Effects of nitrogen/oxygen on the electrical and optical properties and microstructure of triple layer AZO/Ag/AZO thin films

Abstract

Aluminum-doped zinc oxide (AZO)/Ag/aluminum-doped zinc oxide (AAA) specimens are prepared by varying O2 and N2 flow rates during the AZO deposition to investigate the gas effects on surface morphology, microstructure, conductivity type and optical and electrical properties. The AZO specimens are found to have decreases in grain size and RMS surface roughness (SRq), and an increase in compressive residual stress when the N2 flow rate increases higher than 2.5 sccm. The addition of O2 can contribute a similar tendency to grain size, SRq and residual stress; the grain size and SRq are always comparatively smaller, while the residual stress is higher than that prepared with N2. The grain size and SRq are obtained to be proportional to the AZO thickness, whereas they are inversely proportional to the compressive residual stress of AZO. Specimen D prepared with (N2: 0, O2: 2.5) sccm and having 60-nm AZO thickness possesses the strongest anti-reflection effect of the AAA structure, and therefore impedes the reflection from the Ag interlayer significantly. P-type conductivity is achieved by introducing the N2 into the AZO layers and (N2: 15, O2: 0) sccm is used to achieved the highest carrier concentration (CC) and mobility (Mb), and thus the lowest resistivity (R) of all specimens in this study. Increasing the O2 flow rate leads to decreases in Mb and CC, but can obtain the highest average transmittance ( T ¯ ) as (N2: 0, O2: 2.5) sccm is applied. The O2 flow rate becomes the dominant factor for the electrical and optical properties and microstructure as AZO films are deposited in the N2 and O2 mixed atmosphere. (N2: 15, O2: 0) sccm is used to achieve the highest CC and the lowest R of the oxide/metal/oxide specimens reported in the literatures.