Application of MBE-grown epitaxial Si/CoSi/sub 2//Si heterostructures for overgrown silicon permeable-base transistors

The fabrication of overgrown silicon permeable-base transistors (PBTs) is described starting from MBE-grown epitaxial Si/CoSi/sub 2//Si heterostructures. Gate fingers are patterned by Ar sputtering followed by low-pressure vapour phase epitaxial overgrowth at 800 degrees C and 0.2 mbar. Results on surface morphology, Schottky-diode characteristics, and PBT performance are presented. It has been recognized that a serious problem of Si PBTs is the field crowding effect at the rim of the thin silicide gate. It cases breakdown at low voltages and limits PBT performance. A diagram indicating the possible operating areas depending on silicide thickness, channel doping, and PBT geometry is presented.