Beschreibung:
We report on the occupation of the lower exciton–polariton branchin a ZnO-based microcavity as a function of the detuning between the excitonand the uncoupled cavity-photon mode and on the optical excitation density.We emphasize the difference in the dispersion and occupation of the lowerpolariton branch as a function of the linear polarization of the emitted light.For the negative detuning regime, we found an energy splitting between thetransverse electric (TE)- and transverse magnetic (TM)-polarized states at inplanewave vectors between 0.4×107 m−1 and 1.2×107 m−1, which is causedby the polarization dependence of the dispersion of the uncoupled cavity-photonmode. The maximum energy splitting of about 6 meV was observed for adetuning of about 1 = −70 meV. From the integrated photoluminescence peak,we deduce the occupation of the lower polariton branch as well as the scatteringrates of exciton–polaritons into the lower polariton branch. We found that theenergy splitting causes an enhanced scattering of exciton–polaritons intothe lower polariton branch for the TM-polarized light compared with that of theTE-polarized light. By varying the excitation density, we observe a superlineargrowth of the lower polariton branch occupation for negative and intermediatedetuning regimes. For an accumulation of exciton–polaritons in the ground stateat low temperatures (T = 10 K), we found an intermediate detuning regime(−20 meV < 1 < +20 meV) as the optimum. With increasing temperature, thisoptimum detuning range shifts to larger negative values.