Schottky Barrier Lowering Induced by Ultrathin Aluminum Oxynitride interlayer in Metal/SiC Junctions

Abstract

Silicon Carbide (SiC) has been considered as the most promising wide band gap semiconductor for developing high power electronic devices. The electrical characteristics of SiC Schottky diode depend strongly on the interface energy barrier (Schottky barrier) and a lower Schottky barrier is advantageous to improve the power efficiency and acquire the fast switching. We report experimentally that the Schottky barrier of metal/SiC junction is reduced significantly with an ultra-thin (down to ~1.0 nm) aluminum oxynitride (AlON) interlayer inserted at the junction interface. The AlON thin film was deposited by using the RF magnetron sputtering with the in-situ flashing for removing the native oxide on the SiC surface and the grown AlON thin film was confirmed to be amorphous from high-resolution transmission electron microscope (HR-TEM) images. The Schottky barriers of metal/AlON/SiC and metal/SiC junctions were obtained by performing current-voltage (I-V), capacitance-voltage (C-V), and internal photoemission (IPE) measurements. It was also found that the contact resistance of junction decreased with the AlON interlayer. The Schottky barrier was reduced by up to ~0.8 eV and the reduction was similar for three types of metal with different work function (Pt: 5.65 eV, Ni: 5.01 eV, Cu: 4.33 eV). The adjustment of Schottky barrier with an interlayer is normally considered to be due to the potential change driven by fixed changes in the interlayer or Fermi-level depinning associated with the supression of metal-induced gap states. In our case, the Fermi-level pinning factor remained almost unchanged, implying that the surface states of SiC is NOT the main factor of the observed Schottky barrier reduction. It seems most likely that the Schottky barrier reduction arises from the fixed positive charges in the AlON thin film.