Brian Bech Nielsen

Si-H stretch modes of hydrogen-vacancy defects in silicon

Abstract The Si H stretch modes in proton-implanted crystalline silicon have been studied by FTIR spectroscopy. From the annealing behaviour and dose dependence of the stretch-mode intensities, it is found that one complex gives rise to modes at 2121 and 2144 cm −1 , a second to modes at 2166 and 2191 cm −1 , and a third to a single mode at 2222 cm −1 . The isotope shifts of these centres have been obtained from measurements on samples implanted with protons and deuterons. Moreover, the symmetries of the centres have been determined from uniaxial stress measurements. We assign the 2121 and 2144 cm −1 modes to VH 2 , the 2166 and 2191 cm −1 modes to VH 3 , and the 2222 cm −1 mode to VH 4 . Another mode at 2068 cm −1 is tentatively ascribed to VH. The Si H and Si D stretch modes of VH n D m ( n + m ≤ 4) have been calculated with a simple model which has been used to fit all the experimental frequencies. The agreement between fitted and observed frequcies is excellent.

Near-infrared–ultraviolet absorption cross sections for Ge nanocrystals in SiO2 thin films: Effects of shape and layer structure

Measured absolute optical absorption cross sections of 2–6 nm Ge nanocrystals embedded in SiO2 in the near-infrared–ultraviolet spectral range are reported. Thin layers of Ge sandwiched between SiO2 layers were prepared in a multilayered configuration, which upon heat treatment at 800 °C led to multilayers of Ge nanocrystals with a narrow size distribution. Four samples with different nanocrystal average sizes were prepared by this technique. In addition, samples containing Ge nanocrystals randomly distributed in SiO2 films were also prepared in order to clarify the effects of the multilayer configuration on the optical properties. The size distribution and density of the nanocrystals were obtained from transmission electron microscopy investigations and Rutherford backscattering spectrometry measurements. In combination with this structural information the nanocrystal absorption cross sections were obtained from optical transmission measurements, which were corrected for thin film interference effects by...

Line spectrum of the interstitial iron donor in silicon

Photothermal ionization spectroscopy and infrared transmission measurements have been carried out on iron‐doped silicon. A series of sharp lines in the range from 6100 to 6400 cm−1 was observed with both techniques. Photoionization cross‐section spectra were determined by photothermal ionization spectroscopy and photoelectron paramagnetic resonance, and it is concluded that the lines originate from electronic transitions to excited shallow donor states at the interstitial iron impurity in the neutral charge state Fe0i. The lines and the Fe0i ‐related electron paramagnetic resonance signal annealed out together at approximately 170 °C. The line spectra are analyzed in terms of three overlapping donor series and the origins of these are discussed.

Ion beam detection of the austenitic-martensitic phase transformation of single crystal stainless steel

Abstract The austenitic-martensitic phase transformation in single crystal stainless steel of composition 70% Fe, Cr, 13% Ni has been observed by ion beam analysis techniques to occur at 175 K.

Passivation of Ge nanocrystals in SiO2

Nanocrystals have attracted considerable attention in recent years because of their potential applications as a light source in Si technology. From theory Ge nanocrystals are expected to have better luminescence properties than Si nanocrystals. In this study we have compared Ge nanocrystals produced both in PE-CVD deposited and magnetron sputtered SiO2 doped with Ge during deposition to concentrations between 3-9 at.%, followed by high temperature treatment at temperatures between 600 and 1100°C. The nanocrystals were structurally characterized by Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR). The interface of the nanocrystals was passivated by use of alnealing, while the effect of the passivation was monitored by photoluminescence (PL)

Host Isotope Effect on the Local Vibration Modes of VH2 and VOH2 Defects in Isotopically Enriched 28Si, 29Si and 30Si Single Crystals

Local vibrational modes of a vacancy with two hydrogen atoms (VH2) and of a vacancy with one oxygen and two-hydrogen atoms (VOH2) in silicon have been investigated using isotopically enriched 28Si, 29Si, and 30Si single crystals. Infrared absorption spectroscopy revealed shifts in the Si–H stretch frequencies of the two defects when the mass of the silicon host atoms was changed. The observed stretch frequencies can for each defect be accounted for with a simple vibrational model based on two coupled Morse oscillators. The anharmonic contribution to the local vibrational mode frequencies of these two defects is evaluated.

Raman Investigation of the Localized Vibrational Mode of Carbon in Strain-Relaxed Si1-xGex:C

The localized vibrational mode (LVM) of carbon in strain-relaxed Si1-xGex:C samples with x=0, 0.05, 0.35, and 0.5 have been investigated by Raman spectroscopy at room- and liquid-nitrogen-temperatures. The position of the Raman peaks due to LVM of carbon shifts linearly to lower frequencies with increasing x from 0 to 0.5. The LVM frequencies of carbon obtained by Raman measurement agree very well with those determined by Hoffmann et al. in infrared (IR) absorption recently.