Permeable-base transistors with ion-implanted CoSi 2 gate

Abstract

Permeable-base transistors (PBTs) with a buried CoSi 2 gate overgrown by low pressure vapour phase epitaxy have been fabricated by high dose cobalt ion implantation through a gridded mask into n-type Si(111) and Si(100). SiO 2 and SiO 2/W/Cr were tested as implantation mask materials. For the first time different CoSi 2/Si Schottky barrier heights, deduced from I–V and C–V measurements, for the top and the bottom diodes are observed in Si(100) with values of 0.67 ± 0.03 eV and 0.78 ± 0.03 eV respectively. In Si(111) the barrier heights of the top and bottom diodes exhibit a value of 0.78 ± 0.03 eV . The ideality factor of the diodes depends strongly on implantation dose and energy. PBTs on Si(111) obtained by implantation into low doped n-type wafers show a transconductance per gate finger length of 15 mS mm −1, whereas PBTs on Si(100), obtained by implantation into a low doped epitazial silicon layer on a highly doped wafer, exceed 50 mS mm −1 for gate spacings of 1 μm. Pinch-off was achieved in these PBTs.