Optical properties of anodically degraded ZnO
We discuss the optical properties of non-degraded and anodically degraded boron-doped zinc oxide (ZnO:B) deposited by low-pressure chemical vapour deposition on soda-lime glass. The optical model used to simulate the infrared reflectance in the wavelength range between 1.2 and 25 mu m is based on the Maxwell-Garnett effective-medium theory. The model is sensitive to the conditions at the grain boundaries of the investigated polycrystalline ZnO: B films. We confirm that the presence of defect-rich grain boundaries, especially after degradation, causes a highly resistive ZnO: B film. Furthermore, indications of a degraded zinc oxide layer next to the ZnO:B/glass interface with different refractive index are found. We present evidence for the creation of oxygen vacancies, based on Raman investigations, which correlate with a shift of the optical absorption edge of the ZnO: B. Investigations with scanning and transmission electron microscopy show microvoids at the grain boundaries after anodic degradation. This indicates that the grain/grain interfaces are the principle location of defects after degradation. (C) 2014 AIP Publishing LLC.