Depth profiles of the Fermi level at an amorphous-carbon nitride/SiO₂/n-type-Si heterojunction interface obtained by Kelvin probe force microscopy

To explore the work function of a typical amorphous-CN film containing a nitrogen concentration of 23.5 at.%, surface potential images were acquired using Kelvin probe force microscopy. Based on the Fermi level of the n-type Si and the contact potential difference between the amorphous-CN film and the n-Si substrate, the work function of the amorphous-CN film was estimated to be 5.2 ± 0.2 eV below its vacuum level. Using the surface potential depth profile for an etched amorphous-CN film, energy diagrams of the amorphous-CN/SiO₂/n-Si interface were constructed based on the positional relationship of the Fermi level. These band diagrams showed that band bending occurred at the amorphous-CN/SiO₂/n-Si interface despite the Fermi level pinning effect of surface trapping due to the SiO₂ insulator layer.