A. Chilingarov

Silicon microstrip detectors for the ATLAS SCT

Abstract The ATLAS Semiconductor Tracker at the Large Hadron Collider (LHC) will incorporate ∼20,000 individual silicon microstrip sensors representing ∼60 m 2 of silicon. Production and delivery of the sensors is already underway and scheduled for completion by late 2002. The sensors have been optimised for operation in the harsh radiation environment of the LHC, and subjected to an extensive qualification program in which their pre- and post-irradiation characteristics have been evaluated. The sensor design features are reviewed, together with their electrical characteristics and the Quality Control procedures adopted by ATLAS during production.

Radiation damage due to NIEL in GaAs particle detectors

Abstract The Non-Ionizing Energy Loss (NIEL) for fast neutrons, protons and pions in GaAs has been estimated from published calculations. The values are then used to search for a correlation between the observed reduction of charge collection efficiency (CCE) in GaAs particle detectors with the radiation dose from NIEL. A correlation is demonstrated to be present for detectors made from a wide range of material. The implications for the performance of GaAs detectors at the Large Hadron Collider (LHC) are discussed.

A new method of carrier trapping time measurement

Abstract A new method of measuring carrier trapping time by a simple analysis of the current pulse shape is proposed and demonstrated for irradiated silicon detectors. This method which we call Exponentiated Charge Crossing (ECC) requires no knowledge of either the electric field profile in the detector or of the relation between the carrier drift velocity and the electric field. It is general enough to be valid not only for solid-state particle detectors but also for other devices such as some gaseous and liquid detectors. The results obtained by the proposed method are consistent with those obtained by an earlier method.

The electric field in irradiated silicon detectors

The electric field distribution inside heavily irradiated silicon particle detectors is deduced using observations of α particle and minimum ionising particle signals. In these detectors α particle signals are observed for both p+ and n+ side illumination even when the detector is only partially depleted. The observations indicate that the electric field distribution within the partially depleted detector has the contribution expected from a uniform space charge, as in unirradiated detectors, together with a strong, short range, local electric field in the vicinity of the p+ electrode and a non-zero electric field in the remaining part of the detector.

Pion-induced damage in silicon detectors

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.

Simulation of charge collection and sharing in microstrip detectors

Abstract The various mechanisms which can cause broadening of the signal distribution in a microstrip detector are discussed, in turn, via a simple simulation. Some analytic results for calculating the effect of dead areas are also presented. A comparison is made of GaAs test beam data with the results of the simulation.

OPERATION OF HEAVILY IRRADIATED SILICON DETECTORS UNDER FORWARD BIAS

Abstract Test diodes made of detector grade Si have been irradiated by fluences up to 2.8 × 10 14 1 MeV neutrons per cm 2 . We observe that signals from minimum ionising particles are produced with high charge collection efficiency (CCE∼70%) at relatively low forward bias voltages. The more usual reverse bias requires ∼10 times larger voltage to produce similar CCE.

Frequency and temperature dependence of the depletion voltage from CV measurements for irradiated Si detectors

Abstract The dependence on measurement frequency and temperature of the depletion voltage extracted in the standard way from the CV characteristics of heavily irradiated silicon detectors is studied, parameterised and fitted. A similar pattern of behaviour is observed for a wide range of analysed detectors. A formula is derived which allows correction of the depletion voltage from one frequency–temperature point to another.

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.

Displacement energy for various ions in particle detector materials

Abstract The total displacement energy or total non-ionising energy loss has been calculated for a variety of ions during their slowing down to rest in the detector materials carbon, silicon and gallium arsenide. The calculations, based on the theory of Lindhard et al., have been performed using a Monte Carlo method and a simple parameterisation of the results is presented. Such a parameterisation will simplify considerably the future computation of the differential non-ionising energy loss by fast particles in particle detectors.