PULSED-LASER SPUTTERING OF THE (100)GAALAS SURFACE

We have studied the pulsed laser sputtering of (100)Ga1-xAlxAs (x=0.54 5) surface with 337 nm photons, starting from the threshold for partic le emission (a few tens of mJ/cm(2)) up to about 300 mJ/cm(2). Atoms a nd molecules sputtered from the irradiated surface are detected, their relative number measured, and their time of flight determined using l aser resonant ionization mass spectrometry. After laser irradiation th e surface is examined by scanning electron microscopy and electron mic roprobe 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 pr ocess is quite similar to thermal evaporation. One observes preferenti al 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 str uctures. However, As preferential laser sputtering is rapidly counterb alanced by excess surface Ga and Al atoms leading to a stationery sput tering regime after a few thousand laser shots. A simple analytical mo del was developed which permits to define the conditions for such equi librium achievement. (C) 1996 American Institute of Physics.