Here, we describe the fabrication of diffraction gratings in the {100} surfaces of silicon by preferential etching. The gratings thus made have grooves with well-defined geometric shape and bounded by nearly perfect reflecting walls. Meanwhile, the importance of utilizing this technique in integrated optics is also discussed.

Outstanding lasing characteristics of a new GaAs-(GaAl)As ring laser is reported. The basic structure of the new laser includes a circular resonator and straight output branching waveguide. The possibility to eliminate the need for feedback reflectors should make it attractive for integrated optics applications.

A simultaneous exposure and development technique for forming diffraction gratings and recording holograms in positive photoresist is described. This technique not only reduces the exposure time significantly, but is also able to produce gratings with deep grooves and sharp ridges. With the photoresist placed in a liquid-filled prismlike container, the smallest period obtainable by this method is reduced by a factor equal to the index of refraction of the liquid.

Measurements of surface conductance, photoconductance, dark field effect, and field effect under illumination were made on single crystals of w-type and ^>-type germanium. The samples, freshly etched with CP-4, were exposed to the Brattain-Bardeen ambient cycles. During early cycles, the measurements were irreproducible. The irreproducibility was due to changes in the density of the dominant surface recombination centers. The density of these centers varied by an order of magnitude during the ambient cycle, whereas the energy levels and the capture probabilities remained constant. With these assumptions, quantitative agreement between theory and experiment was obtained. From the changes in the photoconductance and the dark-field effect during repeated ambient cycles, the density of the dominant recombination centers was found to change at the same rate as the density of the "fast" states near the center of the gap. In addition, the recombination centers and the "fast" states have the same energy levels. Therefore, the recombination centers and "fast" states are identical.

A bevel has been etched in a GaAs epitaxial film grown on Si substrate, so that Raman spectrum of GaAs layers can be measured as a function of distance from the GaAs/Si interface. The amount