On the inappropriate use of the intrinsic level as a measure of the electrostatic potential in semiconductor devices

The relationship between the intrinsic Fermi level Eiand the electrostatic potential φ is reviewed in detail. It is shown that, contrary to popular belief, Eihas no physical significance and cannot be used in general as a reference for φ. The local vacuum level gives the spatial variation of φ and is defined in the context of the energy-band diagram. These results pertain directly to the analysis of devices with nonuniform band structure, such as heterojunctions.