Infrared reflection of ion-implanted GaAs

Abstract

Gallium arsenide has been implanted with nitrogen ions at 1–3 MeV and fluences between 3.3×10¹³ and 2.0×10¹⁷ ions/cm². Room‐temperature infrared spectra are presented which show major changes in the reststrahl region. A sample having the highest fluence was isochronally annealed with 2‐h 100°C steps from 200 to 600°C, and the implantation‐induced reflectivity changes are annealed by 600°C. Changes of the dispersion parameters were determined by Kramers‐Kronig analysis as well as by curve fitting with classical dispersion (CD) analysis. Examples of dispersion parameters obtained by different analyses are compared and their validity is discussed. The data of nonimplanted and samples implanted with fluence up to 3.3×10¹⁴ ions/cm² can be satisfactorily fitted with CD analysis assuming the material to be optically homogeneous. With this assumption, attempts to fit the data of samples with fluences ≥3.3 ×10¹⁵ ions/cm² were unsuccessful. By extending the CD analysis to a layer model a reasonable fit was achieved. The analyses indicate changes in the transverse‐ and longitudinal‐optic‐mode frequencies. The latter changes were confirmed by Raman scattering measurements. Both the analyses and interference fringes observed in the near‐infrared reflection spectra indicate some implantation‐induced increase in the high‐frequency dielectric constant.