A new protocol to evaluate the charge collection efficiency degradation in semiconductor devices induced by MeV ion beam irradiation

(1) Physics Department, University of Torino, via Pietro Giuria 1, 10125 Torino, Italy
(2) International Atomic Energy Agency. Vienna International Centre, PO Box 100, 1400 Vienna, Austria and  Institute of Nuclear Research of the Hungarian Academy of Sciences, (ATOMKI), P.O. Box 51, H-4001 Debrecen, Hungary

Focussed MeV ion beams are ideal tools to investigate the effects of radiation induced displacement damage on the electronic performances of semiconductor device. Their main advantage is that ions can be used as projectiles to induce damage in the bulk material and as ionization probes to study the effects of radiation-induced defects on the charge collection efficiency. Actually, as a damaging tool, beside the broad energy range and ion type, i.e. ion range, they offer the advantage of a) a fine control of the ion beam current, b) an accurate determination of the ion fluence and c) area selective damage with high lateral resolution down to the micrometer scale.  In parallel, the Ion Beam Induced Charge (IBIC) technique provides a powerful experimental method to probe the electronic properties of semiconductor devices. By using suitable computational tools to predict ionization and defect production profiles as well as a robust model for the induced charge mechanism, the degradation of charge collection efficiency (CCE) as function of radiation displacement damage can be  properly interpreted and predicted. In order to exploit these advantages, an experimental protocol has been developed with the aim to establish a methodology for identifying key parameters that will subsequently allow the prediction of CCE degradation in the low damage (i.e. no-interaction between created defects) regime. Initially, the protocol was applied to Si pin diodes irradiated by focused MeV light ions.  Several experiments were performed in different laboratories using various ion-energy combinations both to induce defects and to probe their effects on the electronic performances of the devices. The experimental data were interpreted by a comprehensive theoretical model, based on the theory of charge induction in semiconductor devices, using as input parameters, the ionization and vacancy profiles calculated by the SRIM and MARLOWE codes. The model is capable to properly simulate the degradation of the charge collection efficiency in the low damage regime and suitable to extract key parameters, such as the carrier capture cross section, which are in good agreement with data available in the literature or evaluated through other complementary techniques (i.e. DLTS). The potential of the experimental and theoretical methodology is finally discussed through several examples to compare the intrinsic radiation hardness of different materials and devices.  

This work was carried out within the International Atomic Energy Agency (IAEA) coordinated research project (CRP No. F11016) on “Utilization of Ion Accelerators for Studying and Modelling Ion Induced Radiation Defects in Semiconductors and Insulators”.