Extended defects of ion-implanted GaAs

Ion-implantation-induced extended defect formation and annealing processes have been studied in GaAs. Mg, Be, Si, Ge, and Sn ions were implanted between 40 and 185 keV over the dose range of 1 X 10t3-1 X 1015/cm2. Furnace annealing after capping with S&N4 was performed between 700 and 900 “C for times between 5 min and 10 h. Plan-view and crosssectional transmission electron microscopy results were correlated with secondary-ionmass spectroscopy profiles. The results indicate subthreshold (type-I) defect formation occurs at a dose of 1 X 10i4/cm2 for high-energy, light (Mg, Be) ions but not for heavier ions (Si, Ge, Sn) at shallower projected ranges ( < 500 A). Si and Ge implants at a dose of 1 x 10’s/cm2 both show extended defect formation upon annealing that is believed to be precipitation related (type-V defects). For Si implants, these dislocation loops are eliminated after 10 h at 900 “C. Upon annealing 1 X 1015/cm2 Sn implants, unusual precipitate motion both toward the surface and into the crystal was observed. Type-II defects are observed but only in the as-implanted cross section. In addition, a layer of dislocatiqn loops formed at a depth much greater than the type-II defect layer. These defects appear to be a new type of defect possibly related to either the different binary recoil distributions of Ga and As or differences in vacancy and interstitial diffusivities. It is shown that, with modifications to account for the binary nature of the target, the classification scheme developed for extended defects in silicon can be applied to implantation of gallium arsenide.