Schottky barrier inhomogeneities at contacts to carbon-containing silicon/germanium alloys

In this work, the Schottky barrier height (SBH) of W on n-type and p-type Si1−x−yGexCy pseudomorphic alloys is investigated as a function of the alloy composition. The epilayers were grown either by RTCVD or MBE. Electrical characterizations of contacts were achieved through current–voltage measurements in the temperature range 150–300 K. As soon as the amount of C exceeds 1.1%, the ideality factor n increases up to high values, such as 1.7 for y=1.8%. In addition, the SBHs (Φb) decrease with lowering temperature, while the ideality factors (n) become larger. A linear dependence Φb (n) is observed for all the samples. Similar trends have already been reported for contacts on other semiconductors and have been explained by assuming lateral inhomogeneities at the interface. The SBHs of laterally homogeneous contacts can be obtained by extrapolation of experimental Φb (n) plots to n=1. The results show homogeneous interfaces for the Si1−xGex binary alloys and inhomogeneous interfaces for the carbon-containing alloys. The inhomogeneities of the interface are discussed in terms of local strain or (and) defects due to the C-incorporation.