Photon-field-shape effects on Rabi splitting energies in ZnO microcavities

•We fabricate ZnO microcavities with HfO2/SiO2 distributed Bragg reflectors.•The photon-field shape in the cavity is tuned to node or anti-node type.•The cavity-polariton dispersions are confirmed by angle-resolved reflectance.•The Rabi splitting energies are analyzed from the cavity-polariton dispersion.•The Rabi splitting energies are controlled by the photon-field shape. We have investigated the photon-field-shape effect on the Rabi splitting energies in ZnO microcavities with HfO2/SiO2 distributed Bragg reflectors (DBRs). The thickness of the ZnO active layer was fixed to λ/2 corresponding to a half of an effective resonant wavelength of the lowest-lying exciton. The photon-field shape was tuned to a node type or an antinode type by changing the order of the refractive indices in the DBRs. We obtained the cavity-polariton dispersions from angle-resolved reflectance spectra measured at 10K. The Rabi splitting energies were evaluated from the analysis of the cavity-polariton dispersions with a phenomenological Hamiltonian for the strong coupling between the three kinds of excitons peculiar to ZnO labeled A, B, and C and the cavity photon. It was found that the Rabi splitting energies in the antinode-type microcavity are almost a half of those in the node-type microcavity. We semi-quantitatively analyzed the photon-field-shape effect, taking account of the overlap between the exciton and photon-field envelope functions.