ABSTRACTThe damage layer in unannealed Be+-implanted GaAs samples (45-keV Be+ ions, 1013 to 5 × 1014 ions/cm2) consists 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. We have carried out reflectivity measurements on these samples for photon energies from 2.0 to 5.6 eV, in the electronic interband regime. Using Lorentz oscillator analysis and the effective medium approximation, we have extracted the dielectric function of the microcrystalline component (μ-GaAs) within the damage layer. The optical properties of μ-GaAs deviate appreciably from those of the bulk crystal near the interband absorption peaks. The linevidths of these peaks are found to increase over the bulk-crystal value by an amount proportional to (l/L), the increase being about 0.2 eV when L =100 Å. These finite-size effects can be understood in terms of a lifetime reduction caused by the short time it takes for electrons to reach the microcrystal boundaries.
Optical properties of ion-implanted GaAs: The observation of finite-size effects in GaAs microcrystals
