[en] Carbon related luminescence and lattice distortion in wurtzite GaN are studied. C atoms are intentionally doped into GaN by ion implantation method with energies of 200 or 400 keV and a fluence of 1 x 10¹⁵ cm² and by a gas phase doping at 1273 K for 3 h under C₂H₆-gas flow. Lattice displacement of Ga atoms from <0 0 0 1> row in as-implanted samples is estimated to be of the magnitude of 0.013-0.014 nm by Rutherford backscattering (RBS)/channeling, while that in the gas phase doped sample is 0.008 nm, which is comparable to that of the unimplanted samples. The distortion in the implanted sample is not completely recovered. The Raman scattering intensity of E₂ phonon mode for the 200 keV is larger than that of the 400 keV, while that in the gas phase doping does not vary, supporting the RBS data. In all the doping methods, a prominent photoluminescence peak is observed at 3.293 eV with a small accompanied hump around 3.265 eV. These emissions are attributed to a band to C-acceptor and C donor-acceptor pair transitions, respectively, which suggests that binding energies of carbon acceptor and donor are ∼203 and ∼30 meV, respectively

[en] Substitution and electrical activation of carbon in ¹²C⁺- and ¹²C⁺+³¹P⁺-implanted InP were studied for various annealing stages (773-923 K for 20 min). ¹²C⁺ was implanted into semi-insulating InP at a range of ∼3.0 μm with a total dose of 3x10¹⁴ cm^-2. The co-implantation of ¹²C⁺ and ³¹P⁺ was performed at a range of ∼2.0 μm with an individual dose of 3x10¹⁴ cm^-2. Rutherford back scattering, X-ray diffraction and Raman spectroscopy measurements showed the improvement of the crystallinity in the InP matrix by the annealing, indicating the disappearance of the introduced vacancy-interstitial pairs. Those were introduced during ion irradiation. All the annealed samples showed the n-type conduction by a van der Pauw method. The electric activation rate in the ¹²C⁺ implanted samples reached to 4.5% for those annealed at 923 K. For the co-implanted samples, the rate was slightly improved (∼7.3%). Nuclear reaction analyses for the ¹²C⁺-implanted samples using a ¹²C(d,p)¹³C reaction showed a tendency that carbon is easily incorporated into the interstitial lattice sites

[en] Short communication

[en] Published in summary form only

[en] Band gap of LiInO₂ is studied by a photoacoustic spectroscopy (PAS). LiInO₂ is a candidate material for solar neutrino detection due to an inverse β^--decay of ¹¹⁵In. LiInO₂ samples synthesized by a sol gel method are confirmed to be the single phase of LiInO₂ (the lattice constant: a=4.3141 Aa and c=9.3549 Aa, the space group: I4₁/amd) by a powder X-ray diffraction and their crystallinity is confirmed by a Raman scattering spectroscopy. The PAS spectra of LiInO₂ show a knee at around 4.3 eV, suggesting the optical absorption related to the band gap of LiInO₂. The band gap value of 4.3 eV evaluated by PAS is close to the optical band gap (4.4 eV) observed by an optical absorption method. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] The energy level of Ge in Ge-ion implanted ZnO single crystals is studied by Hall-effect and photoluminescence (PL) methods. The variations in resistivity from ∼10³ Ωcm for un-implanted samples to ∼10⁻² Ωcm for as-implanted ones are observed. The resistivity is further decreased to ∼10⁻³ Ωcm by annealing. The origins of the low resistivity are attributed to both the zinc interstitial (Zn_i) related defects and the electrical activated Ge donor. An activation energy of Ge donors estimated from the temperature dependence of carrier concentration is 102 meV. In PL studies, the new peak at 372 nm (3.33 eV) related to the Ge donor is observed in 1000 °C annealed samples

[en] Persistent Photoconductivity (PPC) in hydorogen-ion implanted (001) oriented KNbO₃ bulk single crystals (perovskite structure at room temperature; ferroelectric with a band gap of 3.16 eV) is studied in air at room temperature to prevent the crystallinity degradation caused by the phase transition. Hydrogen is implanted into KNbO₃ bulk single crystals using the energy (the peak ion fluence) of 500 keV (5.0 × 10¹⁵ cm^-2). The resistivity varies from ∼10⁸ Ω/□ for an un-implanted KNbO₃ sample to 2.3 × 10⁵ Ω/□ for as-implanted one. suggesting the presence of donors consisting of hydrogen interstitial and oxygen vacancy. The PPC is clearly observed with ultraviolet and blue LEDs illumination rather than green and infrared, suggesting the release of electrons from the metastable conductive state below the conduction band relating to the charge states of the oxygen vacancy as observed in electron irradiated ZnO. (paper)

[en] Persistent photoconductivity (PPC) in 30-MeV electron irradiated ZnO single crystals is studied by excitation using light emitting diodes (LEDs) with various wavelengths. The decay transient of the photoconductivity shows relaxation times in the range of a few ten days for the illumination at 90 K and a few hours at room temperature. An electron paramagnetic resonance (EPR) signal with g-value = 2.005 appears after illumination of blue LED, suggesting the transfer from the artificially introduced oxygen vacancy of 2+ charge state to the metastable + charge state. Once generated, the metastable state does not immediately decay into the 2+ charge state because of energetic barriers of ∼190 meV, supporting the mechanism of PPC proposed by Van de Walle.

[en] The transmuted-C related luminescence and net carrier concentration are studied by combining photoluminescence, liquid scintillation, and Raman scattering. GaN single crystal films grown by metalorganic-vapor-phase epitaxy are irradiated with fast and thermal neutrons at fluxes of 3.9 × 10¹³ cm⁻²s⁻¹ and 8.15 × 10¹³ cm⁻²s⁻¹, respectively. Irradiation time is 48 hours. The calculated ⁷²Ge and ¹⁴C concentrations are 1.24 × 10¹⁸ cm⁻³ and 1.13 × 10¹⁸ cm⁻³, respectively. The transmuted ¹⁴C is detected by the liquid scintillation method to survey β-rays emitted in the process of ¹⁴C decays from ¹⁴N. Tritium (³H) is also emitted by a (n,t) reaction of ¹⁴N due to the neutron irradiation above 4.5 MeV. Photoluminescence relating to C, DX-like center of Ge and yellow luminescence band are observed in 1000 °C annealed NTD-GaN. The free electron concentration estimated from Raman scattering is 4.97 × 10¹⁷ cm⁻³. This value is lower than that from the transmuted Ge concentration, suggesting the compensation due to the transmuted ¹⁴C acceptors

[en] The origins of low resistivity in Al ion-implanted ZnO bulk single crystals are studied by combining Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), photoluminescence (PL), and Van der Pauw methods. The Al-ion implantation (peak concentration: 2.6 x 10²⁰cm^-3) into ZnO is performed using a multiple-step energy. The resistivity decreases from ∼10⁴Ω cm for un-implanted ZnO to 1.4 x 10^-1Ω cm for as-implanted, and reaches 6.0 x 10^-4Ω cm for samples annealed at 1000 deg. C. RBS and NRA measurements for as-implanted ZnO suggest the existence of the lattice displacement of Zn (Zn_i) and O (O_i), respectively. After annealing at 1000 deg. C, the Zn_i related defects remain and the O_i related defects disappear. The origin of the low resistivity in the as-implanted sample is attributed to the Zn_i (∼30 meV [Look et al., Phys. Rev. Lett. 82, 2552 (1999)]). In contrast, the origin of the low resistivity in the sample annealed at 1000 deg. C is assigned to both of the Zn_i related defects and the electrically activated Al donor. A new PL emission appears at around 3.32 eV after annealing at 1000 deg. C, suggesting electrically activated Al donors.