ELECTRONIC-STRUCTURE OF BINARY AND TERNARY GA OR AS OXIDES

A systematic analysis of the electronic structure of AS2O3, As2O5, Ga2O3, and GaAsO4 is made both experimentally and theoretically. The comparison between x-ray-photoemission spectra and tight-binding calculations allows us to recognize the contribution of each atomic state to each experimental peak. A clear distinction between AS2O3 and all other oxides can be made. The top of the valence band is made of O 2p lone-pair states, except in AS2O3, where the main contribution comes from As 4s states which gives a sharp feature at the top of the valence band. There is no observable difference in the x-ray photoelectron spectra between tetrahedral and octahedral environments for Ga and As atoms. From the calculated electronic charges, we can define the oxidation numbers that are also identical for tetrahedral and octahedral As or Ga atoms. Total-energy calculations show that oxides like Ga2O3 with only octahedral sites have a higher formation energy than those with both octahedral and tetrahedral sites.