Pulsed laser sputtering of the (100)GaAlAs surface

We have studied the pulsed laser sputtering of (100)Ga1-xAlxAs (x=0.545) surface with 337 nm photons, starting from the threshold for particle emission (a few tens of mJ/cm(2)) up to about 300 mJ/cm(2). Atoms and molecules sputtered from the irradiated surface are detected, their relative number measured, and their time of flight determined using laser resonant ionization mass spectrometry. After laser irradiation the surface is examined by scanning electron microscopy and electron microprobe analysis. From the shot number and the fluence dependencies of the sputtering yield, it is shown that two sputtering regimes exist. For low fluence (150 mJ/cm(2)), the sputtering results mainly from the absorption and excitation of defect sites. At higher fluences, the process is quite similar to thermal evaporation. One observes preferential emission of As in the form of As-2 molecules and the correlated Ga and Al enrichment of the surface with formation of GaAl microsized structures. However, As preferential laser sputtering is rapidly counterbalanced by excess surface Ga and Al atoms leading to a stationery sputtering regime after a few thousand laser shots. A simple analytical model was developed which permits to define the conditions for such equilibrium achievement. (C) 1996 American Institute of Physics.