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 λ/32 to λ/4, while the cavity length was fixed at λ/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 λ/32 to λ/4. The active-layer-thickness dependence of the Rabi splitting energy is quantitatively explained by a simple theory for quantum-well microcavities.

We have investigated the characteristics of the exciton polaritons in a ZnO microcavity. The microcavity consists of an effective one-wavelength thick ZnO active layer and HfO 2 /SiO 2 distributed Bragg reflectors (DBRs) at the bottom and top. We adopted rf magnetron sputtering and pulsed laser deposition for the preparation of the DBR and ZnO layer, respectively. Angle-resolved reflectance and photoluminescence spectra demonstrate the formation of the cavity polaritons. The cavity polariton dispersions are analyzed using a phenomenological Hamiltonian for the coupling between the cavity photon and three kinds of fundamental excitons labeled A, B, and C. The vacuum Rabi splitting energy is estimated to be $80 meV. The giant Rabi splitting energy reflects the large exciton oscillator strength of ZnO.Semiconductor microcavities have attracted much attention from the aspect of controlling the optical responses of exciton polaritons in a strong exciton-photon coupling regime resulting in the formation of cavity polaritons. 1) The prominent applications of cavity polaritons are polariton lasing, 2,3) parametric polariton amplifiers, 4,5) Bose-Einstein condensation of polaritons, 6,7) and enhancement of entangled-photon generation, 8) which are attractive in semiconductor physics. Until now, GaAs-based microcavities have been major samples owing to the well-established method for the sample preparation using molecular beam epitaxy or metal-organic chemical vapor deposition (MOCVD). Recently, microcavities consisting of wide-gap semiconductors such as GaN 9-11) and ZnO 12,13) have been developed from the viewpoint of large exciton binding energies, 28 meV for GaN 14) and 61 meV for ZnO, 15) leading to the high stability of the excitonic system.In this letter, we report on the fabrication of a ZnO-based microcavity with distributed Bragg reflectors (DBRs) and the observation of cavity polaritons. Note that the preparation method for the ZnO-based microcavity has not yet been established, which is mainly due to the problem of the fabrication of DBRs suitable for ZnO. In ref. 12, ZrO 2 /MgO DBRs were prepared by pulsed laser deposition (PLD). On the other hand, in ref. 13, bottom and top DBRs were AlGaN/GaN and SiO 2 /Si 3 N 4 systems grown by MOCVD and remote plasma enhanced CVD, respectively. In the present work, we adopted rf magnetron sputtering for the preparation of HfO 2 /SiO 2 DBRs at the bottom and top of the microcavity because the sputtering method is convenient and powerful for the deposition of oxide materials. For the ZnO active layer, we used PLD to grow a high quality film. The cavity polaritons were observed with angleresolved reflectance spectroscopy and photoluminescence (PL) spectroscopy. The experimental results were analyzed by calculating the cavity polariton dispersions with a phenomenological Hamiltonian for the coupling between the cavity photon and excitons, where we consider the A, B, and C excitons peculiar to ZnO. In the earlier works on ZnO-based microcavities, 12,13) such a precise analysis ...

No abstract

We have investigated the characteristics of exciton polaritons in ZnO microcavities with different active layer thicknesses. The microcavity was made from a bulk ZnO active layer and two distributed Bragg reflectors (DBRs) consisting of HfO 2 and SiO 2 layers. We adopted rf magnetron sputtering and pulsed laser deposition for the preparation of the DBR and ZnO active layer, respectively. Angle-resolved reflectance spectra demonstrate the formation of cavity polaritons. From the analysis using a phenomenological Hamiltonian for the coupling between the cavity photon and three kinds of excitons labeled A, B, and C peculiar to ZnO, the vacuum Rabi-splitting energies in the l/2-microcavity are estimated to be 30, 71, and 84 meV for the A, B, and C excitons, respectively. Moreover, we indicate the potential to control the Rabi-splitting energy by changing the active layer thickness.

No abstract