{"592714":{"#nid":"592714","#data":{"type":"event","title":"Unexpected Electronic Transport Phenomena in Composite Amorphous\/nanocrystalline Thin Films","body":[{"value":"\u003Cdiv\u003E\r\n\u003Cdiv\u003E\r\n\u003Cdiv\u003E\r\n\u003Cdiv\u003E\r\n\u003Cdiv\u003E\r\n\u003Ch4\u003E\u003Cstrong\u003ESchool of Physics Hard Condensed Matter Seminar, Taylor Distinguished Professor, James Kakalios, University of Minnesota\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003EComposite materials consisting of nanocrystalline semiconductors embedded within a bulk amorphous semiconductor or an insulator have attracted interest for applications ranging from photovoltaics, thermoelectrics, thin film transistors, particle detectors and electroluminescent devices.\u0026nbsp;\u003C\/p\u003E\r\n\r\n\u003Cp\u003EThese materials combine the best of both worlds \u0026ndash; the thin film large area advantages of disordered semiconductors with the superior opto-electronic properties of crystals, and often display electronic properties not observed in either material separately.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EIn undoped nc-Si within hydrogenated amorphous silicon (a-Si:H) (a\/nc-Si:H), the dark conductivity increases with crystal fraction, with the largest enhancement of several orders of magnitude observed when the nanocrystalline density corresponds to a crystalline fraction of 2 \u0026ndash; 4%, but decreases for higher nanocrystal content.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EThe dark conductivity of n-type doped a\/nc-Si:H films displays three distinct conduction mechanisms: thermally activated conduction, multi-phonon hopping and Mott variable range hopping, as the crystal fraction and temperature of these films is varied.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EStudies of the thermopower of composite films of a-Si:H containing germanium nanocrystals find that transport changes from n-type to p-type as the nc-Ge concentration is increased, with a transition sharper than expected from a standard two-channel model for charge transport. Finally, the conductivity in the nc-Ge\/a-Si:H films is described by an anomalous hopping expression, ~ exp[(T\u003Csub\u003Eo\u003C\/sub\u003E\/T)\u003Csup\u003Ek\u003C\/sup\u003E] where k = \u0026frac34;, suggesting an entirely new conduction mechanism.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EThis research done in collaboration with Uwe Kortshagen, C. Blackwell, Y. Adjallah, L. Wienkes, K. Bodurtha, C. Anderson and J. Trask.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EThis work was partially supported by NSF grants NER-DMI-0403887, DMR-0705675, the NINN Characterization Facility, the Xcel Energy grant under RDF contract #RD3-25, NREL XEA-9-99012-01 and the University of Minnesota.\u003C\/p\u003E\r\n\u003C\/div\u003E\r\n\u003C\/div\u003E\r\n\u003C\/div\u003E\r\n\u003C\/div\u003E\r\n\u003C\/div\u003E\r\n","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":"","field_summary_sentence":[{"value":"Unexpected Electronic Transport Phenomena in Composite Amorphous\/nanocrystalline Thin Films"}],"uid":"27664","created_gmt":"2017-06-14 20:18:35","changed_gmt":"2017-06-14 20:20:48","author":"Alison Morain","boilerplate_text":"","field_publication":"","field_article_url":"","field_event_time":{"event_time_start":"2017-10-02T16:00:00-04:00","event_time_end":"2017-10-02T17:00:00-04:00","event_time_end_last":"2017-10-02T17:00:00-04:00","gmt_time_start":"2017-10-02 20:00:00","gmt_time_end":"2017-10-02 21:00:00","gmt_time_end_last":"2017-10-02 21:00:00","rrule":null,"timezone":"America\/New_York"},"extras":[],"groups":[{"id":"1278","name":"College of Sciences"},{"id":"126011","name":"School of Physics"}],"categories":[],"keywords":[{"id":"960","name":"physics"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[{"id":"1795","name":"Seminar\/Lecture\/Colloquium"}],"invited_audience":[{"id":"78761","name":"Faculty\/Staff"},{"id":"78771","name":"Public"},{"id":"174045","name":"Graduate students"}],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003Eamorain@gatech.edu\u003C\/p\u003E\r\n","format":"limited_html"}],"email":[],"slides":[],"orientation":[],"userdata":""}}}