R. Irsigler

University of Freiburg, Freiburg, Baden-Württemberg, Germany

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Publications (27)21.91 Total impact

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    ABSTRACT: Measurements of the performance of a Resistive Gate CCD will be shown and discussed. A short description of structure and layout will be followed by X-ray spectra, linearity, noise, SNR and energy resolution. A charge transfer efficiency of calculated with the classical method of 0.99958±0.00002 was reached. Simulation and layout of a newly designed X-ray Schottky CCD will be presented.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2001; 460(1):72-75. · 1.14 Impact Factor
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    ABSTRACT: We report on gain and offset corrections for GaAs X-ray pixel detectors, which were hybridised to silicon CMOS readout integrated circuits (ROICs). The whole detector array contains 320×240 square-shaped pixels with a pitch of 38μm. The GaAs pixel detectors are based on semi-insulating and VPE grown substrates. The ROIC operates in the charge integration mode and provides snapshot as well as real time video images. Previously we have reported that the image quality of semi-insulating GaAs pixel detectors suffer from local variations in X-ray sensitivity. We have now developed a method to compensate for the sensitivity variations by applying suitable offset and gain corrections. The improvement in image quality is demonstrated in the measured signal-to-noise ratio of flood exposure images.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2001; 460(1):67-71. · 1.14 Impact Factor
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    ABSTRACT: We present room temperature measurements of inhomogeneities and instabilities in a GaAs pixel detector array at high bias voltage. The evolution of the inhomogeneity structure and its change due to increase of bias voltage was investigated. The dark current image was analyzed. It is proposed that a cellular structure of higher and lower conductivity regions is responsible for the inhomogeneities and their spatial and temporal instability. The electrical inhomogeneity in LEC SI- GaAs and its dependence on electric field was qualitatively investigated by using a hybridized GaAs pixel detector and a model of the influence of crystal inhomogeneity on the measured parameters of the detector array is proposed.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2001; · 1.14 Impact Factor
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    ABSTRACT: 320×240 pixels GaAs Schottky barrier detector arrays were fabricated, hybridized to silicon readout circuits, and subsequently evaluated. The detector chip was based on semi-insulating LEC GaAs material. The square shaped pixel detector elements were of the Schottky barrier type and had a pitch of m. The GaAs wafers were thinned down prior to the fabrication of the ohmic back contact. After dicing, the chips were indium bump, flip-chip bonded to CMOS readout circuits based on charge integration, and finally evaluated. A bias voltage between 50 and 100V was sufficient to operate the detector. Results on I–V characteristics, noise behaviour and response to X-ray radiation are presented. Images of various objects and slit patterns were acquired by using a standard dental imaging X-ray source. The work done was a part of the XIMAGE project financed by the European Community (Brite-Euram).
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 09/1999; · 1.14 Impact Factor
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    ABSTRACT: Digital systems for dental X-ray imaging are rapidly replacing conventional film techniques. The major advantages of digital systems are reduced X-ray doses due to increased sensitivity, time savings since no development is needed and reduced use of chemicals for film development. Most of the currently available digital systems are based on a silicon CCD coated with a scintillating material. In this paper we present some of the research going on in order to develop new X-ray imaging sensors with improved sensitivity.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 09/1999; · 1.14 Impact Factor
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    ABSTRACT: We present room temperature measurements on 200 μm thick GaAs pixel detectors, which were hybridized to silicon readout circuits. The whole detector array contains 320×240 square shaped pixel with a pitch of 38 μm and is based on semi-insulating liquid-encapsulated Czochralski (LEC) GaAs material. After fabricating and dicing, the detector chips were indium bump flip chip bonded to CMOS readout circuits based on charge integration and finally evaluated. This readout chip was originally designed for the readout of flip chip bonded infrared detectors, but appears to be suitable for X-ray applications as well. A bias voltage between 50 V and 100 V was sufficient to operate the detector at room temperature. The detector array did respond to X-ray radiation by an increase in current due to production of electron hole pairs by the ionization processes. Images of various objects and slit patterns were acquired by using a standard X-ray source for dental imaging. The new X-ray hybrid detector was analyzed with respect to its imaging properties. Due to the high absorption coefficient for X-rays in GaAs and the small pixel size, the sensor shows a high modulation transfer function up to the Nyquist frequency
    IEEE Transactions on Nuclear Science 07/1999; · 1.22 Impact Factor
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    ABSTRACT: Gallium Arsenide layers grown using low pressure Vapour-Phase Epitaxy (LP-VPE) were studied with CV, Hall-measurements and Photoluminescence. The results have been analysed for the general investigation of the influence of material properties on particle detector performance for X-ray applications. This p-type material exhibits a free carrier concentration of 1.3 × 1011 cm−3 at room temperature and was compensated by the presence of shallow donors and deep acceptors. Because of this, the detector performance was restricted by the space-charge density of the order of 1014 cm−3.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/1998; 410(1):92–95. · 1.14 Impact Factor
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    ABSTRACT: Full-size single-sided GaAs microstrip detectors with integrated coupling capacitors and bias resistors have been fabricated on 3″ substrate wafers. PECVD deposited SiO2 and layers were used to provide coupling capacitances of 32.5 and 61.6 pF/cm, respectively. The resistors are made of sputtered CERMET using simple lift of technique. The sheet resistivity of 78 kΩ/□ and the thermal coefficient of resistance of less than 4 × 10−3/°C satisfy the demands of small area biasing resistors, working on a wide temperature range.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/1998; · 1.14 Impact Factor
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    ABSTRACT: The bulk damage (namely the introduction rate of the arsenic antisite AsGa and its ionisation ratio, the Fermi-level position and resistivity) was determined as a function of the non-ionising energy loss (NIEL) of hadrons in semi-insulating (SI) GaAs. The study was performed using near-infrared (NIR) absorption and time dependent charge measurements (TDCM) on 23 GeV proton and 192 MeV pion irradiated Liquid Encapsulated Czochralski (LEC) grown GaAs. We have shown that the bulk damage scales linearly with the total NIEL up to a pion fluence of 5 × 1014particles/cm2. The EL2 introduction rate for the high energetic pions and protons were determined to be 92.7 ± 2.6 cm−1 and 68.1 ± 3.7 cm−1, respectively. A comparison of these values gives a hardness factor for the 192 MeV pions of 9.5 ± 1.4. In addition it was found that the variation of the Fermi-level and resistivity with radiation damage is a function of the initial resistivity of the SI GaAs before irradiation.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/1998; 134(1):53–60. · 1.19 Impact Factor
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    ABSTRACT: The bulk damage (namely the introduction rate of the arsenic antisite AsGa and its ionization ratio) was determined as a function of the non-ionizing energy loss (NIEL) of hadrons in semi-insulating GaAs. The study was performed using near-infrared absorption on 23 GeV proton and 192 MeV pion irradiated, Liquid Encapsulated Czochralski (LEC) grown GaAs. Together with the detector performance as a function of the radiation level, the results are used to explain the radiation damage in GaAs particle detectors.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/1998; 410(1):41-45. · 1.14 Impact Factor
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    ABSTRACT: The mobility lifetime product of holes and electrons under low electric field conditions was determined by alpha spectroscopy using SI-GaAs as a photo conductivity detector. The lifetime in high electric field (≥ 104V/cm) of electrons was investigated with Schottky diodes. Both results were analyzed as a function of substrate resistivity and trap concentrations. We identified the ionized arsenic antisite defect (EL2+) as the dominant electron trap in the high field region and determined the capture cross-section as being (8.0 ± 0.6) × 10−14 cm2.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/1998; 410(1):74-78. · 1.14 Impact Factor
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    ABSTRACT: Introduction Several aspects on the design of a semiconductor microstrip detectors has to be taken into account in order to get a good signal to noise ratio. First of all, the strip capacitance (the sum of the interstrip capacitances between neighbouring strips and the body capacitance of the strip) should be low because it determines the noise level of the readout electronics [1]. For short shaping times, there is almost no additional contribution due to the shot noise of the detector. This is still the case for the higher leakage currents of GaAs detectors (20 nA/mm 2 ) [2] compared to standard Si detectors (0.5 nA/mm 2 )[3]. Short shaping times have to be used because of the very high luminosity (10 34 cm Gamma2 s Gamma1 ) and high bunch crossing rate (40 MHz) at future high energy physics experiments like LHC [4]. 1 Correspon
    10/1997;
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    ABSTRACT: The effects of neutron and proton irradiation on the noise of detectors made from semi-insulating GaAs have been investigated. Using spectral noise density and equivalent noise-charge measurements, a decrease of shot noise with increasing particle fluence was found. A suppression of noise due to a space-charge effect is postulated and a correlation is shown with measured space-charge density.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/1997; · 1.14 Impact Factor
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    ABSTRACT: We present the results of charge collection measurements on liquid encapsulated Czochralski grown semi-insulating GaAs devices for alpha particles. Experimental evidence is given which demonstrates a drastic enhancement of charge collection efficiency after prolonged illumination with 1.086 μm below-gap light. The recovery of EL2 from metastable state to normal state can also be achieved by electric field at high bias voltage. The experimental result shows that the EL2 defect is practically the dominant trap for free charge carriers and together with other shallow defects responsible for the electric compensation in semi-insulating GaAs. The metastable transition of the EL2 defect is always simultaneously accompanied by the neutralization of a shallow acceptor. No change in the type of conductivity was found. © 1997 American Institute of Physics.
    Applied Physics Letters 05/1997; 70(20):2693-2695. · 3.52 Impact Factor
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    ABSTRACT: The radiation damage in 200 um thick Schottky diodes made on semi-insulating (SI) undoped GaAs Liquid Encapsulated Czochralski (LEC) bulk material with resistivities between 0.4 and 8.9*10E7 Ohm*cm were studied using alpha-spectroscopy, signal response to minimum ionising particles (MIP), I-V and CV-measurements. The results have been analysed to investigate the influence of the substrate resistivity on the detector performance after neutron and proton irradiation. The leakage current density, signal response to alpha-particles and MIPs show a strong dependence on the resistivity before and after irradiation. An observed decrease of the electron mean free drift length before and after irradiation with increasing substrate resistivity can be explained by a model involving the different ionisation ratios of defects, which are introduced by the irradiation. Comparison of the radiation damage due to neutrons and protons gives a hardness factor of 7+-0.9 for 24 GeV/c protons. The best detectors show a response to MIPs of 5250 e- at 200 V reverse bias after a irradiation level of 2*10E14 p/cm^2.
    05/1997;
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    ABSTRACT: To investigate the trapping and detrapping in SI-GaAs particle detectors we analyzed the signals caused by 5.48 MeV alpha particles with a charge sensitive preamplifier. From the bias and temperature dependence of these signals we determine the activation energies of two electron traps. Additional simulation and measurements of the lifetime as a function of resistivity have shown that the EL2+ is the dominant electron trap in semi-insulating GaAs. Comment: 13 pages, 6 Postscript figures, uses elsart.cls
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/1997; · 1.14 Impact Factor
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    ABSTRACT: We estimate the “hardness factors” and the equivalent 1 MeV neutron fluences of the hadron radiation level at the proposed GaAs forward tracker wheels in the ATLAS inner detector. On this basis, a prediction is given of the degradation of the GaAs particle detectors made on different substrates as a function of years of LHC operation.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/1997; · 1.14 Impact Factor
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    ABSTRACT: It is commonly observed, that semi-insulating GaAs detectors show leakage current densities between 1 and several 100nA/mm2. Also the breakdown voltage of those surface barrier detectors varies between 100 and 270 V for 200 μm thick devices. Moreover, the charge collection efficiency for alpha particles shows a strong correlation with the leakage current density of the detector. The presented measurements show, that the leakage current density is primarily determined by the substrate resistivity and not by the Schottky contact parameters.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/1997; 395(1):71-75. · 1.14 Impact Factor
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    ABSTRACT: Schottky diodes made of semi-insulating (SI) gallium arsenide and bulk material received from various manufactures were studied by using magnetic circular dichroism of absorption (MCDA), near-infrared absorption (NIR), CV- and Hall-measurements. The results have been analysed to investigate the influence of the EL2/EL2+-concentration to the detector properties. The MCDA measurements of these different materials showed a variation of the EL2+-concentration between 3.0 and 6.5 × 1015 cm−3. A likely dependence of the charge collection efficiency (CCE) for alpha particles on the EL2+-concentration was observed. Also an influence of the EL2+-concentration on the space charge density measured by CV and the leakage current density can be seen. No correlation between the room temperature mobility and the EL2+-concentration was found. We conclude that the EL2+-concentration and the position of the Fermi level have a influence on the detector performance.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 10/1996; 380(1):14-17. · 1.14 Impact Factor
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    ABSTRACT: GaAs Schottky diodes made by commercial undoped semi-insulating (SI) material have been shown to work well as radiation detectors. This material offers high radiation resistance together with high charge carrier mobility, good signal-to-noise ratio and a good detection efficiency for minimum ionizing particles. To optimise the detector performance of Schottky diodes made on SI-GaAs, the influence of the compensation on the formation of the space charge region and charge collection efficiency (CCE) for alpha particles was studied. A strong dependence of the CCE on the ionized state of the arsenic antisite defect As<sub>Ga</sub><sup>+</sup> and the resistivity determined from the Norde plot was observed. Also the influence of the compensation on the Schottky barrier height and space charge density can been seen
    Semiconducting and Semi-Insulating Materials Conference, 1996. IEEE; 01/1996