Nearly Fermi-level-pinning-free interface in metal/heavily-doped SiC Schottky structures

The barrier heights in Ti/ and Ni/n-SiC Schottky barrier diodes (SBDs) in a wide range of the donor density (Nd = 2 × 1017-1 × 1019 cm−3) were investigated. The forward current-voltage characteristics in the heavily-doped SBDs (Nd > 2 × 1017 cm−3) are described by the thermionic field emission (TFE) model, which includes an electron tunneling induced by the high electric field (> MV cm−1) at the Schottky interface. The high electric field also causes significant image force lowering (Δφ ∼ 0.2 eV) in the heavily-doped SBDs (Nd = 1 × 1019 cm−3). Through the analysis carefully considering such strong image force lowering, the same slope of the barrier height versus the metal work function plot (S ∼ 0.7) is obtained regardless of Nd. This indicates that metal/SiC interfaces are nearly free from Fermi-level pinning independent of Nd.