M. L. Huang

Energy-band parameters of atomic-layer-deposition Al2O3∕InGaAs heterostructure

The valence-band offset has been determined to be 3.83±0.05eV at the atomic-layer-deposition Al2O3∕InGaAs interface by x-ray photoelectron spectroscopy. The Au–Al2O3∕InGaAs metal-oxide-semiconductor diode exhibits current-voltage characteristics dominated by Fowler-Nordheim tunneling. From the current-voltage data at forward and reverse biases, a conduction-band offset of 1.6±0.1eV at the Al2O3–InGaAs interface and an electron effective mass ∼0.28±0.04m0 of the Al2O3 layer have been extracted. Consequently, combining the valence-band offset, the conduction-band offset, and the energy-band gap of the InGaAs, the energy-band gap of the atomic-layer-deposited Al2O3 is 6.65±0.11eV.

Atomic-layer-deposited HfO2 on In0.53Ga0.47As: Passivation and energy-band parameters

Atomic-layer-deposited high κ dielectric HfO2 films on air-exposed In0.53Ga0.47As∕InP (100), using Hf(NCH3C2H5)4 and H2O 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 Ga2O3, In2O3, and In(OH)3 at the interface. The current transport of the metal-oxide-semiconductor capacitor for an oxide 7.8nm thick follows the Fowler–Nordheim tunneling mechanism and shows a low leakage current density of ∼10−8A∕cm2 at VFB+1V. Well behaved frequency-varying capacitance-voltage curves were measured and an interfacial density of states of 2×1012cm−2eV−1 was derived. A conduction-band offset of 1.8±0.1eV and a valence-band offset of 2.9±0.1eV have been determined using the current transport data and XPS, respectively.

Structural and electrical characteristics of atomic layer deposited high κ HfO2 on GaN

High κ HfO2 was deposited on n-type GaN (0001) using atomic layer deposition with Hf(NCH3C2H5)4 and H2O as the precursors. Excellent electrical properties of TiN∕HfO2∕GaN metal-oxide-semiconductor diode with the oxide thickness of 8.8nm were obtained, in terms of low electrical leakage current density (∼10−6A∕cm2 at VFB+1V), well behaved capacitance-voltage (C-V) curves having a low interfacial density of states of 2×1011cm−2eV−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 ∼1.8nm thick, as probed using x-ray photoelectron spectroscopy.

Structural and electrical characteristics of atomic layer deposited high kappa HfO2 on GaN

High κ HfO2 was deposited on n-type GaN (0001) using atomic layer deposition with Hf(NCH3C2H5)4 and H2O as the precursors. Excellent electrical properties of TiN∕HfO2∕GaN metal-oxide-semiconductor diode with the oxide thickness of 8.8nm were obtained, in terms of low electrical leakage current density (∼10−6A∕cm2 at VFB+1V), well behaved capacitance-voltage (C-V) curves having a low interfacial density of states of 2×1011cm−2eV−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 ∼1.8nm thick, as probed using x-ray photoelectron spectroscopy.

Energy-band parameters of atomic layer deposited Al2O3 and HfO2 on InxGa1−xAs

X-ray photoelectron spectroscopy (XPS) combined with reflection electron energy loss spectroscopy (REELS) were used to determine the energy-band parameters, valence-band offsets ΔEV, conduction-band offsets ΔEC, and energy-band gaps Eg, of the atomic layer deposited (ALD) Al2O3 and HfO2 on InxGa1−xAs (x=0, 0.15, 0.25, and 0.53). Using REELS, Eg values of the ALD-Al2O3 and –HfO2 were estimated to be 6.77 and 5.56±0.05 eV, respectively. The ΔEV’s were determined by measuring the core level to valence band maximum binding energy difference from the XPS spectra. The ΔEC’s were then extracted from ΔEV’s and the energy-band gaps of the oxides and InxGa1−xAs, and are in good agreement with those estimated from the Fowler–Nordheim tunneling. The ΔEC’s and ΔEV’s are larger than 1.5 and 2.5 eV, respectively, for all the ALD-oxide/InxGa1−xAs samples.

Achieving 1nm capacitive effective thickness in atomic layer deposited HfO2 on In0.53Ga0.47As

A capacitive effective thickness (CET) value of 1.0nm has been achieved in atomic layer deposited (ALD) high κ dielectrics HfO2 on In0.53Ga0.47As∕InP. The key is a short air exposure under 10min between removal of the freshly grown semiconductor epilayers and loading to the ALD reactor. This has led to minimal formation of the interfacial layer thickness, as confirmed using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. The measured electrical characteristics of metal-oxide-semiconductor diodes of Au∕Ti∕HfO2(4.5nm)∕In0.53Ga0.47As showed a low leakage current density of 3.8×10−4A∕cm2 at VFB+1V, which is about eight orders of magnitudes lower than that of SiO2 with the same CET. The capacitance-voltage curves show an overall κ value of 17–18, a nearly zero flatband shift, and an interfacial density of states Dit of 2×1012cm−2eV−1.A capacitive effective thickness (CET) value of 1.0nm has been achieved in atomic layer deposited (ALD) high κ dielectrics HfO2 on In0.53Ga0.47As∕InP. The key is a short air exposure under 10min between removal of the freshly grown semiconductor epilayers and loading to the ALD reactor. This has led to minimal formation of the interfacial layer thickness, as confirmed using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. The measured electrical characteristics of metal-oxide-semiconductor diodes of Au∕Ti∕HfO2(4.5nm)∕In0.53Ga0.47As showed a low leakage current density of 3.8×10−4A∕cm2 at VFB+1V, which is about eight orders of magnitudes lower than that of SiO2 with the same CET. The capacitance-voltage curves show an overall κ value of 17–18, a nearly zero flatband shift, and an interfacial density of states Dit of 2×1012cm−2eV−1.

Realization of high-quality HfO{sub 2} on In{sub 0.53}Ga{sub 0.47}As by in-situ atomic-layer-deposition

High {kappa} dielectric of HfAlO/HfO{sub 2} was an in-situ atomic-layer-deposited directly on molecular beam epitaxy grown In{sub 0.53}Ga{sub 0.47}As surface without using pre-treatments or interfacial passivation layers, where HfAlO (HfO{sub 2}:Al{sub 2}O{sub 3} {approx} 4:1) with high re-crystallization temperature was employed as the top oxide layer. The HfAlO ({approx}4.5 nm)/HfO{sub 2} (0.8 nm)/In{sub 0.53}Ga{sub 0.47}As metal oxide semiconductor capacitors have exhibited an oxide/In{sub 0.53}Ga{sub 0.47}As interface free of arsenic-related defective bonding, thermodynamic stability at 800 deg. C, and low leakage current densities of <10{sup -7} A/cm{sup 2} at {+-}1 MV/cm. The interfacial trap density (D{sub it}) spectra in absence of mid-gap peaks were obtained by temperature-dependent capacitance and conductance with D{sub it}s of 2-3 x 10{sup 12} eV{sup -1} cm{sup -2} below and 6-12 x 10{sup 11} eV{sup -1} cm{sup -2} above the mid-gap of In{sub 0.53}Ga{sub 0.47}As, respectively. An equivalent oxide thickness of less than 1 nm has been achieved by reducing the HfAlO thickness to {approx}2.7 nm with the same initial HfO{sub 2} thickness of {approx}0.8 nm.

Cubic HfO2 doped with Y2O3 epitaxial films on GaAs (001) of enhanced dielectric constant

Nanometer thick cubic HfO2 doped with 19at.% Y2O3 (YDH) epitaxial films were grown on GaAs (001) using molecular beam epitaxy. Structural studies determined the epitaxial orientation relationships between the cubic YDH films and GaAs to be (001)GaAs∕∕(001)YDH and [100]GaAs∕∕[100]YDH. The YDH structure is strain relaxed with a lattice constant of 0.5122nm with a small mosaic spread of 0.023° and a twist angle of 2.9°. The YDH/GaAs interface is atomically abrupt without evidence of reacted interfacial layers. From C-V and I-V measurements a 7.7nm thick YDH film has an enhanced dielectric constant κ∼32, an equivalent oxide thickness of ∼0.94nm, an interfacial state density Dit∼7×1012cm−2eV−1, and a low leakage current density of 6×10−5A∕cm2 at 1V gate bias.

Effective passivation of In0.2Ga0.8As by HfO2 surpassing Al2O3 via in-situ atomic layer deposition

High κ gate dielectrics of HfO2 and Al2O3 were deposited on molecular beam epitaxy-grown In0.2Ga0.8As pristine surface using in-situ atomic-layer-deposition (ALD) without any surface treatment or passivation layer. The ALD-HfO2/p-In0.2Ga0.8As interface showed notable reduction in the interfacial density of states (Dit), deduced from quasi-static capacitance-voltage and conductance-voltage (G-V) at room temperature and 100 °C. More significantly, the midgap peak commonly observed in the Dit(E) of ALD-oxides/In0.2Ga0.8As is now greatly diminished. The midgap Dit value decreases from ≥15 × 1012 eV−1 cm−2 for ALD-Al2O3 to ∼2–4 × 1012 eV−1 cm−2 for ALD-HfO2. Further, thermal stability at 850 °C was achieved in the HfO2/In0.2Ga0.8As, whereas C-V characteristics of Al2O3/p-In0.2Ga0.8As degraded after the high temperature annealing. From in-situ x-ray photoelectron spectra, the AsOx, which is not the oxidized state from the native oxide, but is an induced state from adsorption of trimethylaluminum and H2O, was fo...

Ga2O3(Gd2O3) on Ge without interfacial layers: Energy-band parameters and metal oxide semiconductor devices

Ga2O3(Gd2O3) (GGO) directly deposited on Ge substrate in ultrahigh vacuum, without a passivation layer such as GeOxNy or Si, has demonstrated excellent electrical performances and thermodynamic stability. Energy-band parameters of GGO/Ge have been determined by in situ x-ray photoelectron spectroscopy in conjunction with reflection electron energy loss spectroscopy and current transport of Fowler–Nordheim tunneling. A conduction-band offset and a valence-band offset of ∼2.3 and ∼2.42 eV, respectively, have been obtained. Moreover, self-aligned Ge pMOSFETs of 1-μm-gate length using Al2O3/GGO as the gate dielectrics have shown a high drain current and a peak transconductance of 252 mA/mm, and 143 mS/mm, respectively.