Auger recombination dynamics of lead salts under picosecond free-electron-laser excitation

Pump-probe transmission experiments have been performed on PbSe above the fundamental absorption edge near 4 μm in the temperature range 30 to 300 K, using the Dutch ps free-electron laser. For temperatures below 200 K and carrier densities above the threshold for stimulated emission, stimulated recombination represents the most efficient recombination mechanism with relatively fast kinetics in the 50–100-ps regime, in good agreement with earlier reports of photoluminescent emission. Above this temperature Auger recombination dominates, and the Auger coefficient C is determined from the pump-probe decay curves. In the low-temperature regime the Auger coefficient is determined from the decay curves at times beyond 100 ps. The Auger coefficient is approximately constant (with a value of about $8\times {10}^{-28}\hspace{0.5em}{\mathrm{cm}}^6{\mathrm{}\mathrm{s}}^{\mathrm{-}1})$ between 300 and 70 K, and then drops a value of about $1\times {10}^{-28}\hspace{0.5em}{\mathrm{cm}}^6{\mathrm{}\mathrm{s}}^{\mathrm{-}1}$ at 30 K, in good agreement with the theory for nonparabolic near-mirror bands and nondegenerate statistics. It is found that C for PbSe is between one and two orders of magnitude lower than for ${\mathrm{Hg}}_{1-x}{\mathrm{Cd}}_x\mathrm{Te}$ of comparable band gap.