Publications (9)0 Total impact
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Article: X-ray induced radiation damage in segmented p+n silicon sensors
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ABSTRACT: Experiments at the European X-ray Free Electron Laser (XFEL) require silicon pixel sensors which have to meet extraordinary requirements for experiments at the XFEL. This paper shortly describes the requirements and challenges for silicon sensors at the European XFEL and addresses the efforts made by the detector group of Hamburg University for the sensor development. In particular, the main results on the X-ray induced radiation damage are presented.Proceeding of Science. 04/2013; VERTEX 2012(019):1-7. -
Article: Study of the accumulation layer and charge losses at the Si-SiO2 interface in p+n-silicon strip sensors
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ABSTRACT: Using the multi-channel Transient Current Technique the currents induced by electron-hole pairs, produced by a focussed sub-nanosecond laser of 660 nm wavelength close to the Si-SiO2 interface of p+n silicon strip sensors have been measured, and the charge-collection efficiency determined. The laser has been operated in burst mode, with bursts typically spaced by 1 ms, each consisting of 30 pulses separated by 50 ns. In a previous paper it has been reported that, depending on X-ray-radiation damage, biasing history and humidity, situations without charge losses, with hole losses, and with electron losses have been observed. In this paper we show for sensors before and after irradiation by X-rays to 1 MGy (SiO2), how the charge losses change with the number of electron-hole pairs generated by each laser pulse, and the time interval between the laser pulses. This allows us to estimate how many additional charges in the accumulation layers at the Si-SiO2 interface have to be trapped to significantly change the local electric field, as well as the time it takes that the accumulation layer and the electric field return to the steady-state situation. In addition, results are presented on the change of the pulse shape caused by the plasma effect for high charge densities deposited close to the Si-SiO2 interface.02/2013; -
Article: Challenges for Silicon Pixel Sensors at the European XFEL
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ABSTRACT: A systematic experimental study of the main challenges for silicon-pixel sensors at the European XFEL is presented. The high instantaneous density of X-rays and the high repetition rate of the XFEL pulses result in signal distortions due to the plasma effect and in severe radiation damage. The main parameters of X-ray-radiation damage have been determined and their impact on p+n sensors investigated. These studies form the basis of the optimized design of a pixel-sensor for experimentation at the European XFEL.12/2012; -
Article: The single photon sensitivity of the Adaptive Gain Integrating Pixel Detector
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ABSTRACT: Single photon sensitivity is an important property of certain detection systems. This work investigated the single photon sensitivity of the Adaptive Gain Integrating Pixel Detector (AGIPD) and its dependence on possible detector noise values. Due to special requirements at the European X-ray Free Electron Laser (XFEL) the AGIPD finds the number of photons absorbed in each pixel by integrating the total signal. Photon counting is done off line on a thresholded data set. It was shown that AGIPD will be sensitive to single photons of 8 keV energy or more (detection efficiency $\gg$ 50%, less than 1 count due to noise per 10$^6$ pixels). Should the final noise be at the lower end of the possible range (200 - 400 electrons) single photon sensitivity can also be achieved at 5 keV beam energy. It was shown that charge summing schemes are beneficial when the noise is sufficiently low. The total detection rate of events is increased and the probability to count a single event multiple times in adjacent pixels is reduced by a factor of up to 40. The entry window of AGIPD allows 3 keV photons to reach the sensitive volume with approximately 70% probability. Therefore the low energy performance of AGIPD was explored, finding a maximum noise floor below 0.035 hits/pixel/frame at 3 keV beam energy. Depending on the noise level and selected threshold this value can be reduced by a factor of approximately 10. Even though single photon sensitivity, as defined in this work, is not given, imaging at this energy is still possible, allowing Poisson noise limited performance for signals significantly above the noise floor.03/2012; -
Article: Simulation study of the impact of AGIPD design choices on X-ray Photon Correlation Spectroscopy utilizing the intensity autocorrelation technique
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ABSTRACT: The European XFEL, currently under construction, will produce a coherent X-ray pulse every 222 ns in pulse trains of up to 2700 pulses. In conjunction with the fast 2D area detectors currently under development, it will be possible to perform X-ray Photon Correlation Spectroscopy (XPCS) experiments on sub-microsecond timescales with non-ergodic systems. A case study for the Adaptive Gain Integrating Pixel Detector (AGIPD) at the European XFEL employing the intensity autocorrelation technique was performed using the detector simulation tool HORUS. As optimum results from XPCS experiments are obtained when the pixel size approximates the (small) speckle size, the presented study compares the AGIPD (pixel size of (200 $\upmu$m)$^2$) to a possible apertured version of the detector and to a hypothetical system with (100 $\upmu$m)$^2$ pixel size and investigates the influence of intensity fluctuations and incoherent noise on the quality of the acquired data. The intuitive conclusion that aperturing is not beneficial as data is 'thrown away' was proven to be correct for low intensities. For intensities larger than approximately 1 photon per (100 $\upmu$m)$^2$ aperturing was found to be beneficial, as charge sharing effects were excluded by it. It was shown that for the investigated case (100 $\upmu$m)$^2$ pixels produced significantly better results than (200 $\upmu$m)$^2$ pixels when the average intensity exceeded approximately 0.05 photons per (100 $\upmu$m)$^2$. Although the systems were quite different in design they varied in the signal to noise ratio only by a factor of 2-3, and even less in the relative error of the extracted correlation constants. However the dependence on intensity showed distinctively different features for the different systems.08/2011; -
Article: Properties of a radiation-induced charge multiplication region in epitaxial silicon diodes
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ABSTRACT: Charge multiplication (CM) in p$^+$n epitaxial silicon pad diodes of 75, 100 and 150 $\upmu$m thickness at high voltages after proton irradiation with 1 MeV neutron equivalent fluences in the order of $10^{16}$ cm$^{-2}$ was studied as an option to overcome the strong trapping of charge carriers in the innermost tracking region of future Super-LHC detectors. Charge collection efficiency (CCE) measurements using the Transient Current Technique (TCT) with radiation of different penetration (670, 830, 1060 nm laser light and $\alpha$-particles with optional absorbers) were used to locate the CM region close to the p$^+$-implantation. The dependence of CM on material, thickness of the epitaxial layer, annealing and temperature was studied. The collected charge in the CM regime was found to be proportional to the deposited charge, uniform over the diode area and stable over a period of several days. Randomly occurring micro discharges at high voltages turned out to be the largest challenge for operation of the diodes in the CM regime. Although at high voltages an increase of the TCT baseline noise was observed, the signal-to-noise ratio was found to improve due to CM for laser light. Possible effects on the charge spectra measured with laser light due to statistical fluctuations in the CM process were not observed. In contrast, the relative width of the spectra increased in the case of $\alpha$-particles, probably due to varying charge deposited in the CM region. Comment: 11 pages, accepted by NIMA07/2010; -
Article: Measurements of charge carrier mobilities and drift velocity saturation in bulk silicon of <111> and <100> crystal orientation at high electric fields
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ABSTRACT: The mobility of electrons and holes in silicon depends on many parameters. Two of them are the electric field and the temperature. It has been observed previously that the mobility in the transition region between ohmic transport and saturation velocities is a function of the orientation of the crystal lattice. This paper presents a new set of parameters for the mobility as function of temperature and electric field for <111> and <100> crystal orientation. These parameters are derived from time of flight measurements of drifting charge carriers in planar p^+nn^+ diodes in the temperature range between -30{\deg}C and 50{\deg}C and electric fields of 2x10^3 V/cm to 2x10^4 V/cm.07/2010; -
Article: Simulation and Experimental Study of Plasma Effects in Planar Silicon Sensors
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ABSTRACT: In silicon sensors high densities of electron-hole pairs result in a change of the current pulse shape and spatial distribution of the collected charge compared to the situation in presence of low charge carrier densities. This paper presents a detailed comparison of numerical simulations with time resolved current measurements on planar silicon sensors using 660~nm laser light to create different densities of electron hole pairs. Comment: Revised Version after peer-review07/2010; -
Article: Charge Multiplication Properties in Highly Irradiated Epitaxial Silicon Detectors
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ABSTRACT: Charge multiplication (CM) occuring in highly radiation-damaged Si sensors is currently under discussion as an option to overcome the strong trapping of charge carriers in the innermost pixel layers of future Super-LHC detectors. In this work, CM was studied in p + -n epitaxial silicon pad diodes of 75, 100 and 150 µm thickness after 24 GeV/c proton irradiation with 1 MeV neutron equivalent fluences in the order of 10 16 cm −2 . Basic properties like the development and location of the CM region, proportionality between measured and deposited charge, spatial uniformity and long-term stability, which were studied with charge collection efficiency (CCE) measurements us-ing the Transient Current Technique (TCT), are reviewed. Using 90 Sr β -particles and an amplifier with 25 ns shaping time the signal in the CM regime for radiation similar to minimum ionising particles was investigated. Also associated noise, signal-to-noise ratio and effects of CM on the charge spectrum were studied.PoSVERTEX. 01/2010;
Top co-authors
Institutions
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2010
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Universität Hamburg
- Institut für Experimentalphysik
Hamburg, Hamburg, Germany
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