Effects of surface/interface states on Schottky contacts for 4H-SiC

Electrical characteristics of sputter deposited Ni, Cr, Au, Pt, and Ti contacts on 4H-SiC were studied. The 4H-SiC substrates used were test grade, single crystalline, and n-type. These contacts were found to be rectifying. Saturation current densities, ideality factors and Schottky barrier heights were determined from these measurements. Argon plasma sputtering degraded the contact by increasing the reverse current and lowering the turn-on voltage. The calculated Schottky barrier heights were ranged from ∼ 0.8 eV to ∼ 13 eV and reverse current was found to be as low as 136.5 nA/cm² at -5 V. For RCA cleaned samples, the barrier heights are weakly dependent on metal work function and were largely determined by metal induced gap states (MIGS) and electronegativity difference between metal and semiconductor. However, in RCA + Ar plasma sputter cleaned samples, the barrier heights were independent of the metal work function determined entirely by MIGS and surface/interface states.