The effect of mound roughness on the electrical capacitance of a thin insulating film

We investigate the influence of the roughness at a nanometre scale on the e lectrical capacitance of thin films. It is shown that the surface roughness causes an increase of the electrical capacitance depending on the details of the roughness characteristics. For mound rough surfaces, the increase of the electrical capacitance depends strongly on the relative magnitude of t he average mound separation lambda and the system correlation length zeta. A rather complex behaviour develops for zeta > lambda, whereas for zeta < < lambda> a smooth decrease of the capacitance as a function of the average m ound separation A occurs due to surface smoothing. Depending on the film th ickness, the presence of roughness strongly influences the electrical capac itance as long as zeta < lambda, whereas a precise determination of the act ual effect requires a detailed knowledge of the thickness dependence of the roughness parameters during him growth. (C) 2001 Elsevier Science Ltd. All rights reserved.