Interband excitation induced absorption by deep impurities in GaP

Transient optical absorption at energies below the band gap in GaP crystals following pulsed interband excitation was observed. The additional absorption attained its maximum about 25 μsec after the excitation pulse and lasted about 100 μsec. The spectral dependence of the rise time and decay time of the absorption and that of the induced optical cross section were determined. The results suggest that the induced absorption is caused by several deep impurity levels, which are most probably due to Cu, being populated by the recombination of excited electrons.