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Roughness effects in the infrared reflectance of thick 3C-SiC films grown on Si substrates

We have analyzed the IR reflectivity spectra of micrometric SiC deposited on Si substrates by the CVD technique under different growth conditions. We show that the roughness at the SiC/Si interface gives rise to a damping of the interference fringes above the reststrahlen band without introducing any change of the mean value of the optical response which shows to be dispersionless. On the opposite, roughness at the SiC surface manifests through a falling of the reflectivity on the LO side of the reststrahlen band with respect to the TO one side, and a damping of the interference fringes together with a progressive decrease of the reflectance with increasing IR frequencies. These effects give account for most of the deviations from the optical response associated to the specular reflectance of flat surfaces in SiC/Si heterostructures with a low level of free carriers concentration.