Active optical modulation in hybrid transparent-conductive oxide/electro-optic multilayers

We report the room temperature, low-voltage-enabled modulation of the optical response of hybrid transparent-conductive-oxide/ferroelectric multilayers. We have fabricated an optical multilayer consisting of Al-doped ZnO (AZO) and BaTiO3 films deposited on a Nb-doped SrTiO3(110) substrate. Applying a low voltage between the AZO film and the substrate, a significant variation of the system's optical response has been detected by means of in operando spectroscopic ellipsometry. The voltage-induced variations have been ascribed to a combination of charge accumulation/depletion at the insulator/semiconductor interface and the field-induced Pockels effect in the BaTiO3 layer and successfully reproduced by an optical model including these effects. We have deduced a variation of the refractive index in AZO in the infrared range by more than 0.1 at an applied bias of 0.2 V and by more than 2 at an applied bias of just 3 V at room temperature, which can be strongly appealing for voltage-modulated active optical systems.