Clarification of the relative magnitude of exciton binding energies in ZnO and SnO2

Abstract

ZnO and SnO2 are wide bandgap semiconductors, which have great potential for UV detectors, light emitting diodes, and other optoelectronic devices. The performance of these devices is significantly affected by exciton binding energies of oxides. Although bandgaps of ZnO and SnO2 are similar, their exciton binding energies differ by a large amount, because it was reported experimentally that the exciton binding energy of SnO2 is 130 meV, which is higher than that of ZnO with 60 meV. On the other hand, because ZnO has higher ionicity and a large overlap of electrons and hole wavefunctions, it is expected that it should have larger exciton binding energy than that of SnO2 [Dvorak et al., Phys. Rev. Lett. 110, 016402 (2013)]. Therefore, there is a controversy for relative magnitudes of the exciton binding energy between SnO2 and ZnO. Here, based on accurate GW + Bethe–Salpeter equation calculations, we clarify that the exciton binding energy of SnO2 is less than that of ZnO, following the general rule; therefore, more experimental study should be carried out to verify our predictions. We expect that this fundamental understanding of the relative magnitude of exciton binding energies will be useful for prospective applications of ZnO and SnO2 in optoelectronic devices.