The effects of X-rays on p-n junction leakage currents

The effects of X-ray exposure on two types of p-n junction leakage current are presented. X-rays generate surface states at the oxide-silicon interface and lower the junction electric field at the surface. As a result, the usual field-insensitive generation-recombination current (type 1) increases and the field-sensitive leakage current (type 2) decreases. The type 1 current increases linearly with the incident energy density. From the increment of the type 1 leakage, the surface recombination velocity increases by 1*10³ cm/s for every 120 mJ/cm² of incident X-ray exposure. Some surface states are responsible for the reduction of the surface electric field and thus the surface component of the type 2 current. The results resemble that of the late stage of hot-carrier stress. The surface states affecting these two types of leakage have different annealing properties. The ones that increase the type 1 current can be annealed out with a short heat cycle, while the ones that lower the type 2 current require a very long heat cycle to remove.