PHOTOCONDUCTOR-SEMICONDUCTOR EMITTERS.

New laboratory facilities recently completed and now in full operation, are described. These facilities represent an improvement over the old ones, particularly with regard to cleanliness and convenience for photoemission research. Several improvements in the experimental arrangements enable greater accuracy to be obtained, and other improvements result in increased speed and reduced man-effort in reducing the raw spectrometer data to final spectral plots. Measurements were made of photoelectric work function as a function of BaO film thickness these measurements corroborate previously reported data. It has been demonstrated that continued evaporation of BaO onto a heated substrate results in a reduction in the photoelectric work function below that obtained for an optimum film thickness of 10 to 15 monolayers. The emission near threshold is believed to be photoemission from levels in the BaO itself at higher h Nu values above about 1.35 eV, the emission is believed to originate in the metal substrate. It was demonstrated that moderately high external fields reduce the photoelectric work function and increase the quantum efficiency. A similar effect has been observed by shining white light onto the photocathode. The enhancement of photoemission owing to electron bombardment of the BaO was observed again for thin BaO films however, the effect was not observed for thick films. The enhanced photoemission of a heated photocathode reported previously was noted again this time with thick BaO films, and this effect was studied intensively.