Radiation hard amorphous silicon particle sensors
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Radiation hard amorphous silicon particle sensors N. Wyrsch1, C. Miazza1, S. Dunand1, C. Ballif1, A. Shah1, M. Despeisse2, D. Moraes2, P. Jarron2, 1 Institut de Microtechnique, Université de Neuchâtel, Breguet 2, 2000 Neuchâtel, Switzerland, 2 CERN, CERN Meyrin, 1211 Genève 23, Switzerland, ABSTRACT Radiation tests of 32 µm thick hydrogenated amorphous silicon n-i-p diodes have been performed using a high energy 24 GeV proton beam up to fluences in excess of 1016 protons/cm2. The results are compared to irradiation of similar 1 µm and 32 µm thick n-i-p diodes using a proton beam of 280 keV at a fluence of 3x1013 protons/cm2. Even though both types of irradiation cause a significant drop in photoconductivity of thin or thick diodes, all samples survived the experiment and recover almost fully after a subsequent thermal annealing. INTRODUCTION The future generation of colliders (in the field of high energy physics) will give rise to very challenging demands regarding particle detectors, such as extreme radiation hardness, interconnection density, integration and cost. In this context, vertically-integrated sensors based on the deposition of a thick hydrogenated amorphous silicon (a-Si:H) diode on top of a readout ASIC (Application-Specific Integrated Circuit) are seen as a promising solution. Such verticallyintegrated radiation sensors are a particularly interesting example of so-called “thin-film on ASIC” or “TFA” technology. Recently, the authors have successfully developed TFA sensors, aiming at the detection of single charge particles (β particles and protons) at the minimum ionizing energy (MIP) [1, 2]. For these applications, the high radiation hardness of a-Si:H is a particularly attractive feature. Several irradiation tests have been performed in the past using proton [3, 4, 5, 6] or neutron irradiation [7] on thin p-i-n devices, thereby investigating in most cases the effect on the photovoltaic properties. One has to note that most radiation tests were performed with the goal of assessing the hardness of a-Si:H solar cells to (relatively) low energy protons for space applications. In thin devices, the effect of proton, neutron or photon irradiation has very similar consequences on material and diode properties. Light-soaking of an a-Si:H layer or diode induces the creation of metastable deep defects than can be annealed out. A similar behavior has been observed so far for irradiation tests. However, up to now only scattered experiments have been carried out and we lack insight into the effect of irradiation on detector properties; little was also so far known on the limits of this technology in very harsh environments. In the present work, we first tried to investigate the limits of a-Si:H thick diodes under high energy proton beam at the fluences that are expected for detectors in future generations of particle colliders. Similar thick diodes as well as thin ones were also degraded using low energy proton beams and lower fluences as a means of comparison with earlier irradiation experiments publishe
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