Variations of recombination lifetime, with fluence of the reactor neutrons from 10^{12} to 3×10^{16} n/cm^2, in the magnetic field applied Czochralski grown Si samples are examined by the contactless transient techniques of the microwave probed photoconductivity and dynamic gratings. A nearly linear decrease in lifetime from few microseconds to about 200 ps within the examined range of neutron irradiation fluences was obtained. This dependence persists under relatively low (≤80°C) temperature heat treatments. Also, cross-sectional scans of lifetime depth-profiles were examined, which show rather high homogeneity of lifetime values within wafer thickness.
The numerical analysis and experimental data on time-resolved four-wave mixing confirmed a novel origin of oscillations in subnanosecond carrier dynamics in highly excited InP:Fe crystals. The effect was attributed to simultaneous presence of electron and hole gratings, which drift in the space charge field and contribute constructively or destructively to refractive index modulation in time domain.
Role of deep impurity levels in carrier generation, transport, and recombination were investigated in bulk ZnSe:Cr and ZnTe:V:Al crystals by four-wave mixing technique. The temporal and exposure dependencies of optical nonlinearities in ZnSe:Cr evidenced an influence of Cr1+/Cr2+ states in carrier generation, exhibited very fast carrier relaxation, and revealed the presence of competing recombination mechanisms. Similar investigations in ZnTe:V:Al showed an effective carrier generation from Al-induced defect complexes as well as very fast carrier capture by Zn-vacancies.
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