Characterisation of ion-implantation-induced disorder in GaAs by EXAFS

The Ga and As local atomic environments in ion-implanted GaAs have been cha racterised with extended x-ray absorption fine structure spectroscopy. The accumulation of disorder prior to the onset of amorphisation has been inves tigated. For implantation at -188 degrees C, a heterogenous amorphisation p rocess was identified and an increase in bondlength and Debye-Waller factor and a decrease in first-shell coordination number were observed. Analysis of the EXAFS data using the cumulant method revealed a monotonic increase i n asymmetry in the interatomic distance distribution as a function of dose. Amorphised samples implanted to ion doses two orders of magnitude beyond t he amorphisation threshold have also been studied and the structural parame ters of amorphous GaAs were shown to be independent of implant conditions.