Radiation hardness and charge collection efficiency of lithium irradiated thin silicon diodes

Abstract

Due to their low depletion voltage, even after high particle fluences, improved tracking precision and momentum resolution, and reduced material budget, thin substrates are one of the possible choices to provide radiation hard detectors for future high energy physics experiments. In the framework of the CERN RD50 Collaboration, we have developed PIN diode detectors on membranes obtained by locally thinning the silicon substrate by means of TMAH etching from the wafer backside. Diodes of different shapes and sizes have been fabricated on 50-/spl mu/m and 100-/spl mu/m thick membranes and tested, showing a low leakage current (of 300 nA/cm/sup 3/) and a very low depletion voltage (in the order of 1 V for the 50 /spl mu/m membrane) before irradiation. Radiation damage tests have been performed with 58 MeV lithium (Li) ions up to the fluence of 10/sup 14/ Li/cm/sup 2/ in order to determine the depletion voltage and leakage current density increase after irradiation. Charge collection efficiency tests carried out with a /spl beta//sup -/ particle source have been performed on both nonirradiated devices and samples irradiated up to 1.8/spl times/10/sup 13/ Li/cm/sup 2/. Results reported here confirm the advantages of thinned diodes with respect to standard 300-/spl mu/m thick devices in terms of low depletion voltage and high charge collection efficiency.