Stability of vacancies in silicon irradiated by xenon ions at 77 K

Phosphorus-doped Si ([P]=3.5x1015 cm-3) has been irradiated at GANIL by 3.5 GeV Xe ions presenting an electronic stopping power of 11 MeV/μm. The irradiation has been performed at LN2 temperature in the fluence range 3x109-9x1010 ions/cm2. In situ measurements show that the resistance R of the samples increase with the fluence φt during the whole irradiation. This behaviour can be principally explained by the introduction of point defects which compensate the free carrier concentration. In n-type silicon the most common electrically active centers induced by irradiation are the vacancy, the divacancy, and the oxygen-vacancy and phosphorus-vacancy complexes. For each defect, it is possible to compute a R-φt curve and to obtain the corresponding introduction rate (ratio of the concentration to the fluence) by comparing this curve with the experimental one. The simulation indicates that the carriers are mainly trapped on vacancies. Therefore, the stability of this primary defect at LN2 temperature is shown using in situ resistance measurements. (orig.)