CATHODOLUMINESCENCE DEPENDENCE UPON IRRADIATION TIME

The cathodoluminescence (CL) intensity varies with beam exposure time. In this work, the CL change as a function of irradiation time has bee n studied using various semiconducting materials: CdS single crystal, CdS evaporated thin films, ZnO ceramics and GaAs single crystal. A cur rent density as low as 60 mu m/cm(2) was used in an electron microprob e analyser. In the case of low excitation level, two stages of the CL variation have been generally observed, i.e. increasing and decreasing parts. In the case of a relatively high excitation, only a decreasing stage can be observed. It is believed that the CL time dependence is closely related to the adsorption-desorption process and the surface c ontamination which are stimulated by the electron beam excitation.