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Objective: The purpose of this study was to analyse changes in regional cerebral blood flow (rCBF) in Parkinson's disease (PD) without dementia. Methods: Twenty eight non-demented patients with PD and [...]

Different carrier concentrations have been measured in the Raman spectra of n-type gallium nitride (GaN), and an increase in carrier concentration results in the LO phonon band shifting and broadening toward the high frequency side. Carrier concentrations of GaN can be determined from Hall measurements or by the line-shape fitting of the coupled modes. The different carrier concentrations suggest that deformation potential and electro-optic mechanisms are the dominant scattering mechanisms in GaN.

Thermal quenching of the defect-related photoluminescence (PL) has been widely used to determine the fundamental properties of point defects in GaN such as the activation energy (Et) and capture cross section. However, in the present work, we have shown using drift-diffusion modeling and experimental analysis that the thermal quenching of defect-related PL from GaN does not only depend of the defect parameters but also is strongly governed by the carrier drift and diffusion in the depletion region. In particular, we have found that these processes significantly influence the slope of PL thermal quenching and temperature T0 at which the quenching begins. As a result, Et obtained from the Arrhenius plot of the defect-related PL intensity in GaN provides the correct values of the defect activation energy only in the case of low surface state density (cm−2eV−1) corresponding to the weak surface band bending. However, in the case of high D0 giving rise to the significant surface band bending, the Et value should be cautiously interpreted because it may not correspond entirely to the real defect activation energy due to the drift-diffusion process. Finally, we have shown that our finding can explain in a coherent manner various anomalous behaviors of PL thermal quenching reported in the literature, such as tunable, abrupt or sample dependent thermal quenching. We believe that our findings can be very interesting for nitride growth technology community and optoelectronic device applications. [ABSTRACT FROM AUTHOR]

The plasma etching damage in p-type GaN has been characterized. From current-voltage and capacitance-voltage characteristics of Schottky diodes, it was revealed that inductively coupled plasma (ICP) etching causes an increase in series resistance of the Schottky diodes and compensation of acceptors in p-type GaN. We investigated deep levels near the valence band of p-type GaN using current deep level transient spectroscopy (DLTS), and no deep level originating from the ICP etching damage was observed. On the other hand, by capacitance DLTS measurements for n-type GaN, we observed an increase in concentration of a donor-type defect with an activation energy of 0.25 eV after the ICP etching. The origin of this defect would be due to nitrogen vacancies. We also observed this defect by photocapacitance measurements for ICP-etched p-type GaN. For both n- and p-type GaN, we found that the low bias power ICP etching is effective to reduce the concentration of this defect introduced by the high bias power ICP etching. [ABSTRACT FROM AUTHOR]

Defects in ion-implanted GaN and their annealing properties were studied by using monoenergetic positron beams. Doppler broadening spectra of the annihilation radiation and the positron lifetimes were measured for Si+, O+, and Be+-implanted GaN grown by the metal-organic chemical vapor deposition technique. First-principles calculations were also used to identify defect species introduced by the implantation. For as-implanted samples, the major defect species was identified as Ga vacancies and/or divacancies. An agglomeration of defects starts after annealing at 400 °C, and the defect profile shifted toward the surface with the open volumes of the defects increasing. The annealing properties of defects were found to depend on the ion species, and they are discussed here in terms of defect concentrations and interactions between impurities and defects. [ABSTRACT FROM AUTHOR]

Electrical activation studies of Si-implanted GaN layers on sapphire were made as a function of annealing temperature (1100–1400 °C). For an ion dose of 1.0×1014 cm-2, the optimum annealing temperature was 1400 °C, exhibiting a nearly 100% electrical activation efficiency and a low sheet resistance of ∼450 Ω/square at room temperature. From variable temperature Hall-effect measurements, Si-implanted GaN films annealed below 1200 °C displayed deep ionization levels of ∼280 meV, whereas samples annealed above 1300 °C had shallow ones of ∼11 meV. For lateral Schottky diodes fabricated on Si-implanted GaN layers annealed below 1200 °C, capacitance frequency and thermal admittance measurements showed a typical dispersion effect characteristic of a single deep donor with an activation energy of ∼133 meV. These results illustrate that deep donor levels created by the Si implantation in GaN layers apparently annihilate and transit to shallow levels produced by the Si ion substitution for Ga in the GaN lattice (SiGa) by annealing at temperature greater than ∼1300 °C at these doses. [ABSTRACT FROM AUTHOR]

Details a study which investigated thermal stress in gallium nitride epitaxial layers with different thickness grown on sapphire substrates. Experimental procedures; Findings of Raman scattering measurement; Conclusion.

Analyzes YBa[sub2]Cu[sub3]O[subx] thin films with x=6-7 by oxygen in-diffusion following laser deposition. Background on the experimental synthesis of the films through laser deposition without post-annealing; Assessment of the possible relation between oxygen content and oxygen pressure; Evaluation of findings after the laser depositions.