500°C operation of GaAs based HFET containing low temperature grown GaAs and AlGaAs

A novel FET concept has been developed to overcome the limitations of conventional GaAs based devices operating at high temperature. Due to the replacement of the Schottky gate control diode by a heterojunction, containing AlAs and LTG AlGaAs, and the use of low temperature grown GaAs as buffer layer material, high thermal stability in the electrical performance could be obtained. The device shows DC operation up to 500 degrees C with essentially unchanged characteristics. On wafer microwave measurements were carried out up to 200 degrees C. Whereas f(T) remains essentially unchanged the f(max)/f(T) ratio decreases steadily. Though standard contact metallization was used, destructive degradation occured not before 570 degrees C.