Temperature-dependent Raman scattering of the Ge + GeOx system and its potential as an optical thermometer

Abstract

The phonon behavior of various Ge-based samples has been investigated in great detail. The study comprised Ge films (amorphous and partially crystallized and alloyed with oxygen), crystalline Ge wafers (pristine and alloyed with oxygen), and GeO2 powder. The oxygen-containing samples obtained after thermal annealing the Ge film and Ge wafer correspond to sub-stoichiometric GeO2, or the so-called Ge + GeOx system, in which case [O] ∼40 at.%. A thorough examination of this Ge + GeOx system – as provided by temperature-dependent Raman scattering, their analysis according to the existing theoretical models (involving anharmonic phonon coupling and thermal expansion processes), and a critical review of the literature – indicates the coexistence of practically independent Ge–Ge- and Ge–O-related structures and confirms the presence of both structural and chemical (dis)order. Moreover, the main features regarding the phonon frequencies (ω), line widths (γ), and scattering intensities (IS) of the Ge + GeOx system suggest their suitability in temperature sensing applications. Accordingly, experimentally determined reference curves (i.e., ωT, γT, and IST data described in terms of simple mathematical functions) gave rise to temperature accuracies on the order of 20 K. Everything considered, in its current form, this work presents the first comprehensive analysis-discussion regarding the Ge + GeOx system that, additionally, is being proposed as an effective medium for optical thermometric applications.