Electric and Electroluminescent Properties of the Surface Layers of ZnS : Mn, Cu, Cl Films

概要

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Current (I)-voltage (V) and capacitance (C)-voltage (V) characteristics of the vacuum-evaporated films of ZnS : Mn, Cu, Cl were measured. I-V curves were similar to the diode characteristics. And its cut-off voltage was about 1.1 volts. C^<-2>∞V relations also gave a diffusion potential 1.1 volts. However, it seems that these characteristics are not due to the metal-ZnS contact but to the surface structure of films (Cu_<2-x>S-ZnS junction), since differences in cut-off voltage or diffusion potential were not observed either in Au or in Cu electrodes. The band gap of the excessive Cu layer was estimated at about 1.27 eV. That is to say, an excessive Cu is thought to exist as Cu_<2-x>S on the surface of ZnS : Mn. Cu, Cl films, and p-Cu_<2-x>S-n-ZnS heterojunctions are formed at the surface layer of ZnS : Mn, Cu, Cl films. At the forward-biased junctions, holes are injected into n-ZnS phase from p-Cu_<2-x>S phase, and consequently EL emission with 580 mμ peak can be observed by Mn^<2+> which involves the energy transfer from Cu^+ centers to Mn^<2+> centers. EL emission localized at the anode in gap cells and EL emission in the forward-biased sandwich cells can be explained by the model of heterojunction mentioned above. On the other hand, EL emission localized at the cathode in gap cells and EL emission in the reversebiased sandwich cells under the high voltage are thought to be due to the usual mechanism of impact excitation.
東北大学の論文