Ultrafast recombination processes in lead chalcogenide semiconductors studied via picosecond optical nonlinearities.

Picosecond recombination processes of photoexcited electron-hole plasma in lead chalcogenides are directly monitored via time-resolved pump-probe experiments at wavelengths from 3 to 10 Mym. Bleaching of the interband absorption due to band filling gives rise to a large change in the refractive index. The time-resolved change of absorption of PbSe at T is equal to 70 K reveals a rapid recombination within 100 ps for excitation densities above 7 x 10high17 cmhighminus3. Comparative measurements of mid-infrared luminescence spectra demonstrate that this behaviour is due to recombination by stimulated emission. At T is equal to 300 K, Auger recombination on a time scale of 2 ns is observed below the threshold of stimulated emission. The analysis of the time- resolved data gives an Auger coefficient of 1.1 plusminus 0.3 x 10highminus28 cmhigh6 shighminus1 for a carrier density of 3 x 10high18 cmhighminus3.