Desorption Induced by Electronic %excitation on Solid Surfaces

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Desorption and associated surface modification induced by laser irradiation are measured on the clean (1^^-1^^-1^^-) surfce of the compound semiconductor GaP. LEED observations of the structure change induced by irradiation with laser pulses near indirect band gap energy show that structure change induced under an experimental condition where the temperature rise is not significant. To make clear the nature of the electronic excitation leading to structure change, we measured the wave length dependence in the threshold laser fluence above which the clean (17x17) reconstructer surface structure change to (1x1) structrue. The results present clear evidence that the modification of clean surfaces occurs by surface electronic excitation near indirect band gap energy. The strong super linear dependence of the structure change and desorption on the laser fluence suggests that such atomic processes are induced by dense excitation of surface state.The desorption of Ga atoms were measured by means of resonant ionization spectroscopy using tunable dye laser. It shows that the threshold laser fluence for Ga desorption is just the same as that for the structure change by laser irradiation. This result does not give information on the mechanism for the desorption in addition to that from the measurement of the structure change. The small number of Ga atoms detected in desorption measurement, howerer, shows the possibility that the structure change mainly induced by the desorption of P atoms. It may suggest that the measurement of desorption of P atoms give more information on the mechanism of the desorption induced by electronic excitation.