Degradation and regeneration of radiation-induced defects in silicon: A study of vacancy-hydrogen interactions

Silicon lattice vacancies exist in all silicon wafers, will increase in concentration due to high temperature processing, can form recombination active defects and have been proposed as a possible candidate for LeTID. Despite this, there have been relatively few studies in the solar field dedicated to investigating vacancies, their recombination properties or their interaction with hydrogen. In this work, we use high energy electron radiation to create large numbers of vacancies in silicon and study the lifetime response to subsequent thermal processes in the presence or absence of bulk hydrogen. The radiation results in the formation of radiation-induced defects which we interpret as being related to the creation of vacancies in the silicon bulk. Modelling of injection dependent minority carrier lifetime finds that the defects formed via this radiation process have different Shockley-Read-Hall properties to LeTID and are as such, unlikely to be related. Furthermore, this defect can be removed during low temperature annealing but only if hydrogen is present in the bulk of the silicon wafers. This is in contrast to samples with no bulk hydrogen which do not recover during low temperature annealing. The study thus finds no evidence for any link between LeTID and vacancies in silicon, but it does demonstrate the ability of hydrogen to repair radiation damage.