Nanometer-Scale Investigation of Schottky Contacts and Conduction Band Structure on 4H-, 6H-, and 15R-SiC using Ballistic Electron Emission Microscopy

Abstract: We have performed ballistic-electron emission microscopy (BEEM) of Pd and Pt Schottky contacts on 6H- and 4H-SiC and Pd Schottky contacts on 15R-SiC. Measured Schottky barrier heights (SBH’s) appear spatially uniform up to the fitting error due to noise (~0.03 and ~0.1 eV for 6H- and 4H-SiC, respectively). In 4H-SiC, we observed an additional conduction band minimum (CBM) ~0.14 eV above the lowest CBM, which is in good agreement with our band theoretical calculation. Preliminary results on Pd/15R-SiC indicate a higher CBM ~0.5 eV above the lowest CBM, and possibly another higher CBM ~0.3 eV above the lowest CBM. Also, in Pd/15R-SiC, large variations in BEEM spectra at different locations were observed, suggesting an inhomogeneous interface. Additionally, we sometimes observed enhancement in ballistic transmittance over regions intentionally stressed by hot electron injection. We report ballistic-electron emission microscopy (BEEM) measurements of Pd and Pt Schottky contacts on 6H- and 4H-SiC, and Pd contacts on 15R-SiC. The BEEM technique is an extension of scanning tunneling microscopy (STM) and can be used to probe local electronic properties of buried metal/semiconductor interfaces with nanometer-scale spatial resolution and high energy resolution [1,2]. Figure 1 shows the schematic experimental setup with corresponding energy-level diagram