Spectral and intensity dependence of spatially resolved two-photon conductivity defects on a GaAsP photodiode

Femtosecond laser excitation through a near-field scanning optical microsco pe is used to study spatially resolved defects in the two-photon conductivi ty of a GaAs0.6P0.4 diffusion type photodiode. Two types of defects are obs erved when the photodiode is excited with femtosecond pulses below the bulk band gap energy. Photocurrent enhancement defects show a higher photocurre nt than the surrounding areas and are driven by both one-and two-photon pro cesses. These defects are often correlated with pits in the photodiode surf ace. Photocurrent depression defects have the normal two-photon power depen dence and are not associated with surface pits. Based on the low measured c overage of both defect sites, the performance of GaAsP in auto- and cross c orrelators will be unaffected in most situations. A deviation in alloy stoi chiometry, in which localized areas are rich in arsenic while poor in phosp horus, provides the best explanation for the origin of the enhancement defe cts. (C) 2001 American Institute of Physics.