Formation and Decay of Electron-Hole Plasma Clusters in a Direct-Gap Semiconductor CuCl

The master equation for the cluster-size distribution function is solved numerically to investigate the electron-hole droplet formation claimed to be discovered in the direct-gap CuCl excited by picosecond laser pulses Nagai et al Phys. Rev. Lett. 86 (2001) 5795; J. Lumin. 100 (2002) 233. Our result shows that for the excitation in the experiment, the average number of pairs per cluster (ANPC) is only around 5.2, much smaller than that (10⁶ typically for Ge) of the well studied electron-hole droplet in indirect-gap semiconductors such as Ge and Si. These results indicate that what measured in CuCl by Nagai et al. may not come from the EHD formed from exciton gas, instead possibly come from some bubbles of excitons in metallic liquid.