FAST RECOMBINATION PROCESSES IN LEAD CHALCOGENIDE SEMICONDUCTORS STUDIED VIA TRANSIENT OPTICAL NONLINEARITIES

Third-order optical nonlinearities and recombination processes of photoexcited electron-hole plasma in PbSe and PbTe are directly monitored by picosecond pump-probe experiments in the wavelength range from 3 to 10 μm. After excitation, a strong blue shift of the absorption edge and large changes of the refractive index are found. Time-resolved studies of the absorption changes at lattice temperatures between 70 and 160 K reveal a fast partial decrease of the carrier density within 100 ps at excitation densities exceeding 7×1017 cm-3. Comparative emission spectra demonstrate that this behavior is due to recombination by stimulated emission. At room temperature the nonradiative Auger recombination dominates on a 0.5-2 ns time scale below the threshold of stimulated emission. The overall Auger coefficients for carrier densities of about 1018 cm-3 are derived from the data and have values of cAPbSe=1. 1±0.3×10-28 cm6/s and cA PbTe=2.5±1.3×10-28 cm6/s. © 1995 American Institute of Physics.