DEFECT-INITIATED EMISSION OF GA ATOMS FROM THE GAAS (110) SURFACE-INDUCED BY PULSED-LASER IRRADIATION

We have measured the Ga0 emission yield from GaAs(110) surfaces for laser pulses of several photon energies near the band-gap energy 1.435 eV, ranging from 1.33 eV to 2.53 eV. Similarly to the case for emissions of Si atoms from Si(100) and of Ga atoms from GaP surfaces, we find that the Ga0 emission yield, under repeated irradiation with laser pulses at fluences smaller than that for ablating the surface, decreases from its initial value rapidly at first and then slowly, while repeated irradiation by laser pulses above the ablation threshold fluence increases the emission yield gradually. It is found that the Ga0 emission yield for laser pulses below the ablation threshold depends strongly on the photon energy hnu: the emission yield is relatively small for hnu < 1.39 eV (region I); the emission yield is essentially zero for 1.39 eV < hnu < 1.42 eV (region II); and the yield increases in a stepwise fashion when the photon energy increases across the transition energies involving surface states for hnu > 1.42 eV (region III). It is suggested that the emission for region I is induced by electronic excitation of defects on the surface, while that for region III is induced most dominantly by electronic transitions involving surface states. It is also found that the yield is a power function of the laser fluence with power indices 2-4 for the rapidly decaying component and 4-7 for the slowly decaying component, depending on the photon energy.