Optical absorption and electronic structure of Zn1-xMnxO alloys studied by spectroscopic ellipsometry

Dielectric functions of Zn1-xMnxO (xless than or equal to0.19) thin films were obtained by spectroscopic ellipsometry at room temperature in the 1.5-5 eV photon energy region. A strong absorption structure is observed near 3.1 eV, below the optical band-gap absorption (E-0) edge, and it does not shift with x. It is interpreted as due to transitions between the crystal-field-split 3d(5) multiplet levels of the tetrahedral Mn2+ ion that substitute for Zn2+. A redshift is observed for the E-0 edge near x=0.06 from that of pure ZnO, interpreted as due to the spin-exchange interaction between d electrons of the Mn2+ ion and sp electrons near the band gap. The E-0 edge shows a blueshift for larger x. The excitonic character of the E-0 edge is gradually reduced and replaced by a three-dimensional shape as x increases, and this is attributed to increased disorder. (C) 2003 American Institute of Physics.