Interface state density of SiO_2/p-type 4H-SiC (0001), (1120), (1100) metal-oxide-semiconductor structures characterized by low-temperature subthreshold slopes

摘要

Interface properties of heavily Al-doped 4H-SiC (0001) (Si-face), (1120) (a-face), and (1100) (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 (D_(it)) at very shallow energy levels (E_T) near the conduction band edge (E_c) was evaluated. We discovered that the D_(it) near E_c (E_c - 0.01 eV ＜E_T＜ E_c) 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 D_(it) near E_c, and we concluded that the mobility drop observed in heavily doped MOSFETs is mainly caused by the increase of D_(it) near E_c.