NONTHERMAL LASER SPUTTERING FROM SOLID-SURFACES

Current understanding of the phenomena of laser-induced sputtering of nonthermal origin from semiconductors and insulators is reviewed. Experimental observations on laser sputtering of typical insulators and semiconductors are compared, emphasizing laser sputtering by photons having subgap energies. It is pointed out that the sputtering is not induced at low laser intensities in semiconductors, while sputtering in proportion to the density of excitation is observed for alkali halides. The difference is attributed to the absence and presence of self-trapping of excitons in two different types of materials. In high-sensitivity measurements of laser-induced sputtering from GaP surfaces, the change in the sputtering yield as the pulsed-laser irradiation is repeated on the same spot is correlated with the change in the defect concentrations on the surface top layer. Hence, high-sensitivity measurements of nonthermal laser-induced sputtering can be a useful technique for defect and impurity analysis on the top layer of the surface. Theoretical aspects of the laser-induced sputtering, including the nature of excitons, energy localization, bond breaking and dynamics of localisation are discussed. It is suggested that two-hole localisation on surface defect sites is the origin of sputtering in materials in which no self-trapping of excitons is induced.