VACANCY-INITIATED LASER SPUTTERING FROM SEMICONDUCTOR SURFACES

We review recent experimental results of laser ablation of semiconduct ors and of submonolayer-sensitivity measurements of laser-pulse-induce d particle emissions from cleaned surfaces of GaP and GaAs. It is poin ted out that the particle emission yield below the ablation threshold decreases as irradiation is repeated, while that above the ablation th reshold increases, leading finally to ablation. The ablation processes are discussed on the basis of the experimental observation of the sub threshold emissions, which are ascribed to be due to breaking of bonds of weakly bonded atoms around adatom- and step-type defects on surfac es due to cascade electronic excitation. It is shown that existing exp erimental results on laser ablation can be explained on the basis of t he following mechanism: the ablation is initiated by laser-induced bon d breaking of weakly bonded atoms around the vacancies, which leads to evolution of vacancy clusters not only in the original topmost surfac e layer but also in the original inner layers. It is emphasized that o nly weakly bonded atoms around vacancies and vacancy clusters can be s puttered, but yet massive erosion of the surface is induced.