Influence of radiation defects on formation of thermal donors in silicon irradiated with high-energy helium ions

Isothermal annealing at temperatures from 370 to 410 °C was used for investigation of radiation enhanced formation of thermal donors in oxygen-rich FZ silicon irradiated with 7 MeV helium ions. Results show that formation of these defects is caused by hydrogen atoms which are diffusing from the anode contact. Hydrogen enhances diffusivity of interstitial oxygen and allows it to react with radiation defects containing vacancies and oxygen to form a new type of thermal donors. Their distribution is then given by concentration profile of radiation damage and diffusion length of hydrogen atoms. This effect occurs only in oxygen-rich silicon annealed in air and is absent in oxygen–lean silicon and samples annealed in vacuum.