It was demonstrated that the depth distributions of defects in MeV-implanted n-type or p-type crystalline material were markedly affected by the impurity content of the material. Samples with various concentrations of P or B dopants, and of intrinsic contaminants such as C and O, were implanted with 1 or 2MeV He ions to fluences that ranged from 2.5 x 108 to 1013/cm2. By using deep-level transient spectroscopy and spreading resistance measurements, the concentrations and depth distributions of the defects were determined. It was found that less than 4% of the defects that were generated escaped recombination and became stored in electrically active stable room-temperature defect clusters such as di-vacancies and C-O pairs. It was noted that, when the concentrations of these defects were much smaller than the doping level, their profiles reflected the initial defect distribution; as calculated by using a Monte Carlo technique. It was noted that the profile exhibited a maximum at the same depth that was predicted by an analysis of ion transport. Its width depended strongly upon the impurity content of the substrate. This width could be as large as 2 when implantation was carried out on a lightly-doped pure epitaxial substrate, and reverted to the predicted value (about 0.5) upon increasing the concentrations of dopants and intrinsic contaminants which acted as traps for the diffusing point defects. Broadening of the concentration profiles was shown to be unavoidable at high implantation fluences, when most of the traps were full and were unable to impede the free migration of newly generated defects. By comparing the defect distributions in n-type and p-type samples, the spatial separation between vacancy-type and interstitial-type defects, which resulted from ion momentum transfer, was deduced. The results were explained in terms of trap-limited diffusion of the defects that were generated by implantation. These effects were observed only in the case of a light ion such as He, since direct defect clustering within the diluted collision cascades was expected to be greatly inhibited.

S.Coffa, V.Privitera, F.Priolo, S.Libertino, G.Mannino: Journal of Applied Physics, 1997, 81[4], 1639-44