NEC (United Kingdom)

Crossed-grid dislocations in (001)-oriented silicon wafers, which are associated with bright spots in silicon vidicon images, are investigated by means of X-ray topography. They are found to have only Burgers vectors inclined to the wafer surface and to lie at a depth of more than 30 µm with a fairly uniform dislocation density. It is speculated that they originate from some stress-concentrated points at the oxidizing surfaces and grow by glide and cross slip to relieve elastic strain caused by the attachment of an oxide film.

A new model of the generation of the dislocation network associated with dark-line-defects (DLDs) in rapidly degrading double-heterostructure laser crystals is proposed. The degradation can also be explained by this model, i.e., it may be associated essentially with the first stage of the development of the dislocation network which is based on the conservative propagation of screw dislocation segment and, thus, does not require point defect sources. The second stage of the development may be the widening and twisting of the trace of the dipole dislocation by a combination of climb and glide. The image of DLDs would thicken after the second stage of the development. The observed characters of DLDs such as directionality, existence of loops, and so on, can be well explained in the light of the new model.

For oriented MnBi films, the diagonal and off-diagonal components of the complex dielectric tensor were determined from optical and magneto-optical data measured in the 425 to 1000 nm wavelength range. The complex dielectric tensor indicates that several electronic transitions contributed from the magnetic electrons are located in the 600 to 1000 nm wavelength range, and may be responsible for the large Faraday rotation of MnBi films over this wide wavelength range. The Kerr rotations for s and p polarized waves were measured and calculated from the dielectric tensor as a function of the incident angle at 632.8 nm. The calculated results can explain the general behaviour of the dependence of the measured Kerr rotations on the incident angle.

Physical, chemical and electrical properties of Si rich silicon nitride (SiN) film deposited by using the SiH4–NH3 system have been studied. By changing the volume ratio of NH3 to SiH4 from 100 to 1/30, samples with varying excess Si content within SiN films can be obtained. The current conduction mechanism of the SiN film can be represented by the superposition of Poole-Frenkel current, field ionization current and hopping current as reported by Sze in the Si3N4 films without Si excess. Energy levels of trapping centers responsible for Poole-Frenkel current become shallow while their densities remain nearly constant as a function of the Si content. From the dependence of the shift characteristics of C–V curves, it has been deduced that the maximum charge storage within the SiN film is controlled by current conduction through the film.

C–V and I–V characteristics of MAS and MAOS diodes are measured directing special care to voltage region of deep inversion. Two types of characteristics are observed depending upon carrier types of semiconductor substrate. A simple mathematical model of two carrier charge transport and storage is developed and clarified the underlying mechanisms for these types of characteristics. It is concluded that, under positive bias voltages, injection of electrons from Si conduction band into Al2O3 film takes place while, under negative bias voltages, injection of electrons from Al2O3 into Si conduction band occurs. A region of steeply rising current in I–V curves and its correlation with shift characteristics of VFB are found and interpreted in terms of space charges associated with traps.

The Fresnel zone plate is extended, and its application to synthesize optical images is presented.First, the fixed-width zone plate is introduced. It is a modification of the Fresnel zone plate conventionally used, and has a simple shape easy to produce. The effect of modification is discussed. Then a method to produce the extended zone plate which can focus not only an image of point but also an image of curve is presented. The extended zone plate of fixed width is used in the form of off-axis. This zone plate gives an image with good contrast, and the time to produce the zone plate is saved very much. The required image is obtained as the sum of partial images which are gotten by using the extended zone plate. Several examples of the images synthesized by this method are shown.Moreover, the 3 D-extended zone plate and the color extended zone plate are proposed to synthesize a continuous three-dimensional image and a color image, respectively.The zone plate has been drawn by the computer controlled drafter on a paper, and then photoreduced for production.