The Effects of Zr Doping on the Optical, Electrical and Microstructural Properties of Thin ZnO Films Deposited by Atomic Layer Deposition.

Transparent conducting oxides (TCOs), with high optical transparency (≥85%) and low electrical resistivity (10 ^-4 Ω·cm) are used in a wide variety of commercial devices. There is growing interest in replacing conventional TCOs such as indium tin oxide with lower cost, earth abundant materials. In the current study, we dope Zr into thin ZnO films grown by atomic layer deposition (ALD) to target properties of an efficient TCO. The effects of doping (0-10 at.% Zr) were investigated for ~100 nm thick films and the effect of thickness on the properties was investigated for 50-250 nm thick films. The addition of Zr ⁴⁺ ions acting as electron donors showed reduced resistivity (1.44 × 10 ^-3 Ω·cm), increased carrier density (3.81 × 10 ²⁰ cm ^-3 ), and increased optical gap (3.5 eV) with 4.8 at.% doping. The increase of film thickness to 250 nm reduced the electron carrier/photon scattering leading to a further reduction of resistivity to 7.5 × 10 ^-4 Ω·cm and an average optical transparency in the visible/near infrared (IR) range up to 91%. The improved n-type properties of ZnO: Zr films are promising for TCO applications after reaching the targets for high carrier density (>10 ²⁰ cm ^-3 ), low resistivity in the order of 10 ^-4 Ω·cm and high optical transparency (≥85%).