ANGLE-RESOLVED SUPERSONIC MOLECULAR-BEAM STUDY OF THE CL2/GAAS(110) THERMAL ETCHING REACTION

Angle-resolved supersonic molecular beam scattering and time-of-flight techniques (TOF) are used to probe the dynamics of the Cl2/GaAs{110} thermal etching reaction. TOF spectra are recorded for the unreacted Cl2 and the GaCl3 reaction product as a function of incident translational energy and surface temperature at various final scattering angles. Our results show that the reaction mechanism is precursor mediated. The weakly bound molecular (Cl2)ads species is a key reaction intermediate through which subsequent reaction steps occur. The reaction probability, determined by angle integration of the unreacted Cl2 flux, increases with surface temperature (T(s)) reaching a plateau and decreasing slightly between T(s) approximately 425 K and 525 K before increasing sharply again beyond 525 K. This trend is nearly independent of incident kinetic energy. Detailed analysis of the TOF spectra reveal that the dynamical origin of this effect is due in part to a change in the reaction kinetics in which Cl2 desorption competes with product formation. The insights gained in this study are used to formulate plausible explanations for several discrepancies existing in the literature concerning the temperature dependence of the etch rate and of the high temperature product distribution.