Interpretation for homojunctions of the difference between the theoretical and the experimental built-in potential determined from capacitance measurements, using interface states

The built-in voltage of a junction can be calculated theoretically and determined experimentally from capacitance measurements. The difference that is always found between these two values cannot be completely interpreted by taking into account the contribution to the capacitance of the free carriers. The remaining difference can be explained by assuming the existence of interface states in the vicinity of the junction. Formulas for the depletion-layer capacitance of abrupt and linearly graded junctions with interface states are derived. Experimental data are interpreted in relation to this model.