Ion-implanted nitrogen in gallium arsenide

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 N_As,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 ${\text{φ\hspace{0.17em}[inverted lazy s]\hspace{0.17em}10}}^{17}\hspace{0.17em}\mathrm{ions}/{\mathrm{cm}}^2$ 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 ${\text{φ≲10}}^{17}\hspace{0.17em}{\mathrm{ions\; cm}}^{\text{−2}}$ showed no appreciable change in I up to 873 °K. The short‐range disorder in the ${\text{φ≳1×10}}^{17}\hspace{0.17em}{\mathrm{ions\; cm}}^{\text{−2}}$ 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.