Influence of heavy ion irradiation damage on silicon charged particle detector calibration

The full analytical potential of heavy ion backscattering and elastic recoil detection analysis (ERDA) depends critically on establishing a reliable energy calibration. In order to make accurate measurements of thin film samples we have investigated the changes in the energy calibration of a Si p⁺-n-n⁺ charged particle detector subjected to heavy ion irradiation over 24 h in a time of flight-energy elastic recoil detection analysis (ToF-E ERDA) measurement. In this study a set of similar Al/ZrO₂/Zr samples were analysed sequentially with 60 MeV ¹²⁷I¹¹⁺ ions. The calibration change for ¹⁶O, ²⁷Al and ^90-92,95,96Zr were monitored by tagging individual recoils with their energy derived from the ToF. The calibration parameters for a wider range of elements (Li-Ag) were measured before and after the sequential irradiation with O, Al, Zr and I atoms. The results show that the change in the calibration could be characterised by an increase in the energy interval spanned by one channel and a slight decrease in the channel zero energy. The calibration shift for a given projectile atomic number depends linearly on the fluence of heavy particles impinging on the detector and the consequential increase in detector leakage current. This indicates that for similar irradiation conditions, a correction to account for the calibration shift may be simply determined for each sample from the number of heavy recoil counts registered or from the change in leakage current. Furthermore, the silicon charged particle detector calibration depends on recoil atomic number both before, and after, the heavy ion irradiation. The fluence-induced calibration shift for different recoils can be described by a linear dependence on recoil atomic number.