INVESTIGATIONS OF DONOR AND ACCEPTOR REMOVAL AND LONG-TERM ANNEALING IN SILICON WITH DIFFERENT BORON PHOSPHORUS RATIOS/

Studies of radiation damage of silicon detectors have shown that in mo st elementary particle physics applications, the major problem caused by non-ionizing interactions in silicon will be the change in the conc entration of the electrically active impurity states. For many silicon applications in high radiation environments, the increase in the rela tive acceptor concentration during long term room temperature annealin g is the limiting factor. The first step in developing radiation harde ned silicon is to identify the defects which are responsible for this effect. In earlier work, we developed a model which describes the expe rimentally observed fast neutron induced changes in the net electrical ly active impurity concentration and provides a method to determine th e phosphorus and boron concentration of the starting material. Our pre vious work has been extended with experiments using silicon with diffe rent original boron/phosphorus ratios, larger neutron fluences and to long term room temperature annealing. The donor removal rate of phosph orus was measured and the acceptor removal rate of boron evaluated. Ex tending our model, we propose that slow restoration of the damage indu ced boron interstitial back to its original substitutional state is re sponsible for the acceptor increase observed during long term annealin g. This model, which involves only the behavior of the known shallow d onors and accepters present in the starting material, fits our data an d the data of other experimenters without the need to invoke unidentif ied deep levels.