Characterization of optically excited terahertz radiation from arsenic-ion-implanted GaAs

This work characterizes the optically excited terahertz (THz) radiation from arsenic-ion-implanted GaAs (GaAs:As⁺). We observed phase reversal in the emitted THz radiation field after the semi-insulating GaAs substrate was implanted. The peak amplitude of the emitted THz field increased from 25 mV/cm to 100 mV/cm after thermal annealing. This trend confirms the recovery in crystallinity of the as-implanted GaAs:As⁺ after annealing. By introducing a magnetic field, we observe a blue shift of the center frequency in the THz power spectrum from 0.57 THz for the as-implanted GaAs:As⁺ to 1 THz for furnace-annealed samples. Analysis of the blue-shifted spectra and unsymmetrical pulse shapes allows us to infer the increasing importance of the contribution of another unknown mechanism to the THz radiation from the GaAs:As⁺ samples after annealing. This is also explained satisfactorily by the crystallinity of the as-implanted and furnace-annealed GaAs:As⁺. Further, the effective carrier mobilities of as-implanted, rapid-thermal-annealed, and furnace-annealed GaAs:As⁺ are determined for the first time as 0.6, 2, and 15 cm²/Vs respectively according to the THz data.