Comparative investigation of recombination characteristics in proton and electron irradiated Si structures

Abstract

Comparative analysis of the carrier recombination and generation lifetime as well as reverse recovery durations (RR), dependent on electron and proton irradiation fluence, has been performed in float zone (FZ) silicon PIN diodes and wafer structures. These investigations have been devoted to determination of the dominant radiation defects and their depth distribution, to design the irradiation technology steps for PIN diodes with fast switching rates. The samples were irradiated with 2 MeV protons and 5–10 MeV electrons with fluences in the range of 7·10¹²–7·10¹⁴ p/cm² as well as 2.4·10¹²–5.2·10¹³ e/cm², respectively. Carrier decay constituents and values of recombination lifetime have been evaluated by employing a microwave probed photoconductivity transient technique (MW-PC), while deep levels spectra ascribed to generation lifetime variations have been examined by exploiting capacitance deep level transient spectroscopy (C-DLTS). Recombination lifetime decreases from several microseconds to few nanoseconds in the proton irradiated Si, while DLTS spectra show an increase of the amplitude of a DLTS peak at 170 K with irradiation fluence. This peak dominates within DLTS spectra where peaks at 90, as well as at 140 and 250 K, ascribed to vacancy attributed defects, are also present. Recombination lifetime decreases from tens to few microseconds, while vacancy ascribed defects dominate in DLTS spectra under increase of irradiation fluence for the same material irradiated with electrons. Sharply inhomogeneous depth distribution of recombination lifetime in proton irradiated samples has been revealed from the cross-sectional scans of the excess carrier lifetime measured by MW-PC technique. This indicates a formation of the -layer of enhanced recombination in vicinity of the p⁺–n junction of PIN diodes. Meanwhile, the recombination lifetime is nearly constant within depth of the electron irradiated Si samples. These characteristics correlate rather well with reverse recovery time constants of the same PIN diodes.
Keywords: carrier lifetime, reverse recovery time, microwave probed photoconductivity, deep level transient spectroscopy, proton and electron irradiations, radiation defects
PACS: 61.72.Ji, 61.82.Fk, 72.40.+w