Shinji Yudate

Annealing-induced optical-bandgap widening of Cu2ZnSnS4 thin films with observation of simultaneous increase in local-structure ordering

We achieved annealing-induced optical-bandgap widening in Cu2ZnSnS4 (CZTS), which is a promising material for use in high-efficiency thin-film solar cells, and we performed synchrotron-radiation X-ray absorption fine structure (XAFS) measurements to study the reasons underlying the widening. CZTS thin-film samples were fabricated at a low temperature of 230 °C via sputtering with a CZTS ceramic target followed by annealing at up to 550 °C. Optical absorption spectroscopy revealed optical bandgap widening when the annealing temperature was ≥350 °C. Compositional changes, phase separations, and lattice strains were excluded as possible reasons. XAFS measurements revealed that the radial distribution functions (RDFs) around the Zn K-absorption edge almost completely corresponded to those of a kesterite structure. In addition, the RDFs indicated that the disorder of atomic positions within 1 nm from zinc atoms tended to decrease with increasing annealing temperature, which we conclude is the primary reason for the optical-bandgap widening.

Preparation of DLC films using microwave plasma CVD in open-air

Diamond-like carbon films (DLC) were deposited on both the Si(100) and stainless steel substrate by means of Microwave Plasma enhanced chemical vapor deposition (PECVD) under the open-air. From the XPS measurements, the sp2/(sp2+sp3) ratio of the DLC film is similar to that of the film grown by the conventional PECVD. In the pulse-modulated microwave PECVD growth at the duty ratio 30%, the impurity incorporation into the film reduced.