On the oxidation of silicon

Strained Silicon Photonics

A review of recent progress in the field of strained silicon photonics is presented. The application of strain to waveguide and photonic crystal structures can be used to alter the linear and nonlinear optical properties of these devices. Here, methods for the fabrication of strained devices are summarized and recent examples of linear and nonlinear optical devices are discussed. Furthermore, the relation between strain and the enhancement of the second order nonlinear susceptibility is investigated, which may enable the construction of optically active photonic devices made of silicon.

High Energy Transmission Electron Diffraction From Surface Monolayers During Silicon Oxidation

We have examined the behaviour of the clean Si (111) 7x7 reconstructed surface during exposure to oxygen over a range of temperature and pressure in a UHV transmission electron microscope (TEM). We present preliminary results of our study, discussing both the etching of the silicon surface by oxygen at elevated temperatures and lower oxygen pressures, and its roughening and oxidation at higher oxygen pressures. We achieve great sensitivity to the structure of the surface monolayers by analysing the diffraction of high energy electrons by these surface layers and can resolve the movement of individual monatomic surface steps. Our most dramatic result to date is a demonstation that surface steps do not move during the growth of native oxide.

Probe-Induced Native Oxide Decomposition and Localized Oxidation on 6H-SiC (0001) Surface: An Atomic Force Microscopy Investigation

We report, for the first time, the native oxide decomposition/etching and direct local oxide growth on 6H-SiC (0001) surface induced by atomic force microscopy (AFM). Surface native oxide was decomposed and assembled into protruded lines when the negatively biased AFM tip was scanned over surface areas. The mechanism of decomposition was found to be governed by the Fowler-Nordheim emission current enhanced by the negatively biased AFM tip. Direct oxide growth on the SiC surface was achieved when the AFM tip was immobilized and longer bias duration applied. In particular, the aspect ratio of oxide grown on SiC was found to be several times higher than that on the Si surface. The improved aspect ratio on SiC was attributed to the anisotropic OH(-) diffusion involved in vertical and lateral oxidation along the polar and nonpolar directions such as [0001] and [110] axis in SiC crystal. The electron transport in the above AFM grown oxide on SiC was further investigated by I-V characteristics. The dielectrical strength of AFM oxide against degradation and breakdown under electrical stressing was evaluated.

The compositions of barrier-type anodic films formed on aluminium in molybdate and tungstate electrolytes

During the formation of barrier-type anodic films on aluminium, low concen­ trations of electrolyte species, derived from electrolyte anions, are incorporated into the film. The incorporation process and the subsequent behaviour of the electrolyte species are of great relevance to understanding the mechanism of film formation and related phenomena, such as dielectric breakdown. This paper considers the incorporation of electrolyte species from molybdate and tungstate electrolytes. A capacitor model of the film is proposed to explain the resultant compositions of the films, which are dependent upon the concentration of ad­ sorbed anions at the film surface. Using Rutherford backscattering spectroscopy, it is shown that molybdenum and tungsten species are incorporated into films at similar, constant rates, but their distributions in the films differ owing to their different mobilities. Both species migrate as cations by a cooperative transport mechanism involving also Al 3+ and O 2- /0H _ ions. The compositions of the films depend upon the current density and the concentration, pH and temperature of the electrolyte although, for all conditions, only small amounts of electrolyte species are incorporated. The key role of the composition of the electrolyte at the film surface, which is significantly modified compared with the composition of the bulk electrolyte, is highlighted by preferential incorporation during film formation in the presence of both molybdate and tungstate ions.