Enhanced thermal stability of Ti/TiO_2-Ge contacts through plasma nitridation of TiO_2 interfacial layer

摘要

This work demonstrates a solution to the problem of increase in Schottky barrier height (ф_B) with thermal annealing (thermal instability) in unpinned (low ф_B) Ti/TiO_2-Ge metal-interfacial layer (IL)-semiconductor (MIS) contacts through plasma nitridation of the TiO_2 layer. Unlike TiO_2, unpinned (ф_B =0.09eV) TiO_xN_y contacts are thermally stable for anneals up to 30 min at 400 °C. The thermal stability improves with increasing nitrogen concentration ([N], 2.5-9.5%) and is independent of thickness (2-5 nm) for [N] = 9.5%. Additionally, the plasma nitridation process is shown to increase the oxygen vacancy concentration (n-type doping) and reduce the ф_B dependence on TiO_xN_y thickness in unannealed TiO_xN_y contacts. Enhanced thermal stability is attributed to the incorporated nitrogen acting as a diffusion barrier that prevents contact pinning through reduction of the TiO_2 layer by contact metal during the anneal, as well as preserves the amorphous nature of the IL along with its fixed charge and interfacial dipoles that contribute to ф_B reduction.