Fermi level depinning and contact resistivity reduction using a reduced titania interlayer in n-silicon metal-insulator-semiconductor ohmic contacts

Experimental evidence of reduction of ultrathin TiO₂ by Ti is presented and its effect on Fermi level depinning and contact resistivity reduction to Si is experimentally studied. A low effective barrier height of 0.15 V was measured with a Ti/10 Å TiO_2-x/n-Si MIS device, indicating 55% reduction compared to a metal/n-Si control contact. Ultra-low contact resistivity of 9.1 × 10^-9 Ω-cm² was obtained using Ti/10 Å TiO_2-x/n+ Si, which is a dramatic 13X reduction from conventional unannealed contacts on heavily doped Si. Transport through the MIS device incorporating the effect of barrier height reduction and insulator conductivity as a function of insulator thickness is comprehensively analyzed and correlated with change in contact resistivity. Low effective barrier height, high substrate doping, and high conductivity interfacial layer are identified as key requirements to obtain low contact resistivity using MIS contacts.