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The depletion width and full depletion condition are essential parameters in the search for radiation tolerant detector design and operational regimes. In this work, results of measurements of barrier capacitance by combining a transient technique for barrier evaluation by linearly increasing voltage (BELIV), with temperature dependent capacitance-voltage and current-voltage characteristics of neutron irradiated Si pin detectors are discussed. It is shown that the generation current, caused by a high density of radiation induced traps, distorts the capacitance measurements in heavily irradiated devices. There is no space charge sign inversion effect, however, and heavily irradiated detectors become fully depleted in equilibrium. [ABSTRACT FROM AUTHOR]

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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]

The proposed upgrade of the CERN Large Hadron Collider to ten times brighter luminosity poses severe challenges to semiconductor detector within the CERN experiments. We in- vestigate a silicon "3-D" detector design for these conditions and semiconductors alternative to silicon, namely silicon carbide and gallium nitride. Charge collection measurements suggest some degree of additional radiation tolerance over conventional detector geometry and materials. [ABSTRACT FROM AUTHOR]

The in situ examination of barrier capacitance charging, of generation and drift currents, and of carrier lifetime in Si structures during 25 MeV neutrons irradiation has been implemented to correlate radiation induced changes in carrier recombination, thermal release, and drift characteristics and to clarify their impact on detector performance. It has been shown that microwave probed photo-conductivity technique implemented in contact-less and distant manner can be a powerful tool for examination in wide dynamic range of carrier lifetime modified by radiation defects and for rather precise prediction of detector performance. [ABSTRACT FROM AUTHOR]

Effect of radiation defects on the photoconductivity transients and photoluminescence (PL) spectra have been examined in semi-insulating GaN epitaxial layers grown on bulk n-GaN/sapphire substrates. Manifestation of defects induced by 10 keV x-ray irradiation with the dose of 600 Mrad and 100 keV neutrons with the fluence of 5×1014 cm-2 have been revealed through steady-state and pulsed PL as well as through contact photoconductivity and microwave absorption transients. Synchronous decrease of the PL intensity of yellow, blue, and ultraviolet bands peaked at 2.19, 2.85, and 3.42 eV, respectively, with density of radiation-induced defects is observed. 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 fits the stretched exponent approximation exp[-(t/τ)α] with the different factors α in as-grown material (α≈0.7) and irradiated samples (α≈0.3). [ABSTRACT FROM AUTHOR]

We pursue scribe–cleave–passivate (SCP) technology for making “slim edge” sensors. The goal is to reduce the inactive region at the periphery of the devices while maintaining their performance. In this paper we report on two aspects of the current efforts. The first one involves fabrication options for mass production. We describe the automated cleaving tests and a simplified version of SCP post-processing of n-type devices. Another aspect is the radiation resistance of the passivation. We report on the radiation tests of n- and p-type devices with protons and neutrons. [ABSTRACT FROM AUTHOR]

Abstract: Radiation hardness up to 1016 n eq/cm2 is required in the future HEP experiments for most inner detectors. However, 1016 n eq/cm2 fluence is well beyond the radiation tolerance of even the most advanced semiconductor detectors fabricated by commonly adopted technologies: the carrier trapping will limit the charge collection depth to an effective range of 20–30μm regardless of depletion depth. Significant improvement of the radiation hardness of silicon sensors has been taken place within RD39. Fortunately the cryogenic tool we have been using provides us a convenient way to solve the detector charge collection efficiency (CCE) problem at SLHC radiation level (1016 n eq/cm2). There are two key approaches in our efforts: (1) use of the charge/current injection to manipulate the detector internal electric field in such a way that it can be depleted at a modest bias voltage at cryogenic temperature range (⩽230K); and (2) freezing out of the trapping centers that affects the CCE at cryogenic temperatures lower than that of the LN2 temperature. In our first approach, we have developed the advanced radiation hard detectors using charge or current injection, the current injected diodes (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge, yielding a nearly uniform electric field in the detector, independent of the radiation fluence. In our second approach, we have developed models of radiation-induced trapping levels and the physics of their freezing out at cryogenic temperatures. In this approach, we intend to study the trapping effect at temperatures below LN2 temperature. A freeze-out of trapping can certainly help in the development of ultra-radiation hard Si detectors for SLHC. A detector CCE measurement system using ultra-fast picosecond laser with a He cryostat has been built at CERN. This system can be used to find out the practical cryogenic temperature range that can be used to freeze out the radiation-induced trapping levels, and it is ready for measurements on extremely heavily irradiated silicon detectors. Initial data from this system will be presented. [Copyright &y& Elsevier]

Abstract: In this work two wide bandgap materials, silicon carbide (SiC) and gallium nitride (GaN), were investigated for their performance in harsh radiation environments. Schottky devices were fabricated on vanadium doped SiC (V-SiC), Okmetic semi insulating (SI) non-vanadium doped SiC, SI GaN grown by MOCVD (metal organic chemical vapour deposition) and bulk GaN. Completed devices were electrically characterised and the CCE (charge collection efficiency) calculated from pulse height spectra of 241Am particles. SI GaN samples were irradiated with estimated neutron fluences of up to (Ljubljana), proton fluences of (CERN), and a dose of 600Mrad of 10keV X-rays (ICSTM, London). V-SiC samples were irradiated up to using 300MeV/c pions (PSI). Electrical characterisation and CCE calculations were repeated after irradiation to observe changes in properties caused by radiation induced damage. [Copyright &y& Elsevier]