Transmission Electron Microscopy and Nanoprobe Analysis of Ferroelectric Thin Films

Thin-film ceramic materials have a variety of electronic applications. Several deposition techniques are currently being used to produce such films with specific properties. For example, rf-sputtered ferroelectric perovskite films, with total thicknesses less than 0.5 μ.m, are being integrated with semiconductor devices as elements for non-volatile memories. Since there is a definite need to characterize these thin films after deposition, electron microscopy has been utilized as one of the most powerful techniques available for examining their morphology and microstructure. Transmission electron microscopy (TEM) examination of these oxides proved difficult. New TEM sample preparation techniques had to be developed in order to avoid artifacts. Ion milling had to be kept to a minimum because many ferroelectric materials contain lead or other volatile elements. Even though milling has worked quite well under certain conditions, other techniques, such as microtoming, have been successfully used by the authors. In this work, both kinds of sample preparation are explored and compared. Particular emphasis is placed on the understanding of the compositional and microstructural variability of these films, as they are integrated in semiconductor devices

Scanning Capacitance Spectroscopy on n\u3csup\u3e+\u3c/sup\u3e-p Asymmetrical Junctions in Multicrystalline Si Solar Cells

We report on a scanning capacitance spectroscopy (SCS) study on the n+-p junction of multicrystalline silicon solar cells. We found that the spectra taken at space intervals of ∼10 nm exhibit characteristic features that depend strongly on the location relative to the junction. The capacitance-voltage spectra exhibit a local minimum capacitance value at the electrical junction, which allows the junction to be identified with ∼10-nm resolution. The spectra also show complicated transitions from the junction to the n-region with two local capacitance minima on the capacitance-voltage curves; similar spectra to that have not been previously reported in the literature. These distinctive spectra are due to uneven carrier-flow from both the n- and p-sides. Our results contribute significantly to the SCS study on asymmetrical junctions

Imaging Spatial Variations of Optical Bandgaps in Perovskite Solar Cells

A fast, nondestructive, camera-based method to capture optical bandgap images of perovskite solar cells (PSCs) with micrometer-scale spatial resolution is developed. This imaging technique utilizes well-defined and relatively symmetrical band-to-band luminescence spectra emitted from perovskite materials, whose spectral peak locations coincide with absorption thresholds and thus represent their optical bandgaps. The technique is employed to capture relative variations in optical bandgaps across various PSCs, and to resolve optical bandgap inhomogeneity within the same device due to material degradation and impurities. Degradation and impurities are found to both cause optical bandgap shifts inside the materials. The results are confirmed with micro-photoluminescence spectroscopy scans. The excellent agreement between the two techniques opens opportunities for this imaging concept to become a quantified, high spatial resolution, large-area characterization tool of PSCs. This development continues to strengthen the high value of luminescence imaging for the research and development of this photovoltaic technology.This work was supported by the Australian Renewable Energy Agency (ARENA) through Research Grant RND017 and the U.S. Department of Energy under Contract No. DE-AC36-08GO28308 with the National Renewable Energy Laboratory (NREL). The authors acknowledge the facilities and technical support from the Australian National Fabrication Facility (ANFF), ACT Node. H.T.N. acknowledges the fellowship support from the Australian Centre for Advanced Photovoltaics (ACAP)