Recent advancements in the development of radiation hard semiconductor detectors for S-LHC
The proposed luminosity upgrade of the Large Hadron Collider (S-LHC) at CERN will demand the innermost layers of the vertex detectors to sustain fluences of about 1016 hadrons/cm2. Due to the high multiplicity of tracks, the required spatial resolution and the extremely harsh radiation field new detector concepts and semiconductor materials have to be explored for a possible solution of this challenge. The CERN RD50 collaboration “Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders” has started in 2002 an R&D program for the development of detector technologies that will fulfill the requirements of the S-LHC. Different strategies are followed by RD50 to improve the radiation tolerance. These include the development of defect engineered silicon like Czochralski, epitaxial and oxygen-enriched silicon and of other semiconductor materials like SiC and GaN as well as extensive studies of the microscopic defects responsible for the degradation of irradiated sensors. Further, with 3D, Semi-3D and thin devices new detector concepts have been evaluated. These and other recent advancements of the RD50 collaboration are presented and discussed.
Available from: Xiaopeng Wu
- "The most important measure of the detector radiation hardness is the Charge Collection Efficiency (CCE), which is mainly affected by the electric field distribution in the irradiated silicon, and the charge trapping by radiation-induced centers. At the expected maximum fluence of the strip sensor layers, the required full depletion voltage ( ) would be on the scale of thousand volts for a m thick oxygen-lean Float Zone silicon (Fz-Si) , , . Moreover, when heavily irradiated the Fz-Si undergoes Space Charge Sign Inversion (SCSI) in which the maximum electric field shifts from the segmented front side towards the back plane of the (p on n, or n-type sensor) structured sensor. "
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ABSTRACT: Tracking detectors for future high-luminosity particle physics experiments have to be simultaneously radiation hard and cost efficient. This paper describes processing and characterization of p+ /n-/n+ (n-type silicon bulk) detectors made of high-resistivity Magnetic Czochralski silicon (MCz-Si) substrates with 6-inch wafer diameter. The processing was carried out on a line used for large-scale production of sensors using standard fabrication methods, such as implanting polysilicon resistors to bias individual sensor strips. Special care was taken to avoid the creation of Thermal Donors (TD) during processing. The sensors have a full depletion voltage of 120-150 V which are uniform over the investigated sensors. All of the leakage current densities were below 55 nA/cm2 at 200 V bias voltage. A strip sensor with 768 channels was attached to readout electronics and tested in particle beam with a data acquisition (DAQ) similar to the system used by the CMS experiment at the CERN LHC. The test beam results show a signal-to-noise ratio greater than 40 for the test beam sensor. The results demonstrate that MCz-Si detectors can reliably be manufactured in the industrial scale semiconductor process.
Available from: Gunnar Lindstroem
- "For the S-LHC the detectors closest to the beam have to perform at hadron fluences up to several 10 16 cm −2 under complex , long term operation scenarios   . The limitations for their practical application in the hadron colliders are caused by irradiation induced defects leading to changes in the effective doping concentration (N e f f ) respectively full depletion voltage (V dep ), the reverse current at the depletion voltage (I dep ) and the degradation in the charge collection efficiency (CCE)          . "
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ABSTRACT: This work focuses on the investigation of radiation-induced defects responsible for the degradation of silicon detector performance. Comparative studies of the defects induced by irradiation with 60Co-γ rays, 6 and 15 MeV electrons, 23 GeV protons and reactor neutrons revealed the existence of point defects and cluster-related centers having a strong impact on damage properties of Si diodes. The detailed relation between the “microscopic” reasons as based on defect analysis and their “macroscopic” consequences for detector performance is presented. In particular, it is shown that the changes in the Si device properties (depletion voltage and leakage current) after exposure to high levels of 60Co-γ doses can be completely understood by the microscopically investigated formation of two point defects, a deep acceptor and a shallow donor, both depending strongly on the oxygen concentration in the silicon bulk. Specific for hadron irradiation are the annealing effects which decrease (increase) the originally observed damage effects as seen by the changes of the depletion voltage and these effects are known as “beneficial” and “reverse” annealing, respectively. A group of three cluster-related defects, revealed as deep hole traps, proved to be responsible specifically for the reverse annealing. Their formation is not affected by the oxygen content or silicon growth procedure suggesting that they are complexes of multi-vacancies located inside extended disordered regions.
Available from: Michael Moll
- "Only some specific topics of the RD50 scientific program will be described. More detailed information can be found in  , in recent conference proceedings     and in literature cited there. "
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ABSTRACT: The CERN RD50 collaboration “Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders” is developing radiation tolerant tracking detectors for the upgrade of the Large Hadron Collider at CERN (Super-LHC). One of the main challenges arising from the target luminosity of 1035 cm−2 s−1 are the unprecedented high radiation levels. Over the anticipated 5 years lifetime of the experiment a cumulated fast hadron fluence of about 1016 cm−2 will be reached for the innermost tracking layers. Further challenges are the expected reduced bunch crossing time of about 10 ns and the high track density calling for fast and high granularity detectors which also fulfill the boundary conditions of low radiation length and low costs. After a short description of the expected radiation damage after a fast hadron fluence of 1016 cm−2, several R&D approaches aiming for radiation tolerant sensor materials (defect and material engineering) and sensor designs (device engineering) are reviewed and discussed. Special emphasis is put on detectors based on oxygen-enriched Floating Zone (FZ) silicon, Czochralski (CZ) silicon and epitaxial silicon. Furthermore, recent advancements on SiC and GaN detectors, single type column 3D detectors and p-type detectors will be presented.
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