The structure of a ZnSnAs2 thin film epitaxially grown on an InP substrate was evaluated using x-ray fluorescence holography. The reconstructed three-dimensional atomic images clearly show that the crystal structure of the ZnSnAs2 thin film is mainly of the sphalerite type, in contrast to the bulk form. A large disordering of the As layers is observed, whereas the positions of the Zn/Sn atoms are relatively stable. The analysis of the data indicates that the As layers serve as a buffer and relax the strain caused by the random occupation of Zn and Sn atoms. These results provide further understanding and a means of controlling the growth of Mn-doped ZnSnAs2, a high-Tc diluted magnetic semiconductor.
Lead phthalocyanine (PbPc) is well known to be used as a good near-infrared (NIR) light absorber for organic solar cells (OSCs) and photodetectors. The monoclinic and triclinic phases have been understood to absorb the visible and NIR regions, respectively, so far. In the present study, we demonstrated from the absorption spectra and theoretical analysis that the visible band considerably originates from not only the monoclinic but also the amorphous and triclinic phases, and revealed the exciton dynamics in the PbPc film from static/time-resolved photoluminescence (PL), which are first reported. By comparing the external quantum efficiency between PbPc- and ZnPc-based OSCs in relation to their structure, morphology, and optical (absorption and PL) characteristics, we unraveled the reasons behind the PbPc film used as a good absorber for NIR-sensitive devices.
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