Thermal expansion coefficients and unit cell parameters for r-GeO2 heteroepitaxy on r-TiO2/Ti1− <i>x</i> Ge <i>x</i> O2

Abstract

The disclosure of the full potential of rutile germanium dioxide (r-GeO2) as a new generation material for power electronics requires the development of its heteroepitaxy. In this context, the isostructural r-TiO2 is one of the most investigated substrates, often requiring buffer layers to accommodate lattice mismatch. In this work, we investigate, via in situ variable temperature powder x-ray diffraction, the thermal expansion behavior of r-TiO2, r-GeO2, and the limit solid solution r-Ti0.88Ge0.12O2. The collected data allowed an extraction, under identical experimental conditions, of lattice parameters and thermal expansion coefficients. Based on these results, in-plane lattice mismatch was evaluated as a function of temperature, considering all the commercially available r-TiO2 single crystal cuts [i.e., (001), (110), (111), (100), and (101)] and extrapolating data up to reasonable r-GeO2 deposition temperatures. The r-Ti1−xGexO2 solid solution is shown to effectively reduce both the mismatch and its thermal evolution, highlighting its potential as an effective strain-engineering buffer layer. These findings depict a comprehensive framework for the optimization of r-GeO2 heteroepitaxy.