Magnetic field effects on Hybrid PhotoDiode single electron response

Hybrid PhotoDiodes (HPDs) are very simple photo detectors which cover the a pplicability field of Photo Multipliers but show some better features. In p articular HPDs show a very good photon counting capability, due to their pe culiar one-stage gain process. It was found that HPD's photoelectron spectr um has a low-energy continuum which could be attributed to a backscattering process from the diode surface. In order to clearly distinguish the exact role of backscattering, the single photoelectron response (SER) of a 61 pix el proximity focused HPD was measured in standard conditions and in a 5 kG axial magnetic held. The results clearly indicate that the backscattering p rocess gives the greatest contribution to the low-energy continuum spectrum . Monte Carlo simulations, using the EGS4 code, supported the analysis and allowed some interpretation of the effect, which greatly depends on diode s urface characteristics, such as contact layer thickness. (C) 2000 Elsevier Science B.V. All rights reserved.