C–V characterization of Schottky- and MIS-gate SiGe/Si HEMT structures

Abstract Electrical properties of Schottky- and metal–insulator–semiconductor (MIS)-gate SiGe/Si high electron mobility transistors (HEMTs) were investigated with capacitance–voltage ( C–V ) measurements. The MIS-gate HEMT structure was fabricated using a SiN gate insulator formed by catalytic chemical vapor deposition (Cat-CVD). The Cat-CVD SiN thin film (5 nm) was found to be an effective gate insulator with good gate controllability and dielectric properties. We previously investigated device characteristics of sub-100-nm-gate-length Schottky- and MIS-gate HEMTs, and reported that the MIS-gate device had larger maximum drain current density and transconductance ( g m ) than the Schottky-gate device. The radio frequency (RF) measurement of the MIS-gate device, however, showed a relatively lower current gain cutoff frequency f T compared with that of the Schottky-gate device. In this study, C–V characterization of the MIS-gate HEMT structure demonstrated that two electron transport channels existed, one at the SiGe/Si buried channel and the other at the SiN/Si surface channel.