Complex-refractive-index profiles of 4 MeV Ge ion-irradiation damage in silicon

Abstract A new optical method is introduced for the determination of optical depth profiles in silicon. Alterations of the refractive index n and of the extinction coefficient k can be resolved down to 5 × 10−4 with a depth resolution of 20 nm. The case of 4 MeV Ge ion-irradiation damage has been chosen to demonstrate the way how n and k are evaluated from reflection and transmission profiles measured at the bevelled surface of silicon samples. Wedge interference fringes in the reflection profile are used to determine the photon energy dependent optical constants of ion-irradiated amorphous silicon between 1.1 and 2.5 eV. The different dose dependence (2 × 1012–1 × 1016 Ge ions cm−2) of the n and k profiles at a photon energy of 1.28 eV is interpreted by the irradiation induced generation of different types of defects such as amorphous clusters and defectively coordinated silicon bonds.

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