Ultrafast carrier dynamics in nitrogen-implanted GaAs

The comparative analysis of the ultrafast carrier dynamics of pure GaAs and ion-implanted GaNAs is reported. Different nitrogen concentrations (up to 4%) are implanted and subsequently annealed by rapid thermal annealing (RTA). Damage analysis by channelling Rutherford backscattering (RBS) reveals that the annealing step improves the crystal quality, but does not restore the original quality. From photoreflectance measurements it is concluded that the highest achieved active nitrogen content in the implanted samples is 0.5% for an equivalent implantation dose of 1%. Carrier dynamics are investigated by one-colour pump-probe measurements covering an excitation wavelength range of 730-860 nm (1.7-1.44 eV) with femtosecond time resolution. Comparison with non-implanted GaAs indicates that the carrier relaxation in the implanted samples is dominated by traps associated with implantation damage.