THE PHOTOINDUCED REACTION OF DIGERMANE WITH THE SI(100)(2 X 1)-D SURFACE

Photo-induced surface reactions brought about by photolysis of adsorbed digermane on the Si(100)(2 X 1):D surface have been investigated under ultrahigh vacuum conditions using Auger electron spectroscopy and temperature programmed desorption. On the monodeuterated Si(100)(2 X 1):D surface, no spontaneous thermal reaction of digermane is observed, due to the termination of the dangling bonds with D atoms. Molecular Ge2H6, weakly adsorbed on Si(100)(2 X 1):D at 120 K, dissociates upon UV irradiation, leading to the incorporation of Ge atoms and the adsorption of H atoms on the surface. The appearance of a new low temperature alpha desorption state for hydrogen (deuterium) desorption near 580 K is further evidence for Ge deposition and the photo-induced decomposition of physi-adsorbed Ge2H6. The observation of alpha-HD and alpha-D2 desorption indicates that the photoreaction intermediate inserts into the surface Si-D bond to produce a Ge-D bond. Studies of the thermal reaction of Ge2H6 with partially deuterated (THETA(D) < 1.0) Si(100) surfaces model the chemistry expected for a germyl radical intermediate, and illustrate that the germyl radical does not give rise to the observed surface photochemistry. The enhanced production of Ge trihydride (deuteride) species with increasing UV exposure, as measured by the GeHxD4-x desorption yield, coupled with the observation of Ge-D bond formation, reveals that the photo-induced Ge2H6 surface reaction is dominated by an insertion reaction into surface hydride (deuteride) bonds by the photo-generated species germylene.