Die Exoelektronen-Emission (Kramer-Effekt) von Zinkoxyd
This work was done, to get new informations about the processes leading to the emission of exoelectrons. The emission-glowcurves of single crystals and of pure and doped powders, after stimulation by X-rays, were measured by means of a G.-M.-counter. Maxima were found at 135° C, 192° C and 260° C. Conductivity-glow-curves of single crystals and films, which were also measured, showed no maximum between 20° C and 280° C. The experiments show that the emission of exo-electrons cannot be a consequence of an enrichement of electrons („Maxwell-tail“) in the conduction band set free from metastable states in the forbidden gap of ZnO during the heating of the specimen. Theoretical considerations lead to the same conclusion. Further it could be shown, that the emission-phenomenon cannot be explained by recombination processes in the depletion layer, if our knowledge of the ZnO band model is correct. It is assumed that the emission-maxima are due to centers in the sorption layer.