We have investigated the active-layer-thickness dependence of exciton-photon interactions in planar CuCl microcavities with HfO${}_2/$SiO${}_2$ distributed Bragg reflectors. The active layer thickness was changed from $\lambda /$32 to $\lambda /$4, while the cavity length was fixed at $\lambda /$2. We performed angle-resolved reflectance measurements and clearly detected three cavity-polariton modes, originating from the lower, middle, and upper polariton branches, in a strong-coupling regime of the $Z_3$ and $Z_{1,2}$ excitons and cavity photon. The incidence-angle dependence of the cavity-polariton modes was analyzed using a phenomenological Hamiltonian for the strong coupling. It was found that the interaction energies of the cavity-polariton modes, the so-called vacuum Rabi splitting energies, are systematically controlled from 22(37) to 71(124) meV for the $Z_3$($Z_{1,2}$) exciton by changing the active layer thickness from $\lambda /$32 to $\lambda /$4. The active-layer-thickness dependence of the Rabi splitting energy is quantitatively explained by a simple theory for quantum-well microcavities.

• Received 18 October 2010

DOI:https://doi.org/10.1103/PhysRevB.83.075318