On the kinetics of the exchange of hydrogen between hydrogen–boron pairs and hydrogen dimers in crystalline silicon

Silicon samples after fast-firing with a hydrogen-rich silicon nitride layer on their surfaces can contain high concentrations of hydrogen (up to 6 × 1015 cm−3 in this study). Directly after fast-firing, this hydrogen is mostly present in a neutral dimeric state. Subsequent dark annealing applied in a temperature range between 140 and 175 °C leads to a conversion of dimers into HB pairs, which means that a significant number of boron acceptors are electrically inactive. The concentration of inactive boron, the hydrogen–boron (HB) pair concentration [HB], can thus be determined by measuring the change in specific resistivity before and after annealing. In our study, after the initial anneal for HB pair formation, the same samples are subsequently annealed at stepwise increasing higher temperatures, which leads to a partial backward conversion of HB pairs into neutral hydrogen dimers. This is indicated by a gradual reduction of the resistivity upon increasing the annealing temperature. By measuring the transient curves [HB](t) during each temperature step on samples with different boron content, we extract the parameters for the exchange between the HB pairs and the hydrogen dimers within the framework of our presented physical model. Apart from the backward formation of hydrogen dimers, from HB pairs upon increasing temperature, prolonged annealing at the same temperature leads to a transition of HB pairs into a more stable form of hydrogen dimers, compared to the initial form after fast-firing. This transition is also included in our proposed defect model.