Lifetime degradation on n-type wafers with boron-diffused and SiO2/SiN-passivated surface

We observe minority carrier lifetime degradation in n-type wafers with boron-diffused surface and SiO2/SiN passivation when exposed to illumination or thermal aging. This degradation is not observed on control wafers with phosphorus-diffused surfaces and identical passivation under the same treatment. Boron-diffused wafers with Si-rich SiN or Al2O3 passivation do not degrade either. Both boron-diffused layer and SiO2/SiN are thus necessary to observe this degradation. Experiments on different aging conditions indicate that the degradation is due to a thermal effect accelerated by injection of excess carriers.