Magnesium Concentration Dependence of Room-Temperature Absorption-Edge Singularity in Alloyed MgZnO Epilayers

Abstract

Recently, the absorption-edge singularity model accounting for the interaction between excess electrons and photocreated holes has been applied to room-temperature optical spectra in n-type ZnO epilayers [T. Makino et al.: Phys. Rev. B 65 (2002) 121201(R)]. This model predicts that the onset of the spectrum should exhibit a power-law singularity of the form [(E-E₁)^-α] with the threshold energy of E₁ located near the fundamental gap. The results of our fitting using this model are in fairly good agreement with available experimental data obtained for MgZnO thin films, which were reported by Kang et al. [Solid State Commun. 115 (2000) 127]. The power exponent α, which is related to the magnitude of screening between photocreated carriers relative to that provided by excess electrons, was enhanced with the incorporation of Mg and had a maximum at the Mg concentration of 8%. The possible reasons for this enhancement are discussed.