A light-induced increase in the dark conductivity is observed in composite thin films consisting of hydrogenated amorphous silicon (a-Si:H) containing nanocrystalline germanium (nc-Ge) inclusions, synthesized by co-deposition in a dual-chamber plasma enhanced chemical vapor deposition system. Unlike the Staebler-Wronski effect or persistent photoconductivity observed in amorphous semiconductors, this photo-induced excess conductivity is observed even in composite nc-Ge/a-Si:H films with a minimal photosensitivity. The decay of the excess conductivity follows a single-exponential time dependence, with a temperature independent time constant. We propose that spatial separation of photo-excited charge carriers by the compositional morphology present in the film, with tunneling of photo-excited holes into the germanium nanocrystalline inclusions, is involved in the creation and removal of this effect.
Bibliographical noteFunding Information:
This work was partially supported by NSF Grant No. DMR-0705675 and 1608937, the NINN Characterization Facility, the Nanofabrication Center, an Xcel Energy Grant under RDF Contract No. RD3-25, NREL Sub-Contract No. XEA-9-99012-01, and the University of Minnesota.
© 2018 Author(s).