Optical properties of ion-implanted GaAs: The observation of finite-size effects in GaAs microcrystals

Abstract

We have carried out reflectivity measurements, for photon energies from 2.0 to 5.6 eV in the electronic interband regime, for a series of unannealed ion-implanted GaAs samples which had been exposed to 45-keV ${\mathrm{Be}}^{+}$ ions at various fluences up to 5×${10}^{14}$ ions/${\mathrm{cm}}^2$. The microstructure of the near-surface implantation-induced damage layer in these samples is known (from previous Raman work) to consist of a fine-grain mixture of amorphous GaAs and GaAs microcrystals, with the characteristic microcrystal size L of the microcrystalline component decreasing with increasing fluence (L=55 Å at 5×${10}^{14}$ ${\mathrm{cm}}^{\mathrm{-}2}$). The optical dielectric function of each sample’s damage layer has been derived from the observed reflectivity spectrum by Lorentz-oscillator analysis. Then, by inverting the effective-medium approximation, we have extracted the dielectric function of the microcrystalline component (μ-GaAs) within the damage layer.