Laterally Inhomogeneous Schottky Contacts

Abstract

The evaluation of current—voltage curves characterizes each individual Schottky contact by an effective barrier height and an ideality factor. The ideality factors n are generally larger than n _if ,the value determined by the image-force effect only. In other words, the barrier heights depend more strongly on the applied voltage than because of the Schottky effect. Obviously, real metal—semiconductor interfaces are in one way or another not ideal. Ballistic-electron-emission spectroscopy, on the other hand, revealed spatial variations of the local BEEM thresholds or barrier heights on the nm-length scale. The corresponding histograms are well described by Gaussian functions, as verified by the experimental PtSi/n-Si(001) data shown in Fig. 3.16. Hence, regions of reduced barrier height with dimensions smaller than the depletion-layer width embedded in areas of larger but constant barrier height might be a plausible description of real Schottky contacts. Historically, Freeouf et al. [1982a, b] simulated the current transport in such patchy metal—semiconductor interfaces many years before Kaiser and Bell [1988] developed the BEEM technique and Fowell et al. [1990] published the first BEEM studies with lateral nm-resolution.