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Surface modifications induced to GaSb single crystals by pulsed U.V. laser annealing (PLA) in ultra-high-vacuum have been studied. The (111) surfaces of GaSb single crystals were prepared by a mechanical and chemical etching before introducing into vacuum. The samples were subsequently exposed in vacuum to the U.V. radiation (193 nm) of an high power excimer laser. The analysis by Auger electron spectroscopy performed in situ shows that an atomically clean surface (free of native oxides and of carbon pollution) can be achieved by PLA. The effects of the Energy Density (ED) and of the repetition of the PLA are addressed. Superficial topology changes observed in situ by low resolution scanning electron microscopy, and later by optical microscopy, are described too. From our observations we conclude that She antimony oxides begin to decompose noticely when the surface is irradiated with 50 mJ/cm2 laser pulses. Their evaporation explains the onset of the sharp chemical reduction observed at higher fluences. We propose that superficial melting of the GaSb single crystal starts as soon as the laser beam ED reaches 100 mJ/cm . Beyond this fluence the superficial chemical reduction is completed not only by evaporation, but also : - first : by thermal stress induced fracture of the gallium oxide layer and its ejection due to the strong evaporation from the substrate, and, - second : by the gallium oxide dissolution into the melt. The amount of antimony segregated on ple surface becomes important when the surface melts deeply (i.e. at ED superior of 150 mJ/cm2).
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