Effect of ZnO buffer layer on the cathodoluminescence of ZnGa2O4/ZnO phosphor screen for FED

A ZnGa2O4/ZnO phosphor screen for FED was prepared by RF magnetron sputtering. The ZnO buffer layer has a reasonable resistivity of about 5.2×103 Ω cm and a high transparency larger than 85%. The ZnGa2O4 phosphor was polycrystalline on ITO, yet it was amorphous on ZnO. If the ZnGa2O4/ZnO phosphor screen was annealed at temperatures above 300 °C, then ZnGa2O4 was crystallized. Owing to the lattice mismatch between ZnGa2O4 and ZnO, the grain size of ZnGa2O4 on ZnO was small. As a result, the effective emission area and luminescence of the ZnGa2O4/ZnO phosphor screen were enhanced. Auger electron spectroscopy (AES) examination showed that atoms in ZnO did not diffuse into ZnGa2O4 film, and the ZnGa2O4 was Zn-deficient. For charge balance, oxygen vacancy defects in the phosphor film were formed to compensate Zn deficiencies; consequently, the probability for electrons transfer from 2EB to 4A2 of Ga energy levels was improved and the luminescence of the phosphor was increased.