Effects of structural defects on the activation of sulfur donors in GaN xAs 1- x formed by N implantation

The effects of structural defects on the electrical activity of S-doped GaN _xAs _{1- x} layers formed by S and N co-implantation in GaAs are reported. S and N ions were implanted to the depth of about 0.4 μm. Electrochemical capacitance voltage measurements on samples annealed at 945°C for 10 s show that in a thin (<0.1 μm) surface layer the concentration of active shallow donors is almost an order of magnitude larger in S and N co-implanted samples than in samples implanted with S alone. The activation efficiency of S donors also shows a broad minimum at a depth of about 0.2 μm below the surface. The results of these electrical measurements are correlated with the distribution of structural defects revealed by transmission electron microscopy (TEM). The TEM micrographs show that in addition to a band of dislocation loops commonly found in ion implanted GaAs, an additional band of small voids is observed in samples co-implanted with S and N. The location of this band correlates well with the region of reduced electrical activation of S donors, suggesting that the formation of the voids through N accumulation results in a lower concentration of “active”, substitutional N atoms.