Electrical resistivity of Ti_n+1AC_n (A = Si, Ge, Sn, n = 1–3) thin films

We have investigated the electrical resistivity of (0001)-oriented Ti_n+1AC_n (A = Si, Ge, Sn, n = 1–3) thin films deposited by magnetron sputtering onto Al₂O₃(0001) substrates at temperatures ranging from 500 to 950 °C. Four-point-probe measurements show that all films are good conductors with resistivity values of ∼21–51 μΩ cm for Ti–Si–C films, ∼15–50 μΩ cm for Ti–Ge–C films, and ∼46 μΩ cm for Ti₂SnC. We find a general trend of decreasing resistivity with decreasing n for the Ti–Si–C and Ti–Ge–C systems due to the increased metallicity obtained with increasing density of A-element layers. We also show that crystalline quality and competitive growth of impurity phases affect the measured resistivity values. The effect of a given impurity phase largely depends on its location in the sample. Specifically, a TiC_x layer in the center of the film constricts the current flow and results in an increased measured resistivity value. However, TiC_x transition or seed layers at the substrate–film interface as well as surface segregation of Ge and Ti₅Ge₃C_x (for Ti–Ge–C) have only little effect on the measured resistivity values. For the Ti–Sn–C system, the resistivity is mainly influenced by the segregation of metallic Sn, yielding a wide spread in the measured values ranging from 20–46 μΩ cm, in the order of increased film purity.