Band bending at the Si(1 1 1)–SiO2 interface induced by low-energy ion bombardment

Experiments employing photoreflectance spectroscopy have uncovered band bending due to electrically active defects at the Si(1 1 1)–SiO₂ interface after sub-keV Ar⁺ ion bombardment. The band bending of about 0.5 eV resembles that for Si(1 0 0)–SiO₂, and both interfaces exhibit two kinetic regimes for the evolution of band bending upon annealing due to defects healing. The healing takes place about an order of magnitude more quickly at the (1 1 1) interface, however, probably because of less fully saturated bonding and higher compressive stress.     

Temperature-dependent energy thresholds for ion-stimulated defect formation in solids

Recent simulations and experiments have hinted that the solid temperature may affect the dynamics of defect formation when the energies of bombarding ions fall below about 100 eV. The present work offers direct experimental confirmation of this phenomenon through measurements of the energy thresholds for ion-enhanced surface diffusion of indium on silicon and germanium, where transport rates depend upon surface defect formation. Such temperature-dependent energy thresholds may offer a new means for modulating sputtering and defect formation in a variety of ion processing applications.     

Differential-conversion temperature programmed desorption: a new method for obtaining bimolecular surface rate constants

For bimolecular surface reactions, temperature programmed desorption (TPD) cannot be used efficiently to detect the product if either of the reactants desorbs before the product. A modification of TPD (differential-conversion TPD, or DCTPD) that circumvents this problem is described in this paper. The reactant desorbing at high temperature is first adsorbed as in normal TPD. The surface is then exposed to a continuous flux of the other reactant, and the rate of product desorption is monitored at the same time. The flux is kept so low that the coverage of the reactant first adsorbed scarcely changes. The rate constant is then determined using this measured coverage and that calculated for the impinging species from its previously-determined adsorption/desorption kinetics. A formalism is also developed for cases in which a continuum of related pathways with a distribution of activation energies is present. Experimental application of DCTPD is demonstrated in the particular case of HCl production from SiH₄ and TiCl₄ on TiSi₂.     

Control of defect concentrations within a semiconductor through adsorption

The technologically useful properties of a crystalline solid depend upon the concentration of defects it contains. Here we show that defect concentrations as deep as 0.5 microm within a semiconductor can be profoundly influenced by gas adsorption. Self-diffusion rates within silicon show that nitrogen atoms adsorbed at less than 1% of a monolayer lead to defect concentrations that vary controllably over several orders of magnitude. The results show that previous measurements of diffusion and defect thermodynamics in semiconductors may have suffered from neglect of adsorption effects.     

Structure and mobility on amorphous silicon surfaces

The structure and dynamics of amorphous surfaces are poorly understood. The present work develops methods employing classical molecular dynamics (MD) simulations to elucidate these phenomena on amorphous silicon. Careful relaxation of the initial ensemble and taking account of exchange with the bulk yield surface diffusion coefficients in good agreement with experiment. Randomly oriented dimer pairs dominate the surface structure. Diffusion proceeds by several pathways, which all differ in basic character from those typically observed on crystalline silicon. The primary pathways involve single atoms and dimer pairs, which typically move only one or two atomic diameters before reincorporating into the surface. Frequent vertical migration takes place between the first two atomic layers.     

Vacancy charging on Si(1 1 1)-(7 × 7) investigated by density functional theory

The structure and energetics of charged vacancies on Si(1 1 1)-(7 × 7) are investigated using density functional theory calculations supplemented by estimates of ionization entropy. The calculations predict multiple possible charge states for the unfaulted edge vacancy in the adatom layer, although the −2 state is most stable on real Si(1 1 1) surfaces for which the Fermi level lies near the middle of the band gap.     

Structural and magnetic properties of Mn-doped anatase TiO<Subscript>2</Subscript> films synthesized by atomic layer deposition

Mn-doped anatase TiO₂ (Mn: 1.2, 2.4 at%) thin films were grown on Si(100) via atomic layer deposition (ALD). The synthesis utilized Ti(OCH(CH₃)₂)₄ and H₂O as ALD precursors and Mn(DPM)₃ as a dopant source. X-ray photoelectron spectroscopy measurements indicate that Mn is successfully doped in the TiO₂ matrix and reveal information about film composition and elemental chemical states. Microstructure, crystallinity, and density were investigated with scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. All ALD-synthesized films exhibited room-temperature ferromagnetism; the microstructure, density, and magnetic field-dependent magnetization of the TiO₂ varied with the concentration of Mn. ALD permits precise composition and thickness control, and much higher process throughput compared to alternative techniques.