TRANSIENT MEASUREMENTS OF THE EXCITATION EFFICIENCY IN ZNS-BASED THIN-FILM ELECTROLUMINESCENT DEVICES

A series of electric pulses is applied to virgin alternating-current t hin film electroluminescent ZnS-based samples in order to investigate the behaviour of the excitation efficiency within the first drive peri ods. One observes a decrease of the excitation efficiency from the fir st pulse on. The steady state values of the transferred charge and the excitation efficiency are attained after about ten drive periods. The se transient measurements permit one to investigate the establishment of the bulk space charge in the ZnS layer in this kind of devices.