Lattice misfit versus performance of thin film electroluminescent structures

Thin polycrystalline electroluminescent thin films (TFEL) of ZnS:Mn (phosphor) and $Y2O3$ (insulator) were deposited individually or as multilayers onto Si (100) substrates. Their crystallinity and the luminescent efficiency of the phosphor films were investigated at varying thermal annealing temperatures. It is shown that the luminescent quality of the phosphor layer increases up to $700 °C,$ whereas the electroluminescence operating intensity of TFEL devices saturates at $500 °C.$ The structural analysis of the insulating and phosphor layers shows that they recrystallize at annealing temperatures of, respectively, 500 and $600 °C,$ and that their lattice misfit doubles at processing $temperatures>=500 °C.$ Since TFEL devices should benefit from enhanced luminescence efficiency and crystallinity at high annealing temperatures, we suggest that the lack of improvement in device performance beyond $500 °C$ is due to interface alterations. According to previous works, we propose that the lattice misfit increase between the phosphor and dielectric thin films modifies the morphology of the phosphor–insulator boundary inducing a modification of the interface states density, and hence, modifying high field electron transport properties of TFEL devices.