å). The effect of intrinsic conduction anisotropy is discussed. A current‐transfer model is proposed in which weak conduction along the c axis plays a role in limiting J_c at grain boundaries. Orienting the grains in the powder state during processing may result in enhanced transport J_c in bulk conductors.

A GaAs metal–oxide–semiconductor field-effect transistor (MOSFET) with thin Al2O3 gate dielectric in nanometer (nm) range grown by atomic layer deposition is demonstrated. The nm-thin oxide layer with significant gate leakage current suppression is one of the key factors in downsizing field-effect transistors. A 1 μm gate-length depletion-mode n-channel GaAs MOSFET with an Al2O3 gate oxide thickness of 8 nm, an equivalent SiO2 thickness of ∼3 nm, shows a broad maximum transconductance of 120 mS/mm and a drain current of more than 400 mA/mm. The device shows a good linearity, low gate leakage current, and negligible hysteresis in drain current in a wide range of bias voltage.

The optical functions of $\mathrm{\beta -}{\mathrm{Ga}}_2{\mathrm{O}}_3$ thin films have been determined by ellipsometry from 0.74–5 eV. Several electron-beam evaporated and rf magnetron sputtered films of different thicknesses were investigated using a multisample technique. Refractive index values comparable to those of bulk material are found. Cauchy dispersion model fits yield a high-frequency dielectric constant ${\epsilon }_{\infty }$ of 3.57. Above 4.7 eV a direct absorption edge is observed.