SOFT LASER SPUTTERING OF THE GAALAS (100) SURFACE

We have studied the soft laser sputtering of (100)GaAlAs with 337 nm p hotons, starting from the threshold for particle emission (a few tens mJ/cm(2)) up to about 300 mJ/cm(2). Atoms and molecules sputtered from the irradiated surface are detected, their relative number measured a nd their time-of-flight determined using laser resonant ionisation mas s spectrometry (RIMS). After laser irradiation the surface is examined by scanning electron microscopy (SEM) and electron microprobe analysi s (EMA). From the shot number and the fluence dependencies of the sput tering yield, it is shown that two sputtering regimes exist. For low f luence (<150 mJ/cm(2)), the sputtering results mainly from the absorpt ion and excitation of defect sites. At higher fluences the process is similar to thermal evaporation. One observes preferential emission of As in the form of As-2 molecules and the correlated Ga and Al-enrichme nt of the surface with formation of GaAl micron-sized structures. Howe ver, As preferential laser sputtering is rapidly counterbalanced by ex cess surface Ga and Al atoms leading to a stationary sputtering regime after a few thousand laser shots.