SPACE-CHARGE AND EXCITATION EFFICIENCY IN ZNS THIN-FILM ELECTROLUMINESCENT DEVICES

Measurements under continuous UV illumination permit one to investigate the influence of a bulk space charge on the excitation efficiency eta(exc) in ZnS thin film electroluminescent devices. Depending on the irradiation intensity, the addition of UV reduces or even erases the space charge which is responsible for the inhomogeneous excitation efficiency. When the space charge is reduced, eta(exc) is higher in the region near the anodic insulator-semiconductor interface. In another experiment, neodymium doped ZnS samples are used to determine the variation of the space charge during the charge transfer. Under our driving conditions, the space charge increases during the charge transport in the steady state regime.