Merschjann, C.; Mews, M.; Mete, T.; Karkatzinou, A.; Rusu, M.; Korzun, B.V.; Schorr, S.; Schubert-Bischoff, P.; Seeger, S.; Schedel-Niedrig, Th.; Lux-Steiner, M.-Ch.: AgGaSe2 thin films grown by chemical close-spaced vapor transport for photovoltaic applications: structural, compositional and optical properties. Journal of Physics / Condensed Matter 24 (2012), p. 175801/1-10
Thin films of chalcopyrite AgGaSe2 have been successfully grown on glass and glass/molybdenum substrates using the technique of chemical close-spaced vapor transport. The high crystallinity of the samples is confirmed by grazing-incidence x-ray diffraction, scanning and transmission electron microscopy, and optical transmission/reflection spectroscopy. Here, two of the three expected direct optical bandgaps are found at 1.77(2) and 1:88.6/ eV at 300 K. The lowest bandgap energy at 4 K is estimated to be 1:82.3/ eV. Photoluminescence spectroscopy has further revealed the nature of the point defects within the AgGaSe2, showing evidence for the existence of very shallow acceptor levels of 5.1/ and 10.1/ meV, and thus suggesting the AgGaSe2 phase itself to exhibit a p-type conductivity. At the same time, electrical characterization by Hall, Seebeck and four-point-probe measurements indicate properties of a compensated semiconductor. The electrical properties of the investigated thin films are mainly influenced by the presence of Ag2Se and Ga2O3 nanometer-scaled surface layers, as well as by Ag2Se inclusions in the bulk and Ag clusters at the layers’ rear side.