Ab-initio study of oxygen vacancies in alpha-quartz

TL;DR

This study uses ab initio calculations to analyze oxygen vacancies in alpha-quartz, revealing their stable charge states, associated geometries, and optical transition energies, which are relevant for understanding defect-related optical properties.

Contribution

It provides detailed ab initio insights into the formation energies, charge states, and optical transitions of oxygen vacancies in alpha-quartz, a novel comprehensive analysis.

Findings

Oxygen vacancies are stable in multiple charge states including +3, 0, -2, -3.

Large asymmetric distortions stabilize charged vacancy states.

Optical transitions are predicted at around 3 eV, 6.5 eV, and 2.5-3.0 eV depending on charge state.

Abstract

Extrinsic levels, formation energies, and relaxation geometries are calculated ab initio for oxygen vacancies in alpha-quartz SiO2. The vacancy is found to be thermodynamically stable in the charge states Q=+3, Q=0, Q=--2, and Q=-3. The charged states are stabilized by large and asymmetric distortions near the vacancy site. Concurrently, Franck-Condon shifts for absorption and recombination related to these states are found to be strongly asymmetric. In undoped quartz, the ground state of the vacancy is the neutral charge state, while for moderate p-type and n-type doping, the +3 and -3 states are favored, respectively, over a wide Fermi level window. Optical transitions related to the vacancy are predicted at around 3 eV and 6.5 eV (absorption) and 2.5 to 3.0 eV (emission), depending on the charge state of the ground state.