Atomic layer deposition (ALD) of alumina (Al2O3) using water and aluminum trichloride (AlCl3) is studied using density functional theory (DFT). The atomistic mechanisms of the two deposition half-cycles on Al2O3−OH* and Al2O3−Cl* surface sites include the formation of stable intermediates and result in high barriers for HCl formation. Increasing the temperature reduces the stability of the intermediates but also increases the desorption rate of adsorbed precursors. Both half-reactions are qualitatively similar to the corresponding reactions of ALD of HfO2 and ZrO2 from H2O and HfCl4 and ZrCl4, respectively, but differ significantly from the reactions of ALD of Al2O3 from Al(CH3)3 and H2O. Although the high electronegativity of Cl increases the stability of the dative-bonded trapped intermediates in the Zr and Hf chloride cases, the inductive effect is stronger for AlCl3, increasing the stability of adsorbed AlCl3 by 29 kcal/mol relative to the adsorption energy of Al(CH3)3. Furthermore, the ligand-exchange barrier is 26 kcal/mol higher for AlCl3 than for Al(CH3)3, thus reducing the reaction kinetics and increasing the ALD temperature for the AlCl3/H2O system. We have also found a new reaction pathway which involves ligand-exchange without metal deposition which we call nongrowth ligand-exchange. This pathway is more competitive in ALD using AlCl3 as the metal precursor than when using Al(CH3)3 and reduces the ALD growth rate. These results provide additional physical insight into the nature of these reaction mechanisms and demonstrate that the Cl ligands have a larger impact on the reaction energetics than the metal atom for the ALD of these high-κ oxides.

Atomic nitrogen on the Si(100)-(2 × 1) surface is investigated using B3LYP density functional theory to study the incorporation of nitrogen atom into the silicon surface during growth of nitride films on silicon. Several possible structures for nitrogen on the Si(100)-(2 × 1) surface are investigated, including N bridgebonded into the Si-Si dimer, N bridge-bonded into the Si-Si back-bond, and N inserted by forming three bonds with three Si atoms. Furthermore, the energetics and reaction mechanisms leading to these structures are also calculated. We find that the structure with nitrogen atom bridge-bonded into the Si-Si dimer to be the most thermodynamically stable, with an adsorption energy of 105 kcal/mol and an insertion barrier of 29 kcal/mol. Insertion into the Si-Si back-bond, however has the lowest activation barrier of 11 kcal/mol, although its adsorption energy is 13 kcal/mol lower than insertion into the Si-Si dimer. The third configuration investigated with N forming three bonds with Si atoms has a relatively high activation barrier of 35 kcal/mol and an adsorption energy of 95 kcal/mol. In addition, the formation of this structure "consumes" three Si atoms. Hence, at high nitrogen pressure, this structure is expected to be less dominant than those with N inserted into the Si-Si bonds, which only consume two Si atoms.

We have numerically studied the band structure and the spin polarization effect in a periodic one-dimensional array of quantum point contacts (QPCs) formed in a two-dimensional electron gas in a plane-layered semiconductor system. In this study we used a self-consistent model developed within the framework of the Kohn–Sham local spin-density formalism. We have found that the band structure contains a mixture of flat and dispersed bands, and the role of transverse modes in the formation of such a band structure has been clearly demonstrated. We have also shown that spin polarization occurs mainly in the regions occupied by the QPCs and that it is qualitatively similar to the spin polarization in a single QPC.