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Ellipsometry is a useful tool for studying the optical properties of thin films such as photovoltaic devices. We employ Müller matrix ellipsometry to study the thin film photovoltaic material copper indium gallium selenide Cu(In,Ga) Se2 (CIGS), a commercially relevant material with high energy conversion efficiency. Confocal microscopy reveals an rms roughness of 68 nm, which greatly affects the ellipsometry data. Rayleigh-Rice theory is employed to account for the optical properties of the surface roughness in the ellipsometry experiment, and a library search method is used to compare Müller parameters calculated for various CIGS compositions, to the measured data. The Müller parameters calculated with the Rayleigh-Rice model are found to correspond well with the measured data, and a surface roughness of 37nm and a correlation length of 125nm are extracted.
Maintaining a consistent product quality is critical for the thin film industry. Therefore, the development of highly accurate protocols able to detect variations and nonidealities in manufactured thin film devices is essential and helps improve production quality and decrease manufacturing costs. The present work will discuss the accuracy and reproducibility in the determination of the thickness of thin films relevant for optoelectronic industry using spectroscopic ellipsometry, starting with the importance of set-up calibration, the need for very well defined calibration standards suitable for real devices and not least, the importance of accurate data analysis. As ellipsometry is an indirect method and theoretical modelling is needed to obtain the desired information regarding the investigated samples (e.g. thickness, roughness, optical constants), the model uncertainty has to be discussed and taken into account. If for ideal samples consisting of single layers with well-known optical constants the determination of thickness and roughness is straight forward and pretty accurate, for real samples, more complex theoretical models are needed and extracting accurate information regarding the samples can be very challenging. With careful calibration and a multidisciplinary approach, a combined measurement methodology can be developed enabling reliability, comparability, and accuracy. For production-relevant operation, maintaining the ease of use and scalability of ellipsometry as a technique can also be retained.
In the search for highly efficient, low-cost, non-toxic, transparent conductive oxides (TCOs) suitable for large area applications for photovoltaics, ZnO and ZnO-related materials have received considerable attention. In the present work, Al and Ga doped ZnO films on oxidized Si substrates are characterized using mainly variable angle spectroscopic ellipsometry; additional optical and non-optical techniques were employed to confirm and support the ellipsometric models considered. The samples were obtained by means of pulsed chemical vacuum deposition (CVD) and atomic layer deposition (ALD).
As known from previous studies the presence of dopants in ZnO thin films generally induce significant changes in the optical, electrical and morphological properties. We present our findings for a series of Al and Ga doped ZnO layers with different concentrations of the dopants, discussing their influence on the optical and electrical properties.
The present study investigates the use of imaging and mapping ellipsometry to determine the properties of non-ideal and patterned thin film samples. Samples which are candidates for future references and standards were prepared for this purpose. The samples investigated were lithographically patterned SiO2 and photoresist layers. The thickness and the optical constants of the two materials were determined using spectroscopic ellipsometry in the visible spectral range. On a larger lateral scale of several mm lateral resolution, the homogeneity was investigated using a goniospectral rotating compensator ellipsometer. A nulling imaging ellipsometer was used to determine the properties of the sample on a smaller scale of 25–150 µm.