At a textured interface between two substances with different refractive indexes, a part of the incident light gets scattered, and the rest remains specular. Textured interfaces are an integral part of many optoelectronic devices, where light scattering is desirable. It is therefore important that we can determine optical properties of textured layers, forming textured interfaces with their adjacent layers, with various measuring techniques. In this master's thesis we deal with optical characterization of rough samples.
First we describe the basic characteristics of textured interfaces. Depending on the typical feature size within the texture, we can divide them into nano-textured and micro-textured interfaces. Nano-textured transparent conductive oxides (TCO) are an integral part of thin-film optoelectronic devices, such as thin-film solar cells, whereas micro-textured surfaces of many different substances are used as various light diffusers and reflectors. We present statistical parameters to describe the morphology of random nano-textured surfaces. We then describe two types of TCO samples (SnO2:F} Asahi U type sample and a set of ZnO:Al samples), that we have optically characterized. We also describe and optically characterize a set of micro-textured plexiglass UV light diffusers.
We then describe scattering parameters that are used to describe light propagation at textured samples. We present two measuring methods that are used to optically characterize samples: TIS (''Total Integrating Scattering'') measurements with spectrometer to determine reflectance, transmittance and haze, and ARS (''Angular Resolved Scattering'') measurements with a goniometric system to determine AID distributions and ADF functions.
The ARS system was upgraded with an integrating sphere and a larger photo-detector. We carried out calculations to determine reflectance, transmittance and haze from AID distributions, measured with ARS system, for a wavelength of the laser that was used as a light source. The system was tested on Asahi U type sample. We found out that ARS transmission measurements match well with TIS measurements. The differences can mainly be attributed to the non-isotropicity of the sample due to its final dimensions.
Larger errors occur with reflection measurements, therefore some improvements os the system are still required.
Slightly higher errors occur with transmittance measurements of ZnO:Al samples. These can be attributed primarily to smaller dimensions and damaged samples. With ARS system we can determine haze for transmission very well.
Larger errors occur in both ARS and TIS transmittance measurements of micro-textured UV plexiglas diffusers. Samples are not isotropic, resulting in ARS measurement error, and due to the thickness of the samples, an error occurs also in TIS measurements. The measurements of haze matched better. For isotropic and especially thicker samples, ARS measurements can better determine scattering parameters for transmission than TIS measurements.
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