Vibrational and optical identification of GeO₂ and GeO single layers: a first-principles study

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Germanium oxides (GeO₂ and GeO) are crucial materials with potential applications in electronics and optoelectronics.
• Understanding their distinct structural phases and properties is essential for targeted material design.

Purpose of the Study:

• To computationally identify and characterize two hexagonal phases of germanium oxides: germanium dioxide (GeO₂) and germanium monoxide (GeO).
• To investigate their dynamical stability, vibrational properties, electronic band structures, and optical characteristics.

Main Methods:

• Density Functional Theory (DFT) for structural optimization and phonon band dispersion calculations.
• G₀W₀-Bethe Salpeter Equation (BSE) calculations for optical properties, including absorption, reflectance, and transmittance spectra.
• Prediction of off-resonant Raman spectra for phase identification.

Main Results:

• Single-layer GeO₂ and GeO were found to crystallize in stable 1T and buckled phases, respectively.
• Characteristic Raman spectra were predicted for each phase, enabling identification.
• Electronic band structure analysis revealed insulating GeO₂ and semiconducting GeO.
• Excitonic gaps were calculated at 6.24 eV (deep UV) for GeO₂ and 3.10 eV (visible) for GeO, indicating strong light-matter interactions and high reflectivity.

Conclusions:

• The study successfully identified and characterized hexagonal GeO₂ and GeO phases using DFT and GW-BSE methods.
• Distinct vibrational and optical properties confirm the unique nature of each phase.
• The predicted excitonic properties suggest potential for optoelectronic applications, particularly in deep UV and visible light interactions.