Breaking of Raman selection rules in Cu2O by intrinsic point defects

The semiconductor cuprous oxide crystallizes in a simple cubic structure and reveals outstanding characteristics: Independent of the method and conditions of the synthesis of crystalline Cu 2 O its Raman spectra are dominated by infrared active, silent, and defect modes rather than by Raman allowed phonon modes only. A detailed group theoretical analysis demonstrates that point defects reduce the local symmetry, lift the Raman selection rules, and thus diminish the distinction between Raman allowed and Raman forbidden lattice vibrations. Of all intrinsic defects only the presence of the copper vacancy in the so called split configuration introduces possible Raman activity for all Cu 2 O extended phonon modes observed in experiment.