Ultraviolet emission from YAlO3:Gd3+ thin film electroluminescent devices fabricated on perovskite-type oxide substrates

Abstract

Inorganic ultraviolet-electroluminescent (UV-EL) devices with a Gd3+-doped YAlO3 thin film emitting layer were fabricated by radio frequency sputtering. Three kinds of perovskite-type oxide substrates, namely a SrTiO3 single crystal (STO-SC), BaTiO3 single crystal (BTO-SC), and BaTiO3 polycrystalline disk (BTO-PC), were used for the devices. The influence of the substrates on the UV-EL properties of YAlO3:Gd3+ was investigated. It was found that EL threshold voltage, emitting locations, and EL intensity have changed depending on the substrates. The UV-EL attributed to the 6PJ-8S7/2 transitions in Gd3+ was observed in the BTO-PC substrate device with applied voltage of approximately over 200 V and in the STO-SC and BTO-SC substrate devices with that of approximately over 500 V. The STO-SC and BTO-SC devices showed EL only near the edges of a back electrode, whereas the BTO-PC device showed surface EL over the whole electrode. It was considered the local EL at the electrode edges in the SC substrate devices was caused by a concentrated electric field in the vicinity of the electrodes. The BTO-PC device showed not only the lowest EL threshold voltage but also the most intense EL in the three devices. Because the BTO-PC substrate has a high dielectric constant and appropriate surface roughness, which results in a high and uniform electric field over the back electrode, the YAlO3:Gd3+ emitting layer showed intense surface UV-EL with lower applied voltage.