Characteristics of a $Zn0.7Mg0.3O∕ZnO$ heterostructure field-effect transistor grown on sapphire substrate by molecular-beam epitaxy

Characterization of a $Zn0.7Mg0.3O∕ZnO$ heterostructure field-effect transistor (HFET) is reported. The HFET was based on a $Zn0.7Mg0.3O∕ZnO∕Zn0.7Mg0.3O$ single quantum well (SQW) grown on an $a$-plane sapphire substrate by molecular-beam epitaxy, and was fabricated by a conventional photolithography technique combined with dry etching. Room-temperature characteristic of the HFET was a $n$-channel depletion type with a transconductance of $0.70mS∕mm$ and a field-effect mobility of $140cm2∕Vs$⁠, in good agreement with the electron Hall mobility in SQW of $130cm2∕Vs$⁠. The on∕off ratio at $VDS=3V$ was $∼800$⁠, which was limited by an insufficiently suppressed leakage current through the bottom $Zn0.7Mg0.3O$ barrier.