Investigation of charge collection in a silicon PIN photodiode

Ion Beam Induced Charge (IBIC) imaging with a 2 MeV He+ microbeam has been used to investigate spectroscopic features and charge transport properties of a Hamamatsu S1223 silicon PIN photodiode. Pulse height spectra were collected with high lateral resolution at different reverse bias values between 0 V and −100 V. Pulse height maps and median energy maps were generated to observe the spatial variations of charge collection properties. Absolute charge collection efficiency was calculated along a line including the edge structure of the photodiode. Our results show that the charge collection is uniform within the sensitive area of the PIN diode but it is decreasing close to the edges. There are low energy satellite peaks and other structures in the spectra due to energy loss in the edge protecting surface coverages and incomplete charge collection in the near surface and undepleted regions. The investigated effects contribute to the further understanding of the operation of the Si photodiode and similar semiconductor device structures.