Optical absorption and positron lifetime measurements were performed on Fe-doped semi-insulating single crystals which had been irradiated with thermal neutrons to doses ranging from 1016 to 2.7 x 1017/cm2. Two lifetimes were found: one (210ps) was constant over the entire dosage range, and the other (340ps) attained an intensity of almost 40% at higher fluences. Upon comparing these results with those obtained on unintentionally doped samples, a large increase in the longest lifetime was observed (from 300ps in undoped material, to 340ps in semi-insulating material). The increase in the second lifetime, in Fe-doped samples, suggested that the positron traps were less attractive to positrons. Such positron traps were associated with a complex defect that was generated by the main neutron-induced defect (the In vacancy) and clusters or interstitial atoms of Fe. The optical absorption spectra indicated a background absorption which was related to Fe precipitates in as-grown Fe-doped samples. This background absorption had disappeared after neutron irradiation; thus implying the destruction of Fe precipitates by energetic particles which were generated by the transmutation of 115In.

Observation of Fe-Related Defects in Neutron Irradiated Semi-Insulating InP. B.Marí, M.A.Hernández-Fenollosa, F.J.Navarro: Journal of Applied Physics, 2001, 89[12], 7772-6