[en] We report the unusual photoluminescence (PL) properties of vertically aligned InN nanorod arrays grown on Si(111) with a Si₃N₄ buffer layer. The optimum growth conditions of InN nanorods are obtained by controlling the III/V ratio and the growth temperature. Structural characterization by X-ray diffraction and scanning electron microscopy indicates that individual nanorods are wurtzite InN single crystals with the growth direction along the c-axis. Near-infrared PL from InN nanorods is clearly observed at room temperature. However, in comparison to the PL from InN epitaxial films, the PL from InN nanorods is significantly lower in efficiency and exhibit anomalous temperature dependence. We propose that these unusual PL properties are results of considerable structural disorder (especially for the low-temperature grown InN nanorods) and strong surface electron accumulation effect. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] We demonstrate that vertically aligned InN nanorods can be grown on Si(111) by plasma-assisted molecular-beam epitaxy. Detailed structural characterization indicates that individual nanorods are wurtzite InN single crystals with the growth direction along the c axis. Near-infrared photoluminescence (PL) from InN nanorods can be clearly observed at room temperature. However, in comparison to the InN epitaxial films, the PL efficiency is significantly lower. Moreover, the variable-temperature PL measurements of InN nanorods exhibit anomalous temperature effects. We propose that these unusual PL properties are results of considerable structural disorder (especially for the low-temperature grown InN nanorods) and strong surface electron accumulation effects

[en] Charge transfer ΔQ = 0.35e at the Si-N bond in silicon nitride is determined experimentally using photoelectron spectroscopy, and the ionic formula of silicon nitride Si₃^+1.4N₄^-1.05 is derived. The electronic structure of α-Si₃N₄ is studied ab initio using the density functional method. The results of calculations (partial density of states) are compared with experimental data on X-ray emission spectroscopy of amorphous Si₃N₄. The electronic structure of the valence band of amorphous Si₃N₄ is studied using synchrotron radiation at different excitation energies. The electron and hole effective masses m_e^* ∼ m_h^* ∼ 0.5m_e are estimated theoretically. The calculated values correspond to experimental results on injection of electrons and holes into silicon nitride.

[en] The exact solution of the Thomas-Fermi equation for a planar accumulation layer of a degenerate semiconductor is presented. The obtained results are compared with theoretical literature data. The applicability of the solution is demonstrated by using results of electrochemical capacitance-voltage measurements and photoluminescence data for n-InN epilayers. It has been found that the difference between the electron concentrations estimated from the Hall and photoluminescence measurements is a measure of the electron content in the accumulation layer with acceptable accuracy. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] High-quality InN epitaxial films have been grown by nitrogen-plasma-assisted molecular-beam epitaxy on Si(111) substrates using a double-buffer technique. Growth of a (0001)-oriented single crystalline wurtzite-InN layer was confirmed by reflection high-energy electron diffraction, x-ray diffraction, and Raman scattering. At room temperature, these films exhibited strong near-infrared (0.6-0.9 eV) photoluminescence (PL). In addition to the optical absorption measurement of absorption edge and direct band nature, the PL signal was found to depend linearly on the excitation laser intensity over a wide intensity range. These results indicate that the observed PL is due to the emission of direct band-to-band recombination rather than the band-to-defect (or impurity) deep emission

[en] The refractive index and optical absorption of wurzite InN epilayers grown on Si(111) substrates with a β-Si₃N₄/AlN(0001) double-buffer by nitrogen-plasma-assisted molecular-beam epitaxy were studied by employing spectroscopic ellipsometry (SE). The crystalline quality of the InN epilayers were investigated by cross-sectional transmission electron microscopy, X-ray diffraction, and scanning electron microscopy. SE results analyzed by the Adachi's model for the dielectric function show that the optical absorption edge of InN varies in the range of 0.76-0.83 eV depending on the carrier concentration, which in turn can be adjusted by the thickness of the AlN buffer layer

[en] Effects of proton irradiation on the optical and electrical properties of n-InN with charge carrier concentrations of 2-5 x 10¹⁸ cm^-3 have been investigated. Strong changes in photoluminescence spectra and electrical parameters of irradiated n-InN are discussed. Proton irradiation of n-InN results in the appearance of shallow donors in large concentrations. Comparison with the effects observed on heavily degenerate n-InN after proton irradiation leads to the conclusion that these irradiation-produced donors are native defects, most likely vacancies on the nitrogen sublattice. (Abstract Copyright [2007], Wiley Periodicals, Inc.)

[en] It is shown that a study of the dependence of impurity-related resonant first-order Raman scattering on the frequency of excitation light makes it possible to observe the dispersion of polar optical and acoustic branches of vibrational spectrum in hexagonal InN within a wide range of wave vectors. It is established that the wave vectors of excited phonons are uniquely related to the energy of excitation photon. Frequencies of longitudinal optical phonons E₁(LO) and A₁(LO) in hexagonal InN were measured in the range of excitation-photon energies from 2.81 to 1.17 eV and the frequencies of longitudinal acoustic phonons were measured in the range 2.81-1.83 eV of excitation-photon energies. The obtained dependences made it possible to extrapolate the dispersion of phonons A₁(LO) and E₁(LO) to as far as the point Γ in the Brillouin zone and estimate the center-band energies of these phonons (these energies have not been uniquely determined so far).

[en] We demonstrate that InN quantum dots (QDs) can be spontaneously formed on AlN and GaN surfaces by plasma-assisted molecular-beam epitaxy under the Stranski-Krastanow (S-K) mode. Both Si(111) wafers and metal-organic chemical vapor deposition grown GaN/Al₂O₃(0001) templates were used as substrates in this work. Silicon is particularly interesting as a substrate for InN QD applications because of its electrical conductivity and transparency in the near-infrared. By using reflection high-energy electron diffraction (RHEED), the formation process of InN QDs can be monitored in situ. We observed the 2D-3D transition of S-K growth mode and the lattice constant varied dramatically at the 2D-3D transition point from AlN to InN lattice constant. Furthermore, from the ex situ atomic force microscopy and scanning electron microscopy measurements, we directly imaged InN QDs on the AlN surface with an average diameter of ∼ 14 nm and high areal density of ∼ 1.6 x 10¹¹ cm^-2

[en] Raman and SIMS studies of Mg-doped InN films with a Mg content from N_Mg=3.3 x 10¹⁹ to 5.5 x 10²¹ cm^-3 are reported. Lattice dynamics of hexagonal InN with substitutional impurities and vacancies has been investigated theoretically and calculated Raman spectra were compared with experimental ones. It is concluded that Raman spectroscopy is a good tool for quantitative characterization of Mg-doped InN. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)