Photoluminescence Of Biexcitons And Bound Biexcitons From Cucl Thin Films

We have investigated the photoluminescence (PL) properties of CuCl thin films grown by a vacuum deposition under a high-density-excitation conditions with a pulsed nitrogen laser. We have clearly observed the PL band with superlinear excitation-power dependence in the low-energy side of the free-biexciton band. This band has two characteristics with the excitation-power dependence: The intensity exhibits the saturation behavior before the remarkable growth of the free-biexciton band, and the peak energy does not change. From these facts, we conclude that the origin is the bound biexciton: The binding energy is estimated to be 45 +/- 2 meV. In addition, we discuss the thermal stability of the bound biexciton from the temperature dependence of the PL spectra. We find that the thermal stability of the bound biexciton is similar to that of the bound exciton with the lowest binding energy of the exciton complexes.