Observation of coherent biexcitons in ZnO/ZnMgO multiple quantum wells at room temperature

We have studied ZnOZnMgO multiple quantum wells by spectrally resolved transient four-wave mixing with both one- and two-color excitations. The presence of an extended signal at negative interpulse delays in the two-color experiment is attributed to the two-photon coherence resulting from the generation of biexcitons. This technique provides a means to observe a transient four-wave mixing from biexcitons in the absence of any other signal, and thereby provides the first clear evidence that biexcitons are present in narrow ZnOZnMgO quantum wells at room temperature. Dephasing times of the order of 100 fs for the biexcitons are measured.