Dynamic space charge mechanism in SrS:Ce ac thin-film electroluminescent devices

Dynamic space charge in SrS:Ce ac thin-film electroluminescent (ACTFEL) devices is not a SrS host property. In SrS:Ce ACTFEL devices, a lack of charge injection from interface states leads to space charge formation and to dynamic space charge formation. The dynamic space charge is formed by the impact ionization of Ce and of Ce induced deep level traps. The crystal field symmetry of the Ce3+ site determines its ionization probability. Ce3+ sites of cubic crystal field symmetry have a lower ionization probability than Ce3+ sites with axial crystal field symmetry. A prerequisite for dynamic space charge, i.e., short lived space charge, is the annihilation of space charge. The charge responsible for space charge annihilation originates from trap levels with an activation energy of about 9 meV. The temperature dependence of the annihilation of the space charge is responsible for the observed temperature dependence of the dynamic space charge formation, the conduction charge, and the quantum efficiency. copyright 2001 American Institute of Physics