Modulated differential reflectance as a precise tool for probing low ion fluences in implanted GaAs

Abstract

Differential reflectance spectroscopy (DR), a sensitive optical modulation technique has been applied to study ion implanted GaAs. The DR spectrum corresponds to the difference of optical reflectivity signals from implanted and unimplanted (masked) halves of a sample. In the experimental setup of the present study the sample rotates synchronously with the frequency of the lock-in amplifier. The measured signal is proportional to the difference in reflectance coefficient R. In this work the differential reflectance results for 5 keV Ar+ ion implanted (100) GaAs wafers at fluencies ranging from З*10^11 to 1*10^14 ions/cm^2 are presented. DR spectra were collected for the photon energies varying from 1.65 to 3.35 eV. Owing to the experimental conditions it was possible to obtain information about the Ei, Ei+▲, critical points of a GaAs band structure. The DR spectra show broadening in the vicinity of the critical points. Analysis of the DR spectral region near the critical points gives information about post-implantation damage's level depending on ion fluence.