Interface properties of 4H-SiC (1120) and (1100) metal-oxide-semiconductor (MOS) structures annealed in nitric oxide are characterized by conductance, high-low, and C-ψ s methods. Compared with 4H-SiC (0001) MOS structures, generation of very fast interface states by nitridation is much smaller in 4H-SiC (1120) and (1100). The effective mobility of planar MOSFETs fabricated on Al + -implanted p-body doped to 1×10 17 cm −3 is 103 cm 2 /Vs on (1100), 92 cm 2 /Vs on (1120), and 20 cm 2 /Vs on (0001). The mobility-limiting factors are discussed on the basis of experimental results. The high channel mobilities for (1120) and (1100) MOSFETs can be correlated with the lower density of fast interface states generated by nitridation.Index Terms-Channel mobility, fast interface states, interface state density, nonpolar face, silicon carbide.

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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.

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