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

Abstract

Femtosecond laser excitation through a near-field scanning optical microscope is used to study spatially resolved defects in the two-photon conductivity of a GaAs0.6P0.4 diffusion type photodiode. Two types of defects are observed when the photodiode is excited with femtosecond pulses below the bulk band gap energy. Photocurrent enhancement defects show a higher photocurrent than the surrounding areas and are driven by both one-and two-photon processes. These defects are often correlated with pits in the photodiode surface. Photocurrent depression defects have the normal two-photon power dependence and are not associated with surface pits. Based on the low measured coverage of both defect sites, the performance of GaAsP in auto- and cross correlators will be unaffected in most situations. A deviation in alloy stoichiometry, in which localized areas are rich in arsenic while poor in phosphorus, provides the best explanation for the origin of the enhancement defects.