Infrared reflection and Raman scattering of ion-implanted nitrogen in gallium phosphide

Abstract

Infrared reflection and Raman scattering measurements were performed on a set of GaP samples implanted at room temperature with ¹⁴N⁺ and ¹⁵N⁺ ions with an energy of 3 MeV and fluences in the range of 5×10¹³–2×10¹⁷ ions/cm². The reflection data for all but the most heavily implanted samples were fitted with a classical dispersion layer model. Some of the parameters used in this model were obtained from the Raman data. An increased in the damping constant γ is the largest implantation‐induced change in the dispersion parameters. Annealing studies were performed on several samples implanted with 2×10¹⁷ ions/cm². Raman and x‐ray measurements indicated that samples annealed at 773 °K recrystallized in a polycrystalline fashion but those annealed at 573 °K became single crystals. After both types of annealing procedure, structure resulting from the nitrogen localized vibrational mode was seen in the reflection spectra. This mode exhibited the expected isotope shift, appearing at ∼495 cm⁻¹ for samples implanted with ¹⁴N⁺ and ∼480 cm⁻¹ for samples implanted with ¹⁵N⁺. That the mode was observable only after annealing indicated that there was some reduction of the short‐range order in the unannealed samples. The results are discussed in terms of prevalent models for lattice disorder introduced by ion implantation.