Electron trapping levels in silicon dioxide thermally grown on silicon

Photocurrents associated with optical release of photoinjected electrons trapped in thin films of amorphous silicon dioxide have been studied. Temporal and spectral variation of the photocurrents were examined in detail: the effects on spectrally resolved response caused by variations in applied electrical field, wavelength sweep rate, and optical belaching are reported. All measurements were made on metal-oxide-semiconductor capacitors. The experiments were interpreted in terms of a straightforward model of optical excitation and transport of electrons out of localized energy levels in the silicon dioxide band gap. Semi-quantitative analysis indicated that a distribution of states peaked approximately 2·1 eV below the conduction band edge was associated with an electron trapping center distributed rather uniformly throughout the oxide film. In the wet thermal oxide specimens examined, the average density of trapping centers was greater than 10¹⁴ cm⁻³. A time-stable spread in energy of approximately 0·5 eV was measured, and was attributed to local disorder in the amorphous insulator. The existence of an optically inactive charge distribution in the oxide films, with bulk average density greater than 10¹⁵ cm⁻³, was indicated by collected charge vs. applied field data.     

Electron dynamics at surfaces

The physics of electron dynamics at surfaces and interfaces encompasses a rich variety of processes ranging from electron scattering and diffusion to electron-hole recombination and surface state and defect trapping. This review includes an overview of many of these important interactions and a detailed discussion of the experimental approaches used to study them. Particular attention is given to the surface-sensitive technique of angle-resolved photoemission carried out with nanosecond, picosecond and femtosecond laser sources which have revealed new insights into the modes of dynamical electronic properties at surfaces. A range of experiments carried out on semiconductor and metal surfaces will be described.     

Infrared spectroscopy of hydrogen on silicon surfaces

This paper is a review of infrared studies of hydrogen-terminated silicon surfaces. Emphasis is given to the ideally H-terminated Si(1 1 1) surface, prepared by wet chemical techniques, because detailed information can be obtained concerning the Si-H stretching vibration, such as its precise frequency and effective charge, its lifetime and the nature of its anharmonic coupling to the SiH bending mode and to the substrate surface phonons. Comparison of this nearly ideal surface with the H-exposed Si(1 1 1)7 × 7, Si(1 1 1)2 × 1 and Si(1 0 0)2 × 1 gives some insight into the effects of reconstruction and strain on the Si-H vibrational spectrum.     

First-principles investigation of functionalization-defects on silicon surfaces

We present a theoretical study of chemisorption of CHC-CH₂-COOH molecules on the H:Si(1 0 0) surface. We perform simulations for different chemisorbed configurations, attained by reactions through the alkyne tail. We use the periodic slab approximation for the extended surface, within ab initio density functional theory, and analyse results from several different approaches. We conclude that structures composed of single Si-C bridges are very stable, while a previously proposed structure, with a double Si-C-Si bridge, should be metastable on the flat surface, and introduce electron and hole traps in the Si band gap.     

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.     

Femtosecond nanostructuring of silicon surfaces

Nanostructures were formed upon the irradiation of single-crystal silicon surfaces with femtosecond laser pulses. These nanostructures were detected using scanning electron microscopy, Raman spectroscopy, and a photoluminescence technique.     

Electron escape depth in silicon

The ESCA electron escape depth in silicon is determined from the peak areas in the electron spectra from evaporated thin films. For electron energies in the region 320 eV to 3.6 keV values from 13 to 83 Å are obtained. The escape depth in silicon dioxide is determined for the energies 1.6 and 3.6 keV. Binding energies and Auger energies are determined in silicon and silicon oxides.     

Field evaporation of silicon surfaces

Quantitative measurements on field evaporation of Si(111) surfaces in hydrogen imaging gas have been carried out by field ion microscopy. The field evaporation rate is found to increase exponentially with increase of the reciprocal of tip temperature in the range 80–103 K. The evaporation field strength increases with increase of tip temperature in the investigated range, 80–300 K. Within the applied pressure range, 5× 10^?6 to 2 × 10^?4 Torr of hydrogen gas, the evaporation rate linearly increases with the gas pressure. Similar effects of temperature and gas pressure on field evaporation of Si(111) surfaces have been observed also in silane imaging gas. A model, based on a field-induced formation of surface hydrides as a rate-determining step, is proposed, which accounts for all the experimental results of the field evaporation process.     

Electron irradiation effects on muonium states in silicon

Normal and anomalous muonium were studied in electron irradiated silicon. We found that the two muonium states behave very differently: For normal muonium, the relaxation rate increases if the sample is irradiated whereas it decreases for anomalous muonium. Possible explanations for these processes are discussed.     

Constructing self-organized structures on silicon and sapphire surfaces

We investigated methods to fabricate distinctive structures on silicon and sapphire substrates to grow a carbon nanotube (CNT) network using a solution from the Belousov-Zhabotinsky (BZ) reaction. The BZ reaction is a chemical system where chemical reactions and material diffusion coexist in a nonequilibrium state and generate spatiotemporal patterns in a petri dish. Precipitates from the reaction should also produce distinctive structures after being piled on the substrates. The structures have metal particles that act as catalysts for growing CNTs or quantum dots of nanodot devices. Therefore, such structures should be suitable to fabricate three-dimensional CNT networks or nanodot devices. To confirm this, we investigated the fabrication of distinctive structure using a BZ reaction solution. Results indicated that the BZ reaction solution produced interesting structures on the substrates. Moreover, we confirmed that the shape of the structure changed when the substrate used was changed. We believe that the developed methods are suitable to fabricate nanodevices, especially CNT network devices.     

Electron microscopy of growth surfaces on epitaxial films

It has been found that the final stage in the growth of an epitaxial film is decoration of the surface; to obtain objective information on the growth relief, it is necessary to examine at least two successive carbon replicas.     

Electron beam effects on oxygen exposed aluminum surfaces

The damaging effects of electron beams during the acquisition of electron spectra have long been an obstacle in surface analysis. In order to understand the physico-chemical processes which take place under electron irradiation in an AlO system, we have carried out an experiment in which artifices, such as heating, charging, and gas contamination, were absent. We have observed with Auger Electron Spectra increases of the oxidation extent and the oxygen concentration on an oxygen exposed (111) textured polycrystalline surface under electron irradiation (5 keV, 9 × 10^?5 A/cm²). These increases were not observed on a clean surface, and were very feeble on a (100) single crystal surface. The increase of oxygen concentration was independent of residual gas pressure (3 × 10^?9 to 6 × 10^?10 Torr) and its composition; and therefore cannot be explained by gas contamination during the experimental period (about 70 min). We attribute the increase of oxidation degree to the transition of chemisorbed oxygen atoms into oxide through direct momentum transfer from the incident electrons. We suggest that the increase of oxygen within the irradiated area is due to the surface diffusion of chemisorbed oxygen atoms from outside the irradiated area. These oxygen atoms are excited by the electrons scattered from the vacuum chamber walls and gain energy through Franck-Condon type mechanism. The absence of chemisorbed oxygen atoms on (100) surface explains the near absence of these increases on this surface.