Search

Evolution of the microwave-probed photoconductivity transients and of the proton induced luminescence has simultaneously been examined in polycrystalline CdS layers evaporated in vacuum during exposure to a 1.6MeV proton beam. The decrease of the intensity of luminescence peaked at 510 and 709 nm wavelengths and of values of the effective carrier lifetime has been correlated in dependence of proton irradiation fluence. The defect introduction rate has been evaluated by the comparative analysis of the laser and proton beam induced luminescence. The difference of a carrier pair generation mechanism inherent for light and for a proton beam has been revealed. [ABSTRACT FROM AUTHOR]

The ESR spectrometry, based on alanine dosimeters, is a standard tool for dosimetry of different type ionizing radiations. The calibrated dosimeters and ESR readers operate rather reliably in the dose range up to 200 kGy. In this study, the ESR spectrometry of stable free radicals in alanine, induced by penetrative X- and ?-rays as well as neutron and stopped proton irradiations covering the dose range from a few Gy to a few MGy, has been performed in order to create the generalized calibration function for the wide range dosimetry. The simulations based on the cumulative generation of ESR active stable radicals R1, R2 and R3 enabled us to derive the generalized calibration model ascribed to the irradiation fluence from 1010 to 2 × 1016 particle/cm² normalized using 1 MeV neutron equivalent. [ABSTRACT FROM AUTHOR]

Evolution of the non-radiative and radiative recombination in GaN and CdS 2.5–20 μm thick layers has been examined by the in situ measurements of the 1.6 MeV proton induced luminescence and laser excited photoconductivity characteristics. The introduction rate of radiation defects has been evaluated by the comparative analysis of the laser and proton beam induced luminescence for the examined GaN and CdS layers. [ABSTRACT FROM AUTHOR]

Instrument and methods for the remote and in situ control of carrier recombination parameters during irradiation by protons of energy in the range of 3–8 MeV are presented. Direct techniques for measurements and separation of carrier recombination and trapping/generation characteristics based on the analysis of microwave probed photoconductivity transients during exposure on protons of different energies and irradiations at different temperatures are described. Simultaneously, a spectroscopy of activation energy of dominant traps has been performed before and just after irradiation by temperature scans of variation in the recombination parameters. [ABSTRACT FROM AUTHOR]

Abstract: Combined analysis of the carrier recombination and generation lifetime as well as reverse recovery durations (τRR ), dependent on proton irradiation fluence in the range of 7×1012−7×1014 p/cm2, has been performed in FZ silicon PIN diodes and wafer structures. A δ-layer and triangle profiles of radiation induced defects were formed by varying energy of protons in the range 2–3MeV. Carrier decay constituents and values of recombination lifetime have been evaluated by employing a microwave probed photoconductivity transient technique, while deep levels spectra ascribed to generation lifetime variations have been examined by exploiting capacitance deep-level transient (DLTS) spectroscopy. Recombination lifetime decreases from several μs to few ns, while DLTS spectra show an increase in the amplitude of a DLTS peak at 170K with irradiation fluence. Transforms of DLTS spectra and a decrease in density of the majority carrier traps have been revealed after 24h isochronal anneals in the range of temperatures of 80–420°C. Inhomogeneous depth distribution of recombination lifetime in proton irradiated samples has been revealed from the cross-sectional scans of the excess carrier lifetime measured by MW-PC technique and compared for δ-layer and triangle profiles of radiation induced defects. After isochronal anneals, the τRR changes its behaviour as a function of irradiation fluence. [Copyright &y& Elsevier]

CERN RD39 Collaboration develops radiation-hard cryogenic silicon detectors. Recently, we have demonstrated improved radiation hardness in novel Current Injected Detectors (CID). For detector characterization, we have applied cryogenic Transient Current Technique (C-TCT). In beam tests, heavily irradiated CID detector showed capability for particle detection. Our results show that the CID detectors are operational at the temperature -50° C after the fluence of 1 × 1016 1 MeV neutron equivalent/cm2. [ABSTRACT FROM AUTHOR]

Abstract: The effect of native and radiation induced defects on the photoconductivity transients and photoluminescence spectra have been examined in GaN epitaxial layers of 2.5 and 12μm thickness grown on bulk n-GaN/sapphire substrates by metal-organic chemical vapor deposition (MOCVD). For comparison, free-standing GaN as-grown samples of 500μm thickness, fabricated by hydride vapor phase epitaxy (HVPE), were investigated. Manifestation of defects induced by 10-keV X-ray irradiation with the dose of 600Mrad and 100-keV neutrons with the fluences of and 1016 cm−2 as well as of 24GeV/c protons with fluence 1016 cm−2 have been revealed through contact photoconductivity and microwave absorption transients. The amplitude of the initial photoconductivity decay is significantly reduced by the native and radiation defects density. Synchronous decrease of the steady-state PL intensity of yellow, blue and ultraviolet bands peaked at 2.18, 2.85, and 3.42eV, respectively, with density of radiation-induced defects is observed. The decrease of the PL intensity is accompanied by an increase of asymptotic decay lifetime in the photoconductivity transients, which is due to excess-carrier multi-trapping. The decay fits the stretched exponent approximation exp[] with the different factors in as-grown material () and irradiated samples (). The fracton dimension ds of disordered structure changes from 4.7 to 0.86 for as-grown and irradiated material, respectively, and it implies the percolative carrier motion on an infinite cluster of dislocations net in the as-grown material and cluster fragmentation into finite fractons after irradiations. [Copyright &y& Elsevier]

Abstract: Carrier lifetime variations dependent on proton irradiation at fluences in the range from 5×1012 to 1015 cm−2 and γ-ray doses ranging from 50 to 400Mrad were investigated in high-resistivity oxygenated silicon wafers and pad detectors. Fast recombination and slow trapping constituents within recombination transients have been distinguished by combining analyses of excess carrier decays dependent on excitation intensity and temperature, measured using the technique of microwave absorption by free carriers. Difference in defect formation rate and type of defects in the ranges of moderate and highest proton irradiation fluences as well as between γ-ray- and proton-irradiated material have been revealed from the inverse lifetime dependence on irradiation fluence and on temperature. The activation factors of the capture centers have been evaluated from carrier lifetime variations in the range of low and elevated temperatures. [Copyright &y& Elsevier]

Abstract: The influence of radiation defects on photoconductivity transients and photoluminescence (PL) spectra have been examined in semi-insulating GaN epitaxial layers grown on bulk n-GaN/sapphire substrates. Defects induced by 10-keV X-ray irradiation with a dose of 600Mrad and 100-keV neutrons with fluences of 5×1014 and 1016 cm−2 have been revealed through contact photoconductivity and microwave absorption transients. The amplitude of the initial photoconductivity decay is significantly reduced by the radiation defect density. A simultaneous decrease with radiation-induced defect density is also observed in the steady-state PL intensity of yellow, blue and ultraviolet bands peaked at 2.18, 2.85, and 3.42eV, respectively. The decrease of the PL intensity is accompanied by an increase of asymptotic decay lifetime, which is due to excess carrier multi-trapping. The decay can be described by the stretched exponential approximation exp[] with different values of in as-grown material () and irradiated samples (). The value of the fracton dimension d s of the disordered structure, evaluated as , changes from 4.7 to 0.86 for as-grown and irradiated material, respectively, implying percolative carrier motion on an infinite cluster of dislocations net in the as-grown material and cluster fragmentation into finite fractons after irradiation. [Copyright &y& Elsevier]

Abstract: Carrier lifetime variations dependent on proton irradiation with fluences in the range from 5×1012 to 1015 cm−2 were investigated in high resistivity oxygenated silicon wafers and pad detectors. The fast recombination and slow trapping constituents within recombination transients have been distinguished by combining analyses of the excess carrier decay dependence on the excitation intensity, bias illumination and temperature, measured using the technique of microwave absorption by free carriers. Differences in the rate of formation and type of defects in the ranges of moderate and highest proton irradiation fluences have been revealed from the inverse lifetime dependence on irradiation fluence. The activation factors of the capture centres have been evaluated from carrier lifetime variations in the range of low and elevated temperatures. [Copyright &y& Elsevier]

Abstract: Comparative study of the carrier recombination and generation lifetime as well as reverse recovery durations (RR), dependent on 2MeV proton irradiation fluences in the range of 7×1012−7×1014 p/cm2 and on anneal regimes, has been performed in FZ silicon pin diodes and wafer structures. Recombination lifetimes from several μs to few ns have been measured by employing a microwave probed photoconductivity transient technique (MW-PC), while deep levels spectra, ascribed to emission lifetime variations, have been examined by exploiting capacitance deep level transient spectroscopy (C-DLTS). Variations of the six DLTS peaks are examined under isochronal anneals in the range of temperatures of 80–320°C. [Copyright &y& Elsevier]

Abstract: Semiconductor tracking detectors at experiments such as ATLAS and LHCb at the CERN Large Hadron Collider (LHC) will be subjected to intense levels of radiation. The proposed machine upgrade, the Super-LHC (SLHC), to 10 times the initial luminosity of the LHC will require detectors that are ultra-radiation hard. Much of the current research into finding a detector that will meet the requirements of the SLHC has focused on using silicon substrates with enhanced levels of oxygen, for example Czochralski silicon and diffusion oxygenated float zone silicon, and into novel detector structures such as 3D devices. Another avenue currently being investigated is the use of wide band gap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN). Both SiC and GaN should be intrinsically more radiation hard than silicon. Pad and guard ring structures were fabricated on three epitaxial GaN wafers. The epitaxial GaN thickness was either 2.5 or and the fabricated detectors were irradiated to various fluences with protons and 1MeV neutrons. Detectors were characterised pre- and post-irradiation by performing current–voltage (–) and charge collection efficiency (CCE) measurements. Devices fabricated on epitaxial GaN irradiated to fluences of and show maximum CCE values of 26% and 20%, respectively, compared to a maximum CCE of 53% of the unirradiated device. [Copyright &y& Elsevier]

The recovery of the charge collection efficiency (CCE) at low temperatures, the so-called ”Lazarus effect”, was studied in Si detectors irradiated by fast reactor neutrons, by protons of medium and high energy, by pions and by gamma-rays. The experimental results show that the Lazarus effect is observed: (a) after all types of irradiation; (b) before and after space charge sign inversion; (c) only in detectors that are biased at voltages resulting in partial depletion at room temperature. The experimental temperature dependence of the CCE for proton-irradiated detectors shows non-monotonic behaviour with a maximum at a temperature defined as the CCE recovery temperature. The model of the effect for proton-irradiated detectors agrees well with that developed earlier for detectors irradiated by neutrons. The same midgap acceptor-type and donor-type levels are responsible for the Lazarus effect in detectors irradiated by neutrons and by protons. A new, abnormal “zigzag”-shaped temperature dependence of the CCE was observed for detectors irradiated by all particles (neutrons, protons and pions) and by an ultra-high dose of γ-rays, when operating at low bias voltages. This effect is explained in the framework of the double-peak electric field distribution model for heavily irradiated detectors. The redistribution of the space charge region depth between the depleted regions adjacent to p+ and n+ contacts is responsible for the “zigzag”- shaped curves. It is shown that the CCE recovery temperature increases with reverse bias in all detectors, regardless of the type of radiation. [Copyright &y& Elsevier]