Uniform and vertically aligned nanotube arrays of titanium oxynitride functionalized with iridium nanoparticles (Ir/TiON-NTs) were fabricated for the solar driven-water splitting.

Optically-detected magnetic resonance (ODMR) and positron annihilation spectroscopy (PAS) experiments have been employed to study magnesium-doped GaN layers grown by metal-organic vapor phase epitaxy. As the Mg doping level is changed, the combined experiments reveal a strong correlation between the vacancy concentrations and the intensity of the red photoluminescence band at 1.8 eV. The analysis provides strong evidence that the emission is due to recombination in which electrons both from effective mass donors and from deeper donors recombine with deep centers, the deep centers being vacancy-related defects.Deep defects play a key role in the performance limits and aging effects of GaN-based light-emitting devices. They also lead to photoluminescence (PL) at energies well below the band-gap. For example, PL and opticallydetected magnetic resonance (ODMR) studies [1,2,3,4] have suggested that deep defects are responsible for the red (1.8 eV) luminescence band which is often observed in Mg-doped GaN and that the band is due to recombination emission in which vacancy-dopant complexes are involved [1,2]. However, this proposal was mainly based on indirect evidence and on previous experience of II -VI compounds, and further experimental confirmation is therefore needed. The present study involved the use of both ODMR and positron annihilation spectroscopy (PAS) on the same set of samples covering a range of Mg doping levels and we have established a correlation between the ODMR spectra (obtained by monitoring the red PL) and the PAS results.ODMR is well established as a means of investigating centers involved in recombination processes in semiconductors [5,6]. For a detailed description of the technique and our ODMR system, see Ref. [7]. The ODMR was carried out at 14 GHz with the specimen at 2K. The PL was excited with a UV argon-ion laser (363.8/351.1 nm). The microwaves were chopped at 605 Hz and changes in the PL intensity caused by magnetic resonance were monitored at this frequency as the magnetic field was slowly swept. PAS with a slow positron beam is an effective tool for the investigation of open volume defects such as neutral or negatively charged vacancies in semiconductor films. When positrons annihilate electrons in semiconductors the resulting gamma ray energy spectrum, peaked at 511 keV, is Doppler-broadened (since the electrons have a range of momenta). The annihilation linewidth is characterized by quantities S (W ), defined as the central (wing) fraction of the line. The value of S (W ) is characteristic of the material under study, but * Electronic address: d.wolverson@bath.ac.uk is generally higher (lower) when vacancies are present [8]. Measurements of S (W ) can thus be used to monitor vacancy concentrations. In the present work, singledetector Doppler-broadening PAS was performed using a magnetic transport positron beam system [9]. Positrons were implanted into the layers at energies in the range 0.1 -30 keV, corresponding to mean depths up to 1.5 nm.Details of the growth of the GaN:Mg sampl...

Shallow fluorine-vacancy ͑FV͒ complexes in Si have been directly observed using variable-energy positron annihilation spectroscopy and secondary ion mass spectrometry. The FV complexes, introduced to combat the deactivation and transient-enhanced diffusion of ultrashallow boron, were observed in preamorphized Si wafers implanted with 0.5 keV B and 10 keV F ions at a dose of 10 15 cm −2 , and then annealed isothermally at 800°C for times ranging from 1 to 2700 s. The results are in agreement with a model which predicts that the complexes are of the form F 3n V n , with n most probably being 1 and/or 2. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2335594͔Interest in the beneficial consequences of implanting F ions in Si has grown in recent years as defect engineering has been developed to meet the continuing challenges of device miniaturization. The application of particular interest here concerns ultrashallow B implantation into preamorphized Si regrown via solid-phase epitaxy ͑SPE͒; efficient activation of the B while limiting its diffusion is the key to the formation of ultrashallow junctions. Recent work by Cowern et al. 1 showed that F in B-implanted Si can form clusters that trap interstitals ͑I͒ released from the band of end-of-range ͑EOR͒ defects, which in turn both retard the transient enhanced diffusion of B implants and significantly decrease their deactivation. Kham et al. 2 linked F found at half the projected ion range to the formation of clusters of F with vacancies ͑V͒ in this region. Other studies conclude that FV or FI complexes suppress B diffusion by reducing I emission from extended I defects generated by implantation. 3,4 Variable-energy positron annihilation spectroscopy ͑VE-PAS͒ is used here to probe the nature of the complexes formed by the implanted F ions. The technique has been used to identify FV complexes in thermally treated F-implanted Si. 5,6 VEPAS measures the Doppler broadening of the 511 keV ␥-ray annihilation line, whose extent is determined by the average momentum of the electrons at the annihilation site. The broadening is characterized by the line-shape parameter S, defined as the central fraction of the 511 keV line. S for a chosen experimental setup has a characteristic value for each annihilation site, for example, for pure bulk Si or for each specific vacancy-type defect, the latter being strong positron traps. The mean depth z of positrons implanted with energy E ͑keV͒ is determined from the relation z = 17.2 E 1.6 nm. Secondary ion mass spectrometry ͑SIMS͒ measurements were performed to determine atomic profiles.Samples used in this study were n-type ͗100͘ Cz Si wafers with a resistivity of 10-20 ⍀ cm. All wafers were first preamorphized with 30 keV, 10 15 cm −2 Ge ions, and implanted with 0.5 keV B ions at 10 15 cm −2 . Half of the samples were additionally implanted with F ions at 10 keV and 10 15 cm −2 , placing the F ions between the B implants and the amorphous-crystalline interface. After restoring the amorphous layer to crystallinity via SPE regrowth ...

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