Laser annealing effects in ion-implanted GaAs

The annealing behaviors in Si ion-implanted GaAs, using a Q-switch-pulsed ruby laser, are characterized by a strong dose dependence of implanted-impurity concentration thus electrically activated; carriers are generated or not, according as the dose ranges ≳ or ≲1014 cm−2. To characterize this impressive phenomenon, four factors are presented, which seem possible as its origin: (1) Cr segregation, (2) laser irradiation defects, (3) insufficient laser energy absorption, (4) residual implantation damage. A detailed study denies factors (1)–(3) to be its origin. Factor (4) is decisive; implantation damage remains after laser annealing, as the damage-related localized states whose typical density is roughly estimated to be ∼1018 cm−3 or somewhat less. This result gives a satisfactory explanation for the above phenomenon. The fact that implantation damage remains is, however, suggestive of an annealing mechanism differing from the normal melting.