Picosecond spectral hole burning in ZnCdTe layers

The spectral and temporal behavior of absorption bleaching due to band- and state-filling processes in Cd1−xZnxTe polycrystalline layers with a nominal composition x=0.17 are investigated. The absorption bleaching due to band-filling effects has a decay time in the range of 35 and 90 ps which depends on the photon energies of the pump and test beams. It is attributed to the relaxation of quasi-Fermi levels through the bottom (top) of the conduction (valence) band and corresponds to the lifetime of nonequilibrium charge carriers. The absorption bleaching due to state-filling processes corresponds to the nonthermal part of the energy distribution of free carriers and therefore depends on the photon energy of the pump beam. A hole burning is found which peaks near the photon energy of the pump laser and which follows the temporal shape of the laser pulses (20 ps). The asymmetry of the hole-burning spectrum is attributed to the energy dependence of the density of states which is important for electron–electron scattering processes.