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The photoluminescence of electrochemically etched silicon under excitation in the wavelength range from 325 to 514 nm is described by a single energy gap (of order of 1.9 eV). The Raman spectra can be explained by a Gaussian phonon confinement to a geometrical structure size of about 3 nm. In addition, the novel method of spark erosion for a non-liquid preparation of light-emitting silicon has been used, and it is shown that the light emission spectrum, apart from its overall intensity, is independent of environment gas species (N 2 , O 2 or H 2 ). In areas of higher electric field strength, presumably leading to a smaller effective size, a blue shift is observed in all these cases. This appears to rule out any siloxene-derivate models and suggests a quantum confinement as the basic phenomenon.

Studies of the oxygen isotope exchange kinetics in 18 O substituted YBa 2 Cu 3 O 7 (123) have been performed. As a weight decrease is observed during the 18 O→ 16 O exchange, high resolution thermogravimetric measurements (both isothermal and non-isothermal) were used to investigate the kinetics. The exchange process takes place at relatively low temperatures, 225–430°C, and was found to be non-isokinetic in this temperature range. Two ranges with different activation energies have been found: (1) 1.88 eV both in the ranges 433-398°C (total exchange of 18 O in the planes+apex+chains) and 353-307°C (exchange mainly in apex+chains) but with different pre-exponential factors and (2) 0.71 eV at t

Samples of porous silicon, produced electrochemically with a spatially varying current density, have have studied by Raman scattering, by spectral photoluminescence (PL) and by photoluminescence topography. The PL maximum observed at about 1.7 eV shifts to higher energies (2.0 eV) for the strongest structuring, where the highest PL is also found. These results give evidence for an effective direct bandgap in this material, which is a condition for the high PL. For a different kind of sample, produced by reactive ion etching, a very low wavelength PL peak is observed at 550 nm (2.0 eV). A model of spherical crystalline silicon particles (of up to 706 silicon atoms), saturated at their surface with hydrogen, has been studied by density functional theory. The calculation shows that this nanocrystalline silicon has a direct gap which is substantially larger than the bulk (indirect) gap and is consistent with experimental observation.

We compare the photoluminescence (PL) properties of silicon (Si) single quantum well structures, consisting of an either amorphous or crystalline Si layer of 3 nm thickness, embedded between silicon–nitride layers. These structures are grown by plasma‐enhanced chemical vapor deposition on Si substrates. After crystallization of the originally amorphous Si layers and passivation by hydrogen, strongly polarized PL is observed in the entire visible spectrum. In contrast, a reference structure without the 3 nm silicon layer, but otherwise identical, shows PL in the red and infrared only, but also strongly polarized. Thus, the PL in the blue and green part of the spectrum comes from recombination via Si quantum well states, while the red and infrared PL is due to states at the interface between crystalline Si and silicon–nitride.

Large interfacial voids in bonding and etch-back silicon-on-insulator (BESOI) are discussed. After wafer contacting, the presence of several large interfacial voids is observed. High-resolution X-ray topographs confirm either foreign particles or epitaxial spikes in the center region of voids as the reason for nonbonding. The voids at the bonding interface contain trapped air pockets, which are under pressure. In general, as a result the entire area covered by the voids is lost to the SOI film due to cracking and delamination during the etch-back procedure. In order to investigate the lattice damage distribution and the strain related to it, elastic light scattering experiments were performed. The findings of local networks of elastic distortion are an indication of insufficient wafer flatness and surface finish. BESOI wafers were examined again after they had been subjected to the 30-min high-temperature polymerization bonding step at 1050 degrees C. The areas of the voids that had been free of extended defects following the wafer contracting step then exhibited a dense network of misfit dislocations. During thermal annealing at 1050 degrees C the stresses at the perimeter of the voids and at the site of particulate contamination increased to the point where they exceeded the critical resolved shear stress of silicon and dislocations were nucleated. >

The characterization of semi-insulating InP by means of light scattering (LST) and photoluminescence (PLT) topography and by Raman scattering is discussed. For n-type material wafer uniformity maps of saturation photoluminescence and trap filling time are presented. For InGaAsP layers on InP, the LST map is shown to correlate with device performance. For GaAs, examples in which the maps for near-bandgap (1.49 eV) and for midgap (0.8 eV) photoluminescence are in exact anticorrelation are presented. >

Light emitting Si nanostructures were fabricated by recrystallizing Si/SiNx superlattices grown by plasma enhanced chemical vapor deposition. After recrystallisation by a laser annealing or by rapid thermal annealing the Raman spectra show clearly a confinement effect. A substantial photoluminescence around 470 to 550 nm and at 620 nm is observed after a hydrogen passivation step. The photoluminescence at 620 nm is assigned to carrier recombination via efficient surface states, whereas the blue emission at 470 to 550 nm shows a behaviour expected for quantum confinement effects.

Infrared absorption and Raman scattering measurements of SIMOX structures implanted at various temperatures yield information on the structure and the strain in both the top silicon and the buried oxide layers. Both techniques can also be used to monitor the implant temperature after the implantation.

In this paper we describe experiments aimed at nondestructively evaluating the development of the SIMOX structure with respect to the implanted dose, both before and after annealing. By using nondestructive characterisation techniques we have been able to correlate the observed results with the known microstructure of the specimens. This has enabled us to establish the beginnings of a database, which will enable specimens to be evaluated, for the purposes of quality assurance. We also show the results of light scattering topography which allows the degree of nonuniformity within the implanted region to be qualitatively assessed.

Measurements of light scattering as a function of temperature are reported for single crystalline α-GeTe. A soft mode is observed at 140 cm −2 , assigned as Γ 1 phonon mode, which is responsible for the α-β phase transformation. The eigenvectors of the phonon modes Γ 1 and Γ 3 are determined. The results provide first direct evidence that α-GeTe is a displacive ferroelectric in which the longitudinal optical mode is perfectly screened by the conduction electrons.

The soft mode frequency involved in the structural phase transition in SrTiO3 is measured with high accuracy. Two regimes are observed: a Landau regime remote from Tc and a critical regime near Tc with exponents of 0.5 and 0.33, respectively. This gives evidence for a proportionality of this dynamic quantity with the static order parameter also in the critical regime. The results for the soft mode linewidth are close to the theoretical expectations.

In ferroelectric SbSI the soft mode behaviour is studied by means of Raman scattering. It is observed that coupling occurs between the soft mode and a lower-frequency mode which leads to level repulsion between the two Γ 1 one-phonon states and intensity between the modes.

Visible light emission is observed on laser recrystallised amorphous multi-quantum-well layers. In addition to the 620 nm peak observed in previous work, an intense photoluminescence peak is found in the 470 nm to 550 nm range. While we assign the former to a surface state of high recombination efficiency, the latter shows properties expected for a quantum confinement effect.

The Raman spectrum of flux grown SrTiO 3 shows evidence for a defect mode at 11.5 cm −1 which is held responsible for the brownish color, the conductivity and the unusually low T c .