SYSTEMATIC STUDY OF MASSIVE GERMANIUM PIN DIODE DETECTORS AT 20 MK

To investigate the properties and improve the performances of bolomete rs with simultaneous measurement of ionization for dark matter search, we have realized 6 g and 70 g germanium PIN diodes with thin (35-80 n m) B and P implanted faces on 4 and 10 mm thick ultrapure germanium pl ates. The faces were characterized by LT sheet resistance measurements , ellipsometry, SIMS and RES, and the bulk by carriers lifetime and ca pacitance measurements. We found a diode behaviour at 20 mK and 4.2 K. We made a systematic study of the response to photons from 5 to 105 k eV at 0.02, 0.08 and 4.2 K, for polarization voltages from 0 to 10 V. Our main purpose was to study the slow time evolutions of the pulse he ights which characterize the behaviour of such detectors at very low t emperatures. We obtained a threshold of 4 keV, a resolution of 0.76 ke V (rms), and a stability better than 1 hour, with a polarization volta ge V = 0.2 V on a 4 mm thick diode. Similar resolutions were obtained with a 10 mm thick diode, but the time stability was worse. We found t hat most of the carriers are drifting across the 4 mm diode for V = 0. A possible contribution of a built-in potential to the pulses time ev olution is evoked. We also studied the incomplete carriers collection close to the edges.