Optical properties of SiO2/Si layers enriched in germanium by ion implantation

Abstract

Germanium ions have been doubly-implanted with different energies and fluences to obtain a quasi-rectangular depth distribution of Ge atoms in a 700 nm thick SiO? layer on Si. Subsequently, the samples were annealed at temperatures in the range from 700°C to 1100°C for 1h. The depth distribution of Ge atoms in these layers were determined from the Rutherford backscattering (RBS) measurements. For the samples annealed at temperatures higher than 800°C the diffusion process of Ge atoms takes place in two directions: towards the implanted surface and to the Si02/Si interface. The refraction index n and extinction coefficient к are materials parameters important from the point of view of optoelectronic applications. Their values were obtained with a help of the Multiple Angles of Incidence Ellipsometry (MAIE) investigations. It was observed that the value of refraction index of the Si02/Si layer increases about 2% after implantation in a comparison with the unimplanted SiOs material. Subsequent annealing reduces the refractive index, but the pre-implantation value is not attained, is noticed with the increase of the annealing temperature. This effect can be explained by defect dependent volume change in implanted layer and the change of atomic bond polarizability.