Dynamics of newly observed biexcitons in ZnO epitaxial thin films

Recently, photoluminescence (PL) due to a biexciton state was observed in high-quality ZnO epitaxial thin films. Dynamics of the biexcitons was studied by measuring time-resolved PL intensity. Temporal behaviors of the PL intensity of the biexcitons and free excitons can be explained by modified rate equations on the assumption that the creation rate of the biexcitons is proportional to the 1.5th power of exciton density. This dependence is consistent with the experimental results that the biexciton PL intensity is proportional to the 1.5th power of the excitation density.