Observation of Fe-related defects in neutron irradiated semi-insulating InP

Optical absorption and positron lifetime measurements have been performed o n Fe-doped semi-insulating InP single crystals irradiated with thermal neut rons in a wide dose range from 0.1 to 2.7 x 10(17) n cm(-2). Two lifetimes were found: tau (1) = 210 ps is constant in all the irradiation range; and tau (2) = 340 ps reaches an intensity of almost 40% at the higher fluence u sed. When comparing these results with those obtained on unintentionally do ped InP, a large increase of the longest lifetime is observed, from 300 ps in the nondoped InP to 340 ps in the semi-insulating InP. The increase of t he second lifetime in InP:Fe means that the positron traps are less attract ive to positrons. These positron traps have been associated to a complex de fect generated by the main neutron-originated defect, the indium vacancy, a nd the clusters or interstitial atoms of Fe. The optical absorption spectra show a background absorption related to Fe precipitates in as-grown InP:Fe . This background absorption disappears after neutron irradiation, suggesti ng the destruction of Fe precipitates by the energetic particles generated in the transmutation process of In-115. (C) 2001 American Institute of Phys ics.