Effect of stoichiometric vacancies on the structure and properties of the Ga2SeTe2 compound semiconductor

Ga2SeTe2 belongs to a family of materials with large intrinsic vacancy concentrations that are being actively studied due to their potential for diverse applications that include thermoelectrics and phase-change memory. In this article, the Ga2SeTe2 structure is investigated via synchrotron x-ray diffraction, electron microscopy, and x-ray absorption experiments. Diffraction and microscopy measurements showed that the extent of vacancy ordering in Ga2SeTe2 is highly dependent on thermal annealing. It is posited that stoichiometric vacancies play a role in local atomic distortions in Ga2SeTe2 (based on the fine structure signals in the collected x-ray absorption spectra). The effect of vacancy ordering on Ga2SeTe2 material properties is also examined through band gap and Hall effect measurements, which reveal that the Ga2SeTe2 band gap redshifts by ~0.05 eV as the vacancies order and accompanied by gains in charge carrier mobility. The results serve as an encouraging example of altering material properties via intrinsic structural rearrangement as opposed to extrinsic means such as doping.