24-mA/mm metal–semiconductor field-effect transistor based on Ge-doped α-Ga2O3 grown by mist chemical vapor deposition

In this study, we developed a metal–semiconductor field-effect transistor (MESFET) using a Ge-doped α-Ga2O3 channel layer grown via mist chemical vapor deposition (CVD). As a buffer layer, Fe-doped α-Ga2O3 was deposited between the Ge-doped α-Ga2O3 channel layer and the m-plane sapphire substrate to reduce the influence of threading dislocations and suppress current leakage. Furthermore, an n+ contact layer heavily doped with Ge was deposited on the channel layer to reduce the contact resistance. The carrier concentration and Hall mobility of the channel layer were 2.1 × 1017 cm−3 and 44 cm2 V−1 s−1, respectively. The transfer length method indicates that the contact between the metal and the n+ layer exhibits Ohmic behavior with a resistance as low as 16 Ω mm. The MESFET exhibited a maximum current of 24 mA/mm and an on-resistance of 587 Ω mm at VGS = 2 V. The Ion/Ioff ratio exceeded 109. The breakdown voltage was 364 V, the leakage current between the drain and the source was below 10−5 mA/mm, and the power figure of merit was 1.2 MW/cm2. These results demonstrate that the mist CVD-derived Ge-doped α-Ga2O3 can give rise to a MESFET with good performance.