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In this letter, treatment of GaAs surface by using dimethylaluminumhydride-derived AlON passivation layer prior to HfO2 deposition is proposed to solve the issue of Fermi level pinning. It has been found that AlON passivation layer effectively suppresses the oxides formation and leads to the Fermi level unpinning at the interface between GaAs and HfO2. Based on analysis from metal-oxide-semiconductor capacitors of Au/HfO2/AlON/GaAs stack, excellent capacitance-voltage characteristics with saturated accumulation capacitance and reduced leakage current have been achieved, which may originate from the decrease in the interface state density and the increase in the conduction band offset. [ABSTRACT FROM AUTHOR]

Fermi level pinning attributed to oxides at the GaAs/high-k interface is a major obstacle to develop GaAs-based metal-oxide-semiconductor devices with high performance. In this letter, thermal nitridation treatment of GaAs surface prior to the high-k deposition is proposed to solve the issue of interface pinning. Results have confirmed that nitridation passivation effectively suppresses the oxides formation and leads to a shift in the Fermi level toward the conduction band minimum on the GaAs surface, which increases the conduction band offset at the GaAs/AlOxNy interface, followed by a saturated accumulation capacitance with reduced gate leakage current. [ABSTRACT FROM AUTHOR]

The effect of nitrogen atom doping on the optical properties and dielectric constant of HfO2 films has been systematically investigated. Spectroscopic ellipsometry was employed to investigate the optical properties of nitrogen incorporated HfO2 films. The values of average oscillator strength and average oscillator position extracted from spectroscopic ellipsometry demonstrated that nitrogen incorporation could influence the dipole oscillator strength and oscillator position of HfO2. A physical model of dipole structures was proposed to verify the enhancement of dielectric constant of HfO2 films by nitrogen incorporation. [ABSTRACT FROM AUTHOR]

The effect of N concentration on the band gap and band offsets of HfOxNy films has been systematically investigated. It was found that the band gap as well as the band offsets of HfOxNy films decreased with the increase of N concentration. When the N concentration reached 16.3%, the conduction band offset (ΔEc) reduced to be 0.88 eV, which is smaller than the minimal requirement of ΔEc values for high-k dielectrics and, thus, leads to unacceptably high leakage currents. Therefore, nitrogen concentration should be carefully controlled to guarantee excellent properties of nitrogen incorporated high-k dielectrics. [ABSTRACT FROM AUTHOR]

Effects of nitrogen incorporation on interfacial property, band gap, and band alignments of high-k Y2O3 gate dielectrics have been investigated. It was found that the incorporation of nitrogen into Y2O3 films can effectively suppress the growth of the interfacial layer between Y2O3 and Si substrate. The incorporation of nitrogen into Y2O3 films leads to the reduction of band gap and valence band offset, but not the conduction offset of Y2O3 films. High temperature annealing will help to increase the band gap and valence band offset of YOxNy film due to the release of the interstitial N atoms. [ABSTRACT FROM AUTHOR]

Temperature-dependent interfacial chemical bonding states and band alignment of HfOxNy/SiO2/Si gate stacks have been investigated by X-ray photoemission spectroscopy (XPS) and spectroscopic ellipsometry (SE). By means of the chemical shifts of Hf 4f, Si 2p, O 1s, and N 1s core-level spectra, it has been found that the chemical stability of the HfOxNy/SiO2/Si stacks strongly depends on the annealing temperature. Analysis of temperature-dependent band alignment of HfOxNy/SiO2/Si stacks suggests that the valence band offset ΔEv increases slowly from 1.82 eV for as-grown film to 2.55 eV for annealed film at 700 °C; however, the values of conduction band offset ΔEc only demonstrates a slight change in the vicinity of 1.50 eV. From the band offset viewpoint, HfOxNy/SiO2/Si gate stack could be a promising candidate for high-k gate dielectrics. [ABSTRACT FROM AUTHOR]

A ZrO2/TiO2/Si gate stack has been prepared by using solid phase reaction between sputtered ZrO2/Ti stack and underlying SiO2/Si substrate through in situ vacuum annealing. X-ray photoelectron spectroscopy was used to analyze interfacial properties of the ZrO2/TiO2/Si stack after annealing at high temperatures. The interfacial silicate is composed of Ti silicate and ZrO2 layer does not take part in the interfacial reaction to form Zr silicate. Such a stack has the advantage of combining high dielectric constant of ZrO2 and excellent interfacial property of Ti silicate/Si interface, and will have potential applications in the advanced metal-oxide-semiconductor devices. [ABSTRACT FROM AUTHOR]

One-dimensional chains consisting of crystalline Fe3O4 nanoparticles have been synthesized by using a polyacrylic acid template method. The characterizations of composition, structure, and magnetic property of the chains are performed. The formation mechanism of Fe3O4 nanocrystal chains is proposed to be a polymer template and magnetostatic interaction. In a weak magnetic field, the synthesized nanochains can be reorganized. The as-synthesized nanochains are ferromagnetic at room temperature with lower saturation magnetization and higher coercivity value than those of bulk Fe3O4, which could have potential applications in nanosensors for rapid and sensitive detection of biologic or chemical molecules. [ABSTRACT FROM AUTHOR]

Thermal stability and energy-band alignment of ZrOxNy films on Si are investigated using x-ray photoelectron spectroscopy and spectroscopy elliposometry (SE). The results show that the Zr–N bonds in as-oxidized ZrOxNy films are thermally unstable, while the N–O bonds in ZrOxNy matrix are stable even at high annealing temperature of 900 °C. Optical properties are also analyzed based on the SE fitting results. The slight blueshift in the absorption edge indicates the increased band gap from 3.9 to 5.1 eV after the additional annealing. Based on the valence-band spectrum results, zero-field energy-band alignments for ZrOxNy/Si and ZrOxNy/SiO2/Si stacks are extracted. [ABSTRACT FROM AUTHOR]

We report in this letter that Hafnium oxynitride (HfOxNy) gate dielectrics were prepared by radio frequency (RF) reactive magnetron sputtering and optical properties of the HfOxNy thin films were investigated by spectroscopic ellipsometry with photon energy of 0.75–6.5 eV at room temperature. The investigations showed that the annealing temperatures have a strong effect on the optical properties of HfOxNy thin films. With increased annealing temperature, the refractive index n is observed to increase, while the extinction coefficient k decreases, respectively. The changes of the complex dielectric functions and the optical band gap Eg with the annealing temperature are also discussed. [ABSTRACT FROM AUTHOR]

The optical properties of δ-Bi2O3 thin films were investigated using spectroscopic ellipsometry and optical absorption spectrum. δ-Bi2O3 thin films were grown on Si and quartz substrates under different oxygen flow ratios (OFR) by radio frequency reactive magnetron sputtering. The Tauc-Lorentz dispersion method was adopted to model the optical dispersion functions of the thin films. The optical bandgap was obtained by three different methods. It was found that refractive index and extinction coefficient decrease, and the optical bandgap has a slight blue shift with increasing the OFR. Factors influencing the optical constants and optical bandgap are discussed. [ABSTRACT FROM AUTHOR]

Monoclinic structured β-Ga2O3 nanobelts have been synthesized through a simple thermochemical route at low temperature in range of 400–500 °C. Each nanobelt has a uniform width of about several hundred nanometers and a thickness of about 10 nm along its entire length. Micro-Raman spectrum of the β-Ga2O3 nanobelts shows that the four weak Raman bands at 112, 146, 170, and 266 cm-1 which seem to correspond to infrared (IR)-active transverse optical (TO) Au mode and/or longitudinal optical (LO) Bu mode, respectively. The IR-active bands in the Raman spectrum and the surface mode in the IR spectrum may relate to the nanoscale morphology of the nanobelts. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry with photon energy 0.75–6.5 eV at room temperature has been used to derive the optical properties of nitrogen-incorporated HfO2 films on Si(100) substrates grown by radio-frequency reactive sputtering using different N2/(N2+O2+Ar) gas ratios from 20% to 50%. Excellent agreement has been found between the experimental and the simulated spectra, in which an empirical dielectric dispersion relation based on Tauc-Lorentz model has been successfully adopted. Increases in the refractive index n and the extinction coefficient. k, with increases in nitrogen-incorporation content are observed due to the nitrogen-incorporation-induced higher packing density. The change of the complex dielectric functions and reduction in the optical band gap with an increase in nitrogen concentration resulting from the effect of the nitrogen-incorporation on the structure are discussed in detail. [ABSTRACT FROM AUTHOR]

Monoclinic gallium oxide (β-Ga[sub 2]O[sub 3]) nanowires were synthesized by heat treating a composite material of GaAs and pre-evaporated Au at 1240 °C in dry oxygen atmosphere. The catalytic Au metal generated liquid nanoclusters that serve as reactive sites confining and directing the growth of β-Ga[sub 2]O[sub 3] nanowires during the vapor-liquid-solid growth process. The β-Ga[sub 2]O[sub 3] nanowires have diameters ranging from 20 to 50 nm and lengths of several micrometers. Photoluminescence measurement under excitation at 250 nm shows that the bulk β-Ga[sub 2]O[sub 3] nanowires have a stable blue emission at 475 nm and an ultraviolet emission at 330 nm, which may be related to the defects such as the oxygen vacancy and the gallium-oxygen vacancy pair. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Highly ordered TiO[sub 2] nanowire (TN) arrays were prepared in anodic alumina membranes (AAMs) by a sol-gel method. The TNs are single crystalline anatase phase with uniform diameters around 60 nm. At room temperature, photoluminescence (PL) measurements of the TN arrays show a visible broadband with three peaks, which are located at about 425, 465, and 525 nm that are attributed to self-trapped excitons, F, and F[sup +] centers, respectively. A model is also presented to explain the PL intensity drop-down of the TN arrays embedded in AAMs: the blue PL band of AAMs arises from the F[sup +] centers on the pore walls, and the TNs first form in the center area of the pores and then extend to the pore walls. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]