The material state of ion-implanted Cr in GaAs

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Abstract
Chromium-implanted GaAs has been studied using 120 keV implants to fluence levels from 1×1014 to 5×1016 cm−2. The postannealed materials state has been examined using Rutherford backscattering spectrometry, proton-induced x-ray excitation, channeling, and transmission electron microscopy. Annealing was performed in flowing H2 at 900 C for 15 min under 85-nm thick Si3N4 dielectric caps. Various stages of precipitation were observed having structure and composition that depended on total implanted fluence. For the highest fluence, coarse nonuniform second-phase precipitates were present with dimensions on the order of 50 to 100 nm. At lower fluences small defect cluster precipitates, with average diameters of 6 nm, were identified through black-white contrast analysis. The relative fraction of precipitated Cr was 40% at 1×1015 cm−2 and decreased to 9% at 5×1014 cm−2. The volume concentration of implanted Cr that is retained in solid solution after annealing is estimated at 2×1018 cm−3. Channeling analysis suggests that these atoms are retained in nonunique interstitial or other nonsubstitutional positions.