High spatial and energy resolution characterization of lateral inhomogeneous Schottky barriers by conductive atomic force microscopy

We present a novel approach based on conductive atomic force microscope (c-AFM) for nano-scale mapping in laterally inhomogeneous metal-semiconductors Schottky contacts. For ultra-thin (1-5 nm) metal films with resistivity exceeding by about two orders of magnitude the bulk value, the current localization under the tip (10-20nm diameter) occurs. By spectroscopic analysis of the current-voltage characteristics for different tip positions, the 2D Schottky barrier height (SBH) distribution is obtained with similar to 0.1 eV energy resolution. The method was applied to explain the experimentally observed SBH lowering in macroscopic Au/4H-SiC diodes, in the presence of a not uniform SiO2 layer at the SiC/Au interface. Nano-scale mapping on the oxide free Au/4H-SiC contact demonstrates a SBH distribution peaked at 1.8 eV and with tails from 1.6 eV to 2.1 eV. When similar to 2 mn not uniform SiO2 layer is intentionally grown on SiC before contact formation, the Au/SiO2/4H-SiC SBH distribution exhibits a 0.3 eV lowering in the peak and a broadening (tails from 1.1 eV to 2.1 eV), thus explaining the macroscopically observed average effect.