New approach toward transparent and conductive ZnO by atomic layer deposition: Hydrogen plasma doping

A hydrogen plasma doping process was combined with the traditional atomic layer deposition (ALD) technique in order to enhance the transparency and conductivity of ZnO films. The hydrogen plasma was included in situ during each ALD cycle and was found to be more effective at producing highly conductive ZnO when used before the H₂O vapor pulse that is standard to thermal-ALD processes. Through the hydrogen plasma doping process, the resistivity and carrier concentration of the ALD ZnO films are improved to levels suitable for transparent conductive oxide applications. These favorable electrical properties, combined with improved transparency, make such H-doped ZnO films comparable to some of the best Al-doped ZnO materials achieved with ALD processes in the literature. At thicknesses well below 200 nm, the H-doped ALD ZnO films maintain optimal resistivities near 7 × 10^-4 Ω cm along with average transmittance values of ∼92% from 400 to 1000 nm.