Ion-implanted nitrogen in gallium arsenide

Abstract

Several gallium arsenide samples were implanted at room temperature with 14N+ ions. Infrared absorption measurements at ≃ 80 °K showed a broad band near 480 cm−1 which is attributed to the localized vibrational mode of NAs,N substitutional on an As site. Measurements were made of the dependence of the integrated absorption I on the fluence φ for 1.0 × 1016 ≤ φ ≤ 2.0 × 1017 ions/cm2, on flux from 2.4 × 1012 to 1.2 × 1013 ions/cm2 sec, and on ion energies between 1.0 and 3.0 MeV. I increases linearly with φ until φ [inverted lazy s] 1017 ions/cm2 and decreases substantially at larger fluences probably due to the presence of short-range lattice disorder. The implanted samples were annealed isochronally from 473 to 1073 °K, and isothermally at 973 °K. The isochronal anneal for φ≲1017 ions cm−2 showed no appreciable change in I up to 873 °K. The short-range disorder in the φ≳1×1017 ions cm−2 samples annealed at much lower temperature. For all φ values the I decreased substantially after 973 °K anneal and after 1073 °K the I was virtually zero. The high-temperature decrease in I is irreversible. The isothermal anneal indicates that the annealing mechanism is not simple and cannot be explained by a simple integral-order kinetic process. Ion microprobe analysis of the same sample before and after 1073 °K annealing shows nearly identical approximately Gaussian peaks in the 14N+ concentration indicating negligible out-diffusion of nitrogen. The depth and the peak are in reasonable agreement with LSS predictions. The formation of GaN after high-temperature anneal is unlikely since infrared measurements do not show the GaN characteristic lattice modes. The disappearance of the 480-cm−1 band after high-temperature annealing is tentatively attributed to the formation of N2 molecules which are infrared inactive.