Interface state density of SiO2/p-type 4H-SiC (0001), (112¯), (11¯00) metal-oxide-semiconductor structures characterized by low-temperature subthreshold slopes

Abstract

Interface properties of heavily Al-doped 4H-SiC (0001) (Si-face), (112¯0) (a-face), and (11¯00) (m-face) metal-oxide-semiconductor (MOS) structures were characterized from the low-temperature gate characteristics of metal-oxide-semiconductor field-effect transistors (MOSFETs). From low-temperature subthreshold slopes, interface state density (Dit) at very shallow energy levels (ET) near the conduction band edge (Ec) was evaluated. We discovered that the Dit near Ec (Ec− 0.01 eV < ET < Ec) increases in MOS structures with higher Al doping density for every crystal face (Si-, a-, and m-face). Linear correlation is observed between the channel mobility and Dit near Ec, and we concluded that the mobility drop observed in heavily doped MOSFETs is mainly caused by the increase of Dit near Ec.