The electrical activity of phosphorus channelled into silicon

The electrical activity of phosphorus ions, implanted at energies between 40 and 400 keV along the 〈110〉 axis of silicon crystals, has been measured as a function of depth, following a 700°C anneal. The electrical activity, determined by differential electrical sheet conductivity measurements combined with anodic stripping, was found to be close to 100 per cent in both pulled and float-zoned material. In some cases it was possible to compare carrier concentration and impurity ion distributions within the same specimen, implanted with a mixed dose of P31 and Pa32. By radioactive tracer techniques it has been shown that de-channelling of phosphorus ions is significantly greater in certain dislocation-free crystals than in other, dislocated silicon crystals. Scanning X-ray diffractometer measurements reveal considerably more lattice strain in the former. It is proposed that both effects may arise from vacancy clustering, together with associated decoration by impurity atoms, as a result of the absence of sinks provided by a few dislocations. The degree of channelling of P32 in epitaxially-grown 〈111〉 silicon has been found to exceed that in high-quality bulk-grown crystals. The consequences of this observation, combined with the high electrical activity of channelled phosphorus, are considered briefly.