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Optical constants of germanium and thermally grown germanium dioxide from 0.5 to 6.6eV via a multisample ellipsometry investigation

2016; Volume: 34; Issue: 6 Linguagem: Inglês

10.1116/1.4963075

2166-2754

T. Nathan Nunley, Nalin Fernando, Nuwanjula S. Samarasingha, Jaime M. Moya, C. M. Nelson, Amber A. Medina, Stefan Zollner,

Thin-Film Transistor Technologies

Thermal GeO2 oxides up to 136 nm thickness were produced by annealing Ge wafers in pure oxygen at 550 °C and 270 kPa pressure for up to 10 h. The oxidation kinetics followed the Deal–Grove law. Using multisample spectroscopic ellipsometry for a series of five thermal oxides with different thicknesses, the complex dielectric functions of Ge and GeO2 were determined from 0.5 to 6.6 eV, for thin-film metrology applications in Ge-based microelectronics and photonics. The dispersion of the GeO2 layer was modeled with a simple Tauc-Lorentz oscillator model, but a more complicated dispersion with eight parametric oscillators was required for Ge. A reasonable fit to the ellipsometric angles could be obtained by assuming that all thermal oxides can be described by the same dielectric function, regardless of thickness, but a slight improvement was achieved by allowing for a lower density oxide near the surface of the thickest films. The authors compare their results with literature data for Ge and bulk and thin-film GeO2.