The effect of Mn doping on the interband transition and band tail absorption characteristics of Mn:(Pb, Sr)TiO₃ ferroelectric thin films

Mn composition dependence of optical properties, especially interband electronic transition and band tail absorption behaviors, in Mn doped (Pb, Sr)TiO₃ (PST) films were investigated by transmittance spectroscopy. The optical parameters of Mn doped PST films in transparent region were evaluated by Cauchy model. The decrease of optical band gap and the expansion of the band tail states with the increasing of Mn dopant amount were observed. The shrinkage of optical band gap is attributed to lowering the bottom of conduction bands by Mn 3d orbitals and the decrease of lattice constant in Mn doped PST films. Meanwhile, the random occupation of Mn ion and the increase of oxygen vacancy after Mn doping are the main causes for the expansion of localized states in band tails.