We report on a study of the adsorption and decomposition of arsine molecules on clean Si(100) 2 x 1 surfaces using photoemission and scanning tunneling microscopy (STM). Arsine decomposition depends on the substrate temperature and occurs in five regimes: (i) Below 100'C the arsine dissociatively adsorbs most likely into As-H and Si-H. At these temperatures there is negligible surface diffusion and the saturation arsenic coverage is 20% because the remaining Si sites do not have enough unoccupied near neighbors to provide four bonds for AsH3 adsorption. (ii) Between 100 'C and 400 'C the onset of surface diffusion increases the saturation coverage of As to 25% (i.e., one arsenic per four silicon atoms), As-As dimers form and coalesce into short chains. iii) Above 400 'C the hydrogen starts to desorb significantly thereby allowing larger As coverages. (iv) This process reaches an extremum at about 575'C where all hydrogen is desorbed resulting in nearly 100% As coverage. (v) Near 650'C the As desorption rate becomes significant. The STM images recorded in these regimes reveal a wide variety of surface structures which are due to different relative rates of AsH3 adsorption, H and As desorption, and H, As, and Si surface diffusion. The AsH3 adsorption and H and As desorption processes are discussed in the context of a kinetic model.

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