Near normal incidence reflection and transmission measurements of GaAs and GaP samples implanted with large doses of sim;3hyphen;MeV ions of31P+or14N+showed frequencyhyphen;dependent maxima and minima in the frequency range 800lsim;ngr;lsim;7500 cmminus;1. Assuming a layer model for the implanted material and considering reflections from layers surfaces, the interference fringes are analyzed to obtain the refractive index and thickness of both the cover and buried layers and substrate. With the same layer model the changes in the GaAs reststrahlen are shown to be quantitatively compatible with the results of the fringe measurements. Annealing GaAs at temperatures lsim;400thinsp;deg;C reduced the implantationhyphen;induced changes in the refractive index but the layer thicknesses remained constant. There was no evidence for regrowth by motion of the implanthyphen;substrate interface as has been reported for silicon crystals. The analysis of the reststrahlen data for GaP is less satisfactory since the data could not be closely fitted with any choice of parameters.
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