Multichannel Mueller matrix analysis of the evolution of the microscopic roughness and texture during ZnO:Al chemical etching

Transparent conducting oxides (TCOs) are used in thin film silicon (Si:H) photovoltaics (PV) technology as top electrical contacts and as the components of back-reflecting structures. TCOs are often prepared with macroscopically rough interfaces and/or surfaces (i.e., with "texture") in order to scatter light and thereby enhance optical path lengths in the active layers of the device. Optical analysis of textured TCOs is a considerable challenge, due to the existence of surface roughness and non-uniformity over more than six orders of magnitude in the lateral scale L, from tenths of nanometers to hundreds of microns or more. In this research, we have developed the optical technique of multichannel Mueller matrix ellipsometry to extract the optical properties (ε₁, ε₂) of textured TCO films as well as the time evolution of surface roughness layer thicknesses on microscopic, macroscopic, and "geometrical optic" lateral scales during the TCO fabrication process.