EVIDENCE FOR REVERSIBLE DISSOCIATIVE ADSORPTION IN THE REACTION OF MOLECULAR CHLORINE WITH GALLIUM-ARSENIDE

The reaction of molecular chlorine with the (100) face of a gallium arsenide crystal has been studied at pressures of Cl-2 between 0.10 and 9.0 Torr and in the temperature range from 90 to 110 degrees C. In contrast to an earlier report, the etch rate was found to be half order with respect to Cl-2. The similarity of these results to those obtained for the reaction of molecular chlorine and bromine with silicon points to a mechanism in which the gaseous halogen molecule is first physisorbed on the semiconductor surface and then dissociates into chemisorbed atoms. The data indicate that both steps occur reversibly at higher pressures, where the composite half-order rate constant can be represented by the Arrhenius equation: k(1/2) = 10(13.6+/-2.6) mu m min(-1) Torr(-1/2) e(-(100+/-19kJ) (mol-1/RT)) At low pressures the first-order rate constant is given by the equation: k(1) = 10(10.4+/-2.3) mu m min(-1) Torr(-1) e(-(76+/-16kJ) (mol-1/RT)