Optical dephasing and excitation transfer of an impurity-bound exciton in a semiconductor: Photon-echo experiments on GaP:N

We report low-temperature results of accumulated and two-pulse picosecond photon-echo experiments on the optical transition of the nitrogen-bound exciton in GaP:N. The observed temperature dependence of the dephasing of the so-called A line at 534.95 nm can be explained in terms of (stimulated) phonon processes involving the lower B state and, at higher temperatures, the free-exciton band. The low-temperature-echo decay time of 25.5±{}0.5 ps is shown to be determined by the lifetime of a A state. Analysis of the factors governing the intensity of the accumulated photon echo as a function of temperature leads to the conclusion that in the B state temperature-independent excitation transfer occurs. The rate constant of this phenomenon, which we ascribe to excitation tunneling, is 10⁷ s^-1.