The Decomposition of Hydrides from Silicon and Germanium(x) SILICON(1-X) Surfaces: AN Examination of the Mechanisms Involved during Hydrogen Desorption.

The decomposition pathways of various hydrides from the surfaces of single crystalline silicon have been examined under ultrahigh vacuum conditions. Temperature programmed desorption has been employed to monitor the different reaction by-products resulting from the decomposition of these surface hydrides. Adsorption of hydrogen at 650K leads to the creation of monohydrides exclusively which in-turn produces only molecular hydrogen during desorption. At 400K, adsorption leads to creation of monohydrides and dihydrides whereas adsorption at 300K and 140K can lead to the additional creation of the trihydride. Surface erosion is initiated with the trihydride, leading to a generally disordered surface. The trihydride may either decompose back into a pair of mono- and dihydrides or desorb from the surface upon temperature programming. Mass spectrometry fragmentation patterns of the 635K desorption feature suggest silyl desorbs alongside silane. The stability of the trihydride with respect to dangling bonds and substrate temperatures is also explored. Disilane dissociatively chemisorbs onto Si(100) creating a mixture of mono- and dihydrides. Saturation of a partially deuterated Si(100)-2x1:D surface with disilane results in the production of H_2, HD, and D_2 during desorption. The observation of an HD-beta_2 desorption state suggests that the dihydride may decompose intermolecularly between a dimerized monodeuteride and a free-standing dihydride. Significant alterations to the hydrogen desorption profile are made with the inclusion of small quantities of germanium onto the Si(100) surface. The desorption maxima are increasingly lowered with added germanium content, implying that the activation energy required for desorption is also lowered. This phenomenon is also observed for the (111) surface. The observation of this trend from two vastly dissimilar surface structures would suggest that the bonding between silicon and hydrogen is weakened with the introduction of germanium. Due to the difference in mobility of hydrogen on these two surfaces, it is unlikely that germanium serves as the desorption center for hydrogen. Thus, we conclude that germanium perturbs the silicon-hydrogen bonding interaction through a long range electronic effect.