Recent interest in composite materials based on hydrogenated amorphous silicon (a-Si:H) stems in part from its potential for technical applications in thin film transistors and solar cells. Previous reports have shown promising results for films of a-Si:H with embedded silicon nanocrystals, with the goal of combining the low cost, large area benefits of hydrogenated amorphous silicon with the superior electronic characteristics of crystalline material. These materials are fabricated in a dual-chamber plasma-enhanced chemical vapor deposition system in which the nanocrystals are produced separately from the amorphous film, providing the flexibility to independently tune the growth parameters of each phase; however, electronic transport through these and other similar materials is not well understood. This thesis reports the synthesis and characterization of thin films composed of germanium nanocrystals embedded in a-Si:H. The results presented here describe detailed measurements of the conductivity, photoconductivity and thermopower which reveal a transition from conduction through the a-Si:H for samples with few germanium nanocrystals, to conduction through the nanocrystal phase as the germanium crystal fraction XGe is increased. These films display reduced photosensitivity as XGe is increased, but an unexpected increase in the dark conductivity is found in samples with XGe > 5% after long light exposures. Detailed studies of the conductivity temperature dependence in these samples exposes a subtle but consistent deviation from the standard Arrhenius expression; the same departure is found in samples of pure a-Si:H; a theoretical model is presented which accurately describes the actual conductivity temperature dependence.
University of Minnesota Ph.D. dissertation. February 2015. Major: Physics. Advisor: Dr. James Kakalios. 1 computer file (PDF); xv, 109 pages, appendices A-B.
Bodurtha, Kent Edward.
Electronic transport in nanocrystalline germanium/hydrogenated amorphous silicon composite thin films.
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.