Krishnan Raghavachari, Department of Chemistry, Indiana University Surface Chemistry of III-V Compound Semiconductors with Novel Cluster Models Krishnan Raghavachari, Department of Chemistry, Indiana University We have now developed cluster models that can accurately describe the structures and chemical reactions of adsorbates on indium phosphide surfaces. Our models include the proper balance between covalent and dative bonding in such compound semiconductors, and are large enough to incorporate the effects of neighboring dimers on the surface chemical reactions. Using our models, we have now investigated the growth mechanisms leading from (1) In-rich InP(001)-(2×4) surface to a P-rich (2×1) surface by reactions with PH3, and (2) H-stabilized P-rich (2×1) surface to In-rich surface by reactions with InH3. In both cases, the multi-step mechanistic steps involving precursor adsorption, dissociative chemisorption, and subsequent H2 elimination leading to intradimer and interdimer P–In–P or In–P–In linkages have been fully characterized using density functional theory (e.g., see the illustrated energy diagram). In conjunction with experimental observations, we have seen the presence of dative bonded PH3 at room temperature (Langmuir, 23, 2007, 10109, Surf. Sci. 600, 2006, 4888) in addition to the dissociated species including those with bridging hydrogen atoms. Our calculations accurately reproduce the temperature dependence of the observed infrared spectra including the desorption of the dative bonded species at high temperatures. We have seen interesting bond length-frequency correlations for P−H modes that may be useful in future studies. Using our cluster models, we are currently investigating the key steps involved in the formation of ordered ternary alloys. Additional work on passivation of InP surfaces is also ongoing.