Positive temperature coefficient of impact ionization in strained-Si

We have experimentally studied impact ionization (II) in the strained-Si layer of a strained-Si/SiGe heterostructure. Our key finding is that the impact ionization multiplication coefficient has a positive temperature coefficient which is opposite to that of bulk Si. Furthermore, the temperature dependence of the multiplication coefficient has been found to be exponential in nature. Our experimental work shows that the combination of a strong and positive temperature dependence of the II coefficient and the significant self-heating that this structure suffers from results in an overall impact ionization rate that is more than an order of magnitude higher than that of reference Si devices operating under identical bias conditions.