We investigated the formation dynamics of excitons and electron-hole ($e\mathrm{\text{−}}h$) droplets (EHDs) in Si by using broadband terahertz time-domain spectroscopy. The formation of indirect excitons in Si was studied by observing their $1S\mathrm{\text{−}}2P$ transition. Changes in surface plasmon resonance of the EHDs showed a gradual condensation from homogeneous $e\mathrm{\text{−}}h$ plasma at $e\mathrm{\text{−}}h$ densities above the exciton-Mott transition. Excitonic correlations were shown to exist prior to EHD condensation even above the Mott density.

• Received 23 February 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.057401