Enhancement-mode metal/(Al,Ga)As/GaAs buried-interface field-effect transistor (BIFET)

Undoped Al0.5Ga0.5As is used as an insulator layer in the fabrication of MIS-type buried-interface field-effect transistors (BIFETs). The devices had a 2.5 ¿m-long gate and an insulator layer 1000 Å thick. When operated in an accumulation mode the transconductance and maximum current increased from 21 mS/mm and 77 mA/mm at 300 K to 40 mS/mm and 138 mA/mm at 77 K, respectively. The maximum possible 77 K transconductance is calculated as approximately 130 mS/mm. These preliminary experimental results are the best yet reported for a GaAs MIS-type device and represent the first report of enhanced device performance at cryogenic temperatures as a result of an increased electron saturation velocity.