Abstract
Interface states in almost the entire SiC band gap are observable by means of x-ray photoelectron spectroscopy (XPS) measurements under bias, although SiC is a wide-gap semiconductor having 2.9 eV band-gap energy. When a layer is formed by wet oxidation at 1000 °C on Si-faced surfaces, only a broad interface state peak is observed at ∼2 eV above the SiC valence-band maximum (VBM), while for dry oxidation at the same temperature, an additional sharp interface state peak is caused at 1.8 eV above the VBM. When the wet-oxidation temperature is increased to 1150 °C, this 1.8-eV interface-state peak also appears. The concentration of graphitic carbon at the interface is found to increase with the heat treatment temperature. The 1.8-eV interface-state peak is tentatively attributed to graphitic carbon with a special structure near the interface. On the other hand, the broad 2-eV interface-state peak is attributed to Si dangling bonds at the interface. Without the 1.8-eV interface-state peak, current-voltage curves measured under x-ray irradiation deviate only slightly from the ideal curve (∼0.4 V), while with this peak, the deviation becomes much larger (∼0.8 V). XPS measurements under bias show that the curves under x-ray irradiation are determined by the magnitude of band bending in SiC. Therefore, the deviation from the ideal curve is attributed to the accumulation of holes (i.e., minority carriers), generated by x-ray irradiation, at interface states with energies between the SiC and metal Fermi levels, causing a downward SiC band-edge shift and thus resulting in a decrease in the magnitude of band bending in SiC. This result demonstrates that the interface states affect characteristics by a static effect (i.e., interface state charges), not by a dynamical effect (i.e., electron-hole recombination at the interface states).
- Received 31 July 2002
DOI:https://doi.org/10.1103/PhysRevB.67.115305
©2003 American Physical Society