MINORITY CARRIER LIFETIME AND POTENTIAL BARRIER HEIGHT IN POLYCRYSTALLINE SILICON : EFFECTS OF LOW TEMPERATURE ANNEALINGS AND NEUTRON IRRADIATION

Abstract

The effects of annealing, at temperatures ≤450°C under argon or hydrogen atmosphere, and of 14 MeV neutron irradiation on bulk lifetime τv of minority carriers and height ϕB of the potential barrier regions are compared. The measurements essentially involve transient photocurrent and photoconductivity responses, and I (V,T) characteristics, of samples from large grain R.A.D. ribbons (CZ silicon, boron doped, 1Ω.cm). The results show that the low temperature annealing with argon or hydrogen scarcely modifies both the τv (1 to 0,5µ s) and ϕB (~ 0.10 to 0,20 eV) values. But the effects of the regions with potential barriers ϕB on the material conductivity only agree with the double-Schottky barrier model when the samples have not been annealed under hydrogen : by passivating grain boundaries near the sample surface, hydrogen makes the effects of the remaining barrier regions analoguous to the effects of insulating zones. Following neutron irradiation the behaviour of the electrical properties of the material is again strongly related to the behaviour of the potential barrier regions : - the degradation of τvappears comparable to the degradation observed in single-cristalline samples ; - the variations of ϕBare responsible for the change in sample conduction which is observed at the low irradiation doses where single-cristal conductivity is not affected.