Radiation hardness studies of epitaxial diodes for the PANDA micro-vertex-detector

PANDA is a key experiment of the future FAIR facility, under construction in Darmstadt, Germany. It will study the collisions between an antiproton beam and a fixed proton or nuclear target. The Micro Vertex Detector (MVD) is its innermost detector and is composed of four concentric barrels and six forward disks, instrumented with silicon hybrid pixel and double-sided microstrip detectors. It serves the identification of primary and secondary vertices. The main requirements include high spatial and time resolution, trigger-less readout with high rate capability, good radiation tolerance and low material budget. In order to investigate the radiation hardness of the silicon pixel sensors, irradiation studies were performed on diodes using a proton beam at the Bonn Isochronous Cyclotron. The diodes featured an epitaxial layer grown on a Czochralski substrate; the thicknesses of the epitaxial layers were 100μ m and 150μ m, respectively. Additionally, some of the samples were treated with an oxygenation process. The study was performed with two different fluences, comparing the I-V and C-V curves of the non-irradiated diodes with the ones obtained immediately after the irradiation and after an annealing phase.