Charge carrier avalanche multiplication in high-voltage diodes triggered by ionizing radiation

Non-destructive strong carrier avalanche multiplication reaching levels up to four orders of magnitude as compared to the initially deposited charge was investigated in high-voltage diodes for a variety of initiating high-energy ions and for high-energy protons. Current levels of several amperes were detected with the current flowing only over time periods up to 50 ns. This indicates that no internal feedback mechanism was involved. From measurements of the generated charge for various irradiation conditions it is deduced that the threshold voltage level for avalanche multiplication to set in depends on the type of ion and on the penetration depth of the ions, with the lowest threshold value occurring when the depth reaches slightly beyond the pn-junction into the n-base. However, for comparable initiating conditions the generated charge appears to depend only on the applied voltage and not on the ion used. Two-dimensional device simulations of the temporal evolution of the field distribution and the carrier distribution were performed. They showed the basic behavior of the multiplication process, in that an avalanching high field strength region detaches itself from a location near the pn-junction and moves all the way across the n-base, in some respects similar to streamers in gas discharges.