Reflection spectra and luminescence in the exciton region of CdS a t 80 K under the influence of a low energy electron beam (2 to 3 keV) have been investigated. Long-term changes of the spectral lineshape have been observed. It is found that the electron beam produces a negative surface charge, the electric field of which dissociates the excitons in a surface layer. The reflected intensity of light is determined by interference of waves reflected a t the boundaries of the exciton-free layer. The lineshape of the reflection spectra depends on the thickness of this layer.
Es werden Reflexionsspektren und Lumineszenz im Exzitonenbereich von CdS bei80 K unter dem EinfluB eines niederenergetischen Elektronenstrahls (2 bis 3 keV) untersucht. Dabei werden Langzeitanderungen der spektralen Linienform beobachtet. Es wird gefunden, daB der Elektronenstrahl eine negative Oberfllchenladung hervorruft, durch deren elektrischesFeld die Exzitonen ineiner OberflPchenschicht dissoziieren. Die reflektierte Lichtintensitat wird durch Interferenz der an den Grenzen der exzitonenfreien Schicht reflektierten Wellen bestimmt. Die Linienform der Reflexionsspektren hangt von der Dicke dieser Schicht ab.
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