Effect of Schottky gate type and channel defects on the stability of transparent ZnO MESFETs

Transparent metal–semiconductor field-effect transistors (MESFETs) were fabricated on ZnO thin films deposited using a filtered cathodic vacuum arc. MESFETs with silver oxide (AgOx) and iridium oxide (IrOx) Schottky gates with mobilities up to 70 cm2 V−1 s−1 were subjected to extensive bias and illumination stress tests. Device instability appeared to be strongly dependent on gate metal type, bias conditions and ZnO film morphology. Positive bias stress of AgOx gated devices resulted in irreversible damage that is thought to be due to Ag electromigration across the gate interface. IrOx gated devices showed superior stability with only a small recoverable decay in channel current that was associated with the charging of grain boundary defects.