T. D. Lin

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.

High-performance self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistor with Al2O3∕Ga2O3(Gd2O3) as gate dielectrics

Self-aligned inversion-channel In0.53Ga0.47As metal-oxide-semiconductor field-effect transistors (MOSFETs) using ultrahigh-vacuum deposited Al2O3∕Ga2O3(Gd2O3) (GGO) dual-layer dielectrics and a TiN metal gate were fabricated. For a In0.53Ga0.47As MOSFET using a gate dielectric of Al2O3(2nmthick)∕GGO(5nmthick), a maximum drain current of 1.05A∕mm, a transconductance of 714mS∕mm, and a peak mobility of 1300cm2∕Vs have been achieved, the highest ever reported for III-V inversion-channel devices of 1μm gate length.

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.

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.

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.

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...

Attainment of low interfacial trap density absent of a large midgap peak in In0.2Ga0.8As by Ga2O3(Gd2O3) passivation

The pronounced high interfacial densities of states (Dit) commonly observed around the midgap energy of dielectric/GaAs interfaces are generally considered the culprit responsible for the poor electrical performance of the corresponding inversion-channel metal-oxide-semiconductor field-effect-transistors. In this work, comprehensive Dit spectra as the function of energy [Dit(E)] inside the In0.2Ga0.8As band gap were constructed by using the quasistatic capacitance-voltage and the temperature-dependent conductance method on n- and p-type ultrahigh vacuum (UHV)-Ga2O3(Gd2O3)/In0.2Ga0.8As and atomic-layer-deposited (ALD)-Al2O3/In0.2Ga0.8As metal-oxide-semiconductor capacitors. Unlike the ALD-Al2O3/In0.2Ga0.8As interface giving a Dit spectrum with a high midgap Dit peak, the UHV-Ga2O3(Gd2O3)/In0.2Ga0.8As interface shows a Dit spectrum that monotonically decreases from the valence band to the conduction band with no discernible midgap peak.The pronounced high interfacial densities of states (Dit) commonly observed around the midgap energy of dielectric/GaAs interfaces are generally considered the culprit responsible for the poor electrical performance of the corresponding inversion-channel metal-oxide-semiconductor field-effect-transistors. In this work, comprehensive Dit spectra as the function of energy [Dit(E)] inside the In0.2Ga0.8As band gap were constructed by using the quasistatic capacitance-voltage and the temperature-dependent conductance method on n- and p-type ultrahigh vacuum (UHV)-Ga2O3(Gd2O3)/In0.2Ga0.8As and atomic-layer-deposited (ALD)-Al2O3/In0.2Ga0.8As metal-oxide-semiconductor capacitors. Unlike the ALD-Al2O3/In0.2Ga0.8As interface giving a Dit spectrum with a high midgap Dit peak, the UHV-Ga2O3(Gd2O3)/In0.2Ga0.8As interface shows a Dit spectrum that monotonically decreases from the valence band to the conduction band with no discernible midgap peak.

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.

Growth mechanism of atomic layer deposited Al2O3 on GaAs(001)-4 × 6 surface with trimethylaluminum and water as precursors

A microscopic view of in situatomic layer deposition Al2O3 on clean n-GaAs (001)-4 × 6 surfaces probed by high-resolution synchrotron radiation photoemission is presented. The precursors of trimethylaluminum (TMA) and water partially and selectively bond with the surface atoms without disturbing the atoms in the subsurface layer. The first-cycle TMA acts differently on the surface As atoms; namely, TMA is dissociative on As in the As-Ga dimer but is physisorbed on As that is 3-fold Ga coordinated. Water drastically alters the TMA-covered surface to etch off the dissociated TMA with As, giving Ga–O bonding for the later deposition of Al2O3 and at the same time to transform the configuration of the physisorbed TMA to bond strongly with As. Approximately six cycles of purges (TMA + water) are required before the interaction at the interface is complete. In comparison, the e-beam deposition of Al2O3 on GaAs greatly disturbs the III-Vsurface so that a high As 4+ charge state appears and the surface Ga atoms become clustered.

Approaching fermi level unpinning in Oxide-In0.2Ga0.8As

Electrical characteristics of oxide-In_0.2Ga_0.8As interface in ultra-high vacuum (UHV)-deposited Al₂O₃(3 nm)/Ga₂O₃ (Gd₂O₃) (8.5 nm) on n- and p-In_0.2Ga_0.8As/GaAs are studied. Capacitance-voltage (<i>C-V</i>) measurements under light illumination and under wide range of temperatures as well as corresponding conductance-voltage (<i>G-V</i>) measurements were carried out. Extremely high-quality interfaces with free-moving Fermi-level near the conductance and valence band-edges (regions close to E_c and E_v) are revealed for the Ga₂O₃(Gd₂O₃)/In_0.2Ga_0.8As system.