COMPUTER-SIMULATION OF ACTUAL AND KELVIN-PROBE-MEASURED POTENTIAL PROFILES - APPLICATION TO AMORPHOUS FILMS

We have employed a first-principles computer program to simulate actual potential profiles and potential profiles obtained experimentally from the Kelvin probe technique. Our results show that the Kelvin probe technique can be used as an in situ method for qualitatively characterizing amorphous films and structures during deposition. However, without additional information about the density and energy distribution of localized states in the bulk and at the free surface, we find that it is difficult to obtain, from the Kelvin probe measurement alone, an accurate quantitative measure of the actual spatial dependence of band bending in films and device structures. In addition, this computer analysis shows that interpretation of the profiles obtained from the Kelvin probe contact potential method can lead to misleading conclusions about the density of states in these amorphous materials. We also show that the barrier height of Schottky contacts or the built-in potential of junctions of differently doped layers can be obtained directly from Kelvin probe contact potential measurements only for films whose free-surface band bending is known from other experimental data. We see that this surface band bending can be significant even for small free-surface-state densities and is more pronounced in higher-quality films.