Saturation spectroscopy of bound excitons in GaP:N

Saturation hole burning has been used to determine the homogeneous linewidth in the liquid helium temperature range of the lowest-energy transition of excitons bound at isoelectronic nitrogen defect centres in GaP. The defects involved are pairs of nitrogen atoms in nearest-neighbour phosphorus sites. The homogeneous linewidths ( Gamma h >70 MHz) are approximately three orders of magnitude greater than the limit set by population decay. The temperature dependence of Gamma h is consistent with a dephasing process dominated by one-phonon-induced transitions to nearby higher bound exciton levels.