A rotatable mass spectrometer coupled with a Cl2 supersonic mol. beam scattering technique is used to examine the fundamental processes involved in thermal reaction and 355 nm laser-induced chem. etching of the GaAs(100) surface with a Cl2 mol. beam. The results of the thermal reaction of the GaAs/Cl2 system show that GaCl3 is the main product and its angular distribution can be fit with cos2.3 Q function. For the UV laser-induced reaction, the main reaction products are GaCl and Ga. The time-of-flight (TOF) spectra of these reaction products are measured as a function of the scattering angle, laser fluence and incident angle of the chlorine beam. The measured flux angular distribution and desorbing GaCl can be fit satisfactory with a function of (c1cosQ + c2cosnQ). It implies that the desorbing products are strongly collected at the direction of the surface normal, the kinetic energies of products are peaked around this direction. These phenomena can be interpreted in terms of post-desorption collisions.

Key words: GALLIUM ARSENIDE, REACTION KINETICS, SURFACES, MOLECULAR BEAM, ETCH, LASER INDUCTION, TIME OF FLIGHT SPECTRA