Two Dimensional Imaging of the Laterally Inhomogeneous Au/4H-SiC Schottky Barrier by Conductive Atomic Force Microscopy

We present a novel approach based on conductive atomic force microscopy (c-AFM) for nano-scale mapping of the Schottky barrier height (SBR) between a semiconductor and an ultrathin (1-5 nm) metal film. The method was applied to characterize the uniformity of the Au/4H-SiC Schottky contact, which is attractive for applications due to the high reported (similar to 1.8 eV) SBH value. Since this system is very sensitive to the SiC surface preparation, we investigated the effect on the nano-scale SBH distribution of a similar to 2 run thick not uniform SiO2 layer. The macroscopic IN characteristics on Au/SiC and Au/not uniform SiO2/SiC diodes showed that the interfacial oxide lowers the average SBH. The c-AFM investigation is carried out collecting arrays of IN curves for different tip positions on 1 mu mx1 mu m area. From these curves, 2D SBH maps are obtained with 1020 nm spatial resolution and energy resolution < 0.1 eV. The laterally inhomogeneous character of the Au/SiC contact is demonstrated. In fact, a SBH distribution peaked at 1.8 eV and with tails from 1.6 eV to 2.1 eV is obtained. Moreover, in the presence of the not uniform oxide at the interface, the SBH distribution exhibits a 0.3 eV peak lowering and a broadening (tails from 1.1 eV to 2.1 eV).