Abstract: A source of collimated beam or beams of microwave electromagnetic radiation pulses comprises a photoconductor substrate having a major surface and an optical radiation source providing a beam of optical radiation pulses for illuminating at least a relatively large aperture region of the major surface. A static electric field, intrinsic or applied, is present at the major surface for driving transient photocurrents generated by the beam of optical radiation pulses. Each beam of microwave electromagnetic radiation pulses emitted from the photoconductor substrate may be steered by varying the angle of incidence of the beam of optical radiation pulses illuminating the major surface, by varying the period of the spatial variation of a static electric field applied to the major surface by means of electrodes, or by varying the period or direction of a periodic intensity variation of a spatially modulated beam of optical radiation pulses on the major surface.

Abstract: Direct measurements of electronic device and material response times are made by using high speed photoconductors as both pulse generators and sampling gates.

Abstract: A high speed photodetector using an amorphous semiconductor, such as silicon, and having a localized state density of at least 10.sup.18 /cm.sup.3 is described. The amorphous silicon may be prepared by evaporation or chemical vapor deposition or sputtering.

Abstract: A new mode of optical annealing is disclosed wherein two different wavelength pulses are used to anneal a damaged semiconductor substrate. The first pulse may be of relatively weak intensity, but is strongly absorbed by the solid substrate. The second pulse, which is not strongly absorbed by the solid substrate when in the solid phase, is strongly absorbed by the substrate when in the molten phase. Exposure to the first pulse results in the melting of the substrate, which then becomes highly absorptive to light at the wavelength of the second pulse. Readily available laser sources which are generally not highly absorbed by the semiconductor in the solid phase may thus be efficiently utilized.

Abstract: Polycrystalline and amorphous semiconductors can be annealed using a laser or electron beam to restore or obtain crystal order by epitaxial regrowth on a crystal substrate. When the annealing occurs by liquid phase epitaxy, the presence and lifetime of a molten state at the region being annealed can be used to control the annealing process. Various control mechanisms are described.