The angular correlation of positron-annihilation radiation from single crystals of silicon and germanium has been measured for three different orientations of each crystal. The distributions for the three orientations differ greatly from one another, but each germanium distribution differs from the corresponding silicon distribution only by a scale factor which arises from the difference in the lattice constant. Data are compared with curves calculated using the nearly free-electron approximation for the electron's momentum. It is assumed that the occupied electron states in the crystal fill the Jones zone, a regular dodecahedron bounded by the set of {220} planes in momentum space, and the energy gap is taken to be an adjustable parameter. The fit is extremely good for the radiation emitted in the (110) plane but not so good for the (111) and (100) orientations. Possible reasons for the discrepancies are discussed.

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Vacuum-deposited CdSe thin-film transistors (TFT’s) with reproducible good stability, performance, uniformity, and yield were made using sputtered SiO2 gate insulator, Cr source–drain (s–d) electrodes, and postdeposition annealing in N2. These materials and procedures permit the use of multiple pumpdown fabrication methods with no loss in ac characteristics and little sacrifice in dc stability. Promising results were obtained using photolithography (PL) to delineate s–d electrodes, further simplifying fabrication. The dc instability is electron-trapping type and the drain current decay exhibits a logarithmic time dependence. The slope of this decay curve is used as a parameter to describe device stability and its dependence on the fabrication methods studied: M=0.03–0.06 for one-pumpdown devices, 0.05–0.08 for multiple pumpdown TFT’s, and 0.1–0.2 for TFT’s with PL-delineated s–d electrodes. Preliminary reliability studies show that suitably encapsulated TFT’s have long time stability comparable to the good short time stability observed for fresh devices, indicating the absence of built-in failure mechanisms and the capability for a satisfactory operating life.