Al 2 O 3 was deposited on In 0.15 Ga 0.85 As/ GaAs using atomic-layer deposition ͑ALD͒. Without any surface preparation or postthermal treatment, excellent electrical properties of Al 2 O 3 / InGaAs/ GaAs heterostructures were obtained, in terms of low electrical leakage current density ͑10 −8 to 10 −9 A/cm 2 ͒ and low interfacial density of states ͑D it ͒ in the range of 10 12 cm −2 eV −1. The interfacial reaction and structural properties studied by high-resolution x-ray photoelectron spectroscopy ͑HRXPS͒ and high-resolution transmission electron microscopy ͑HRTEM͒. The depth profile of HRXPS, using synchrotron radiation beam and low-energy Ar + sputtering, exhibited no residual arsenic oxides at interface. The removal of the arsenic oxides from Al 2 O 3 / 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.

High HfO 2 was deposited on n-type GaN ͑0001͒ using atomic layer deposition with Hf͑NCH 3 C 2 H 5 ͒ 4 and H 2 O as the precursors. Excellent electrical properties of TiN / HfO 2 / GaN metal-oxide-semiconductor diode with the oxide thickness of 8.8 nm were obtained, in terms of low electrical leakage current density ͑ϳ10 −6 A/cm 2 at V FB +1 V͒, well behaved capacitance-voltage ͑C-V͒ curves having a low interfacial density of states of 2 ϫ 10 11 cm −2 eV −1 at the midgap, and a high dielectric constant of 16.5. C-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 ϳ1.8 nm thick, as probed using x-ray photoelectron spectroscopy.

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Hexagonal-phase single-crystal Gd2 O3 is deposited on GaN in a molecular beam epitaxy system. The dielectric constant is about twice that of its cubic counterpart when deposited on InGaAs or Si. The capacitive effective thickness of 0.5 nm in hexagonal Gd2 O3 is perhaps the lowest on GaN-metal-oxide-semiconductor devices. The heterostructure is thermo dynamically stable at high temperatures and exhibits low interfacial densities of states after high-temperature annealing.

High κ dielectric of HfAlO/HfO2 was an in-situ atomic-layer-deposited directly on molecular beam epitaxy grown In0.53Ga0.47As surface without using pre-treatments or interfacial passivation layers, where HfAlO (HfO2:Al2O3 ∼ 4:1) with high re-crystallization temperature was employed as the top oxide layer. The HfAlO (∼4.5 nm)/HfO2 (0.8 nm)/In0.53Ga0.47As metal oxide semiconductor capacitors have exhibited an oxide/In0.53Ga0.47As interface free of arsenic-related defective bonding, thermodynamic stability at 800 °C, and low leakage current densities of <10−7 A/cm2 at ±1 MV/cm. The interfacial trap density (Dit) spectra in absence of mid-gap peaks were obtained by temperature-dependent capacitance and conductance with Dit’s of 2–3 × 1012 eV−1 cm−2 below and 6–12 × 1011 eV−1 cm−2 above the mid-gap of In0.53Ga0.47As, respectively. An equivalent oxide thickness of less than 1 nm has been achieved by reducing the HfAlO thickness to ∼2.7 nm with the same initial HfO2 thickness of ∼0.8 nm.