A. Rolf

Bio: A. Rolf is an academic researcher from Technical University of Dortmund. The author has contributed to research in topics: Silicon & Electric field. The author has an hindex of 7, co-authored 9 publications receiving 251 citations.

Strip detector design for ATLAS and HERA-B using two-dimensional device simulation

Abstract: Irradiation scenarios were simulated in order to evaluate different technology and design options for silicon strip detectors exposed to a high luminosity environment. Two-dimensional process and device simulations were performed to get an insight into the device behaviour. The boundary condition of the free oxide regions between the strips was evaluated thoroughly to obtain correct field distributions. Using these results the formation of electron accumulation layers on the surface of the p-side and the depletion voltage dependence on the strip geometry can be explained. We investigated the “blocking implant” and the “spray implant” techniques as promising candidates for the n-side isolation of irradiated detectors. The main drawback of the “blocking implanted” devices is the increase of the electric field with increasing oxide charges. This implies the danger of impact ionization in irradiated devices. A “spray implanted” isolation layer leads to the highest electric field in the non-irradiated state which has the advantage of a better testability. Small gaps between strips as used in charge division readout reduce electric fields and leakage currents.

Damage-induced surface effects in silicon detectors

Abstract: One of the main applications of silicon detectors in future collider experiments is their use in the tracking area. In addition to the very intense hadron flux (both neutral and charged) causing bulk damage, a severe effect by ionizing radiation has also to be envisioned at small radii. In the present study results obtained after irradiation with low energetic electrons (20 keV) are presented. In this case bulk damage can be completely excluded. Effects on the oxide charge and density of interface states are characterized by C—V and I—V measurements. In addition the corresponding changes of the space charge region are observed with a scanning proton micro beam. The electric field distribution, the depletion depth and the lateral extension of the depletion region is thus investigated and the results are compared with detailed simulations using the ToSCA-program.

Pion-induced damage in silicon detectors

Abstract: The damage induced by pions in silicon detectors is studied for positive and negative pions for fluences up to 1014 cm−2 and 1013 cm−2, respectively. Results on the energy dependence of the damage in the region of 65 to 330 MeV near to the Δ resonance are presented. The change in detector characteristics such as leakage current, charge collection efficiency and effective impurity concentration including long-term annealing effects have been studied. Comparisons to neutron- and proton-induced damage are presented and discussed.

Neutron irradiation of silicon diodes at temperatures of +20°C and −20°C

Abstract: We report measurements of the behaviour of silicon diodes when exposed to integrated neutron doses of up to 5 × 10 13 neutron/cm 2 . The measurements have been made at diode temperatures between room temperature and −20°C. From measurements of the diode leakage current and depletion voltage, and consequent evaluations of the effective impurity concentration, the temperature dependence of these quantities is discussed in terms of the annealing behaviour of the diodes. Comments are made on the suitability of silicon as a detector medium for particle physics experiments at future accelerators.

Radiation induced bulk damage in silicon detectors

Abstract: The paper discusses the current status of radiation damage to the bulk material of silicon detectors. In particular the main effects of current increase, change in the effective charge carrier density and its effect on the operation voltage, and the signal charge collection in silicon detectors are reviewed. Detailed measurements have allowed parametrization of the effects, which are in turn used to simulate long term performance of detectors in the environment expected in future hadron collider experiments. Recent results on pion damage measurements are highlighted. Studies aimed at reducing systematic errors inherent in comparing analyses of different groups are discussed, as are possible indications of material dependent effects from recent measurements.

ATLAS pixel detector electronics and sensors

Abstract: The silicon pixel tracking system for the ATLAS experiment at the Large Hadron Collider is described and the performance requirements are summarized. Detailed descriptions of the pixel detector electronics and the silicon sensors are given. The design, fabrication, assembly and performance of the pixel detector modules are presented. Data obtained from test beams as well as studies using cosmic rays are also discussed.

Advances in solid state photon detectors

Abstract: Semiconductor photodiodes were developed in the early `Forties approximately at the time when the photomultiplier tube became a commercial product (RCA 1939) Only in recent years, with the invention of the Geiger-mode avalanche photodiodes, have the semiconductor photo detectors reached sensitivity comparable to that of photomultiplier tubes The evolution started in the `Sixties with the p-i-n (PIN) photodiode, a very successful device, which is still used in many detectors for high energy physics and a large number of other applications like radiation detection and medical imaging The next step was the development of the avalanche photodiode (APD) leading to a substantial reduction of noise but not yet achieving single photon response The weakest light flashes that can be detected by the PIN diode need to contain several hundreds of photons An improvement of the sensitivity by 2 orders of magnitude was achieved by the development of the avalanche photodiode, a device with internal gain At the end of the millennium, the semiconductor detectors evolved with the Geiger-mode avalanche photodiode into highly sensitive devices, which have an internal gain comparable to the gain of photomultiplier tubes and a response to single photons A review of the semiconductor photo detector design and development, the properties and problems, some applications and a speculative outlook on the future evolution will be presented

Radiation damage in silicon detectors

Abstract: Radiation damage effects in silicon detectors under severe hadron and gamma-irradiation are surveyed, focusing on bulk effects. Both macroscopic detector properties (reverse current, depletion voltage and charge collection) as also the underlying microscopic defect generation are covered. Basic results are taken from the work done in the CERN-RD48 (ROSE) collaboration updated by results of recent work. Preliminary studies on the use of dimerized float zone and Czochralski silicon as detector material show possible benefits. An essential progress in the understanding of the radiation-induced detector deterioration had recently been achieved in gamma irradiation, directly correlating defect analysis data with the macroscopic detector performance.

Simulation of non-ionising energy loss and defect formation in silicon

Abstract: Simulation studies of Non-Ionising Energy Loss (NIEL) in silicon exposed to various types of hadron irradiation are presented. A simulation model of migration and clustering of the produced primary defects is developed. Although there are many uncertainties in the input parameters it is shown that the model is consistent with experimental observations on standard and oxygen-enriched silicon. However, the model makes the rather dramatic prediction that NIEL scaling of leakage current and effective doping concentration can be violated significantly even in standard silicon. Although there are possible shortcomings in the model which might account for this, it is shown that at the microscopic level there is, indeed, no obvious reason for an exact NIEL scaling. Furthermore, it is argued that, contrary to common belief, even a significant violation of NIEL scaling can still be consistent with experimental data.

The silicon microstrip sensors of the ATLAS semiconductor tracker

Abstract: This paper describes the AC-coupled, single-sided, p-in-n silicon microstrip sensors used in the Semiconductor Tracker (SCT) of the ATLAS experiment at the CERN Large Hadron Collider (LHC) The sensor requirements, specifications and designs are discussed, together with the qualification and quality assurance procedures adopted for their production The measured sensor performance is presented, both initially and after irradiation to the fluence anticipated after 10 years of LHC operation The sensors are now successfully assembled within the detecting modules of the SCT, and the SCT tracker is completed and integrated within the ATLAS Inner Detector Hamamatsu Photonics Ltd supplied 922percent of the 15,392 installed sensors, with the remainder supplied by CiS