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It is well known that recombination lifetimes are significantly degraded in oxygen-precipitated silicon. The possible sources for lifetime degradation are expected to be oxygen precipitates (OP’s), dislocation loops, stacking faults, and point defects associated with self-interstitials generated during the oxygen precipitation process. From the results of an extensive experimental study using IR absorption, TEM, DLTS, and SPV (surface photovoltage), we have found that OP’s are mainly responsible for the observed lifetime degradation and that recombination at OP’s takes place through Si/OP interface states. In addition we have observed that the lifetime degradation is more severe in p-Si than in n-Si even for identical densities and sizes of OP’s. A model for recombination at OP’s is presented in terms of the surface recombination velocity at the Si/OP interface and their average density and size. To explain the lifetime difference between n-Si and p-Si we propose a band bending around OP’s caused by positive fixed charges in the OP’s.

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Absfracf-The recently developed large-area field-emission photocathode is described. It consists of a finely spaced array of point emitters fabricated by etching of p-type silicon or other semiconductor. Uniform emission over areas of 6-7 cm2 have been obtained. For Si, the spectral response extends from 0.4 to 1.1 pm. Quantum yields of 25 percent at 0.86 pm have been measured, which is about five times the value reported for the extended S-20 photocathode and comparable to the best 111-V photoemitters. Calculations indicate that quantum yields of up to 40 percent at 0.86 rm and 28 percent at 0.9 pm are attainable with the present photocathode structures. For low dark current densities, photocathode cooling to temperatures approaching 77 IC must be employed at present. The dark current is shown to be dominated by surface-generated electrons in the space-charge region of the emitters. Effects of phosphorus gettering and annealing treatments on dark current are discussed, and the spatial frequency response of the device is determined. The results of a computer study show that the field intensification factor of p-semiconductor field emitters behaves quite differently from that of metallic emitters.