Ion dose effect in subgap absorption spectra of defects in ion implanted GaAs and Si

Subgap optical absorption investigations have been used to study the influence of increasing ion dose on the properties of ion implanted layers of Si and GaAs. Beside the spectral region corresponding to the band edge region, a second region at lower energy, also exhibiting an exponential behavior but with a substantially larger value of the inverse logarithmic slope, has been observed in all the investigated samples. A common trend has been observed for ion implanted Si and GaAs in the dependence of the values of the lower energy region inverse logarithmic slope as a function of the implantation dose, and it depended on the presence or not of amorphous material in the implanted layer. The results are discussed in terms of a possible evolution of gap states responsible for the observed features.