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

dc.contributorVirginia Techen
dc.contributor.authorFeng, G. F.en
dc.contributor.authorZallen, Richard H.en
dc.description.abstractWe 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 Be+ ions at various fluences up to 5×1014 ions/cm2. 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 5×1014 cm-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. The optical properties of μ-GaAs differ appreciably from those of the bulk crystal, the difference increasing with decreasing L. We find that the microcrystallinity-induced spectral changes are concentrated in the linewidths of the prominent interband features E1, E1+Δ1, and E2. These linewidths increase linearly and rapidly with inverse microcrystal size: Γμ=Γ0+AL-1, where Γ0 is the linewidth in the bulk crystal, Γμ is the linewidth in μ-GaAs, and A is a constant. For the E1 and E2 peaks, the experimentally determined value of A is such that the finite-size broadening (AL-1) is about 0.2 eV when L=100 Å. We propose a simple theory of the finite-size effects which, when combined with band-structure information for GaAs, semiquantitatively accounts for our observations. Small microcrystal size implies a short time for an excited carrier to reach, and be scattered by, the microcrystal boundary, thus limiting the excited-state lifetime and broadening the excited-state energy. An alternative uncertainty-principle argument is also given in terms of the confinement-induced k-space broadening of electron states.en
dc.description.sponsorshipTexas Instrumentsen
dc.description.sponsorshipVirginia Center for Innovative Technologyen
dc.identifier.citationFeng, G. F.; Zallen, R., "Optical properties of ion-implanted GaAs: The observation of finite-size effects in GaAs microcrystals," Phys. Rev. B 40, 1064 DOI: http://dx.doi.org/10.1103/PhysRevB.40.1064en
dc.publisherAmerican Physical Societyen
dc.rightsIn Copyrighten
dc.subjectphysics, condensed matteren
dc.titleOptical properties of ion-implanted GaAs: The observation of finite-size effects in GaAs microcrystalsen
dc.title.serialPhysical Review Ben
dc.typeArticle - Refereeden


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