INVESTIGATION OF THE KINETICS OF DIGERMANE CHEMISORPTION AND REACTION-PRODUCT DESORPTION IN THIN-FILM GROWTH OF GERMANIUM

The kinetics of the elementary reaction steps in surface-limited thin film growth of germanium from digermane was investigated by utilizing surface differential reflectance. Separation of the elementary reactio n steps of chemisorption and reaction product desorption was achieved by using a pulsed molecular beam to modulate the digermane delivery to the heated substrate. Both elementary reaction steps were found to be single exponential first-order processes. The chemisorption reaction on Ge(100) was rapid (k1=500+/-50 s-1), and independent of the substra te temperature between 680 and 810 K. On the other hand the desorption step in the same substrate temperature range is strongly temperature dependent with an activation energy of 1.7+/-0.1 eV and a prefactor of 2 X 10(13+/-1) s-1. A simple kinetic model comprised of two opposing first-order elementary steps is found to be consistent with the experi mental results. It is concluded that the kinetic data are compatible w ith the pairing mechanism for molecular hydrogen desorption, but no (t hermal) decomposition mechanism of digermane is found to provide a uni que interpretation for the first-order adsorption kinetics.