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dc.contributor.advisorGu, Yi
dc.creatorWang, Qiaoming
dc.date.accessioned2017-06-19T16:20:12Z
dc.date.available2017-06-19T16:20:12Z
dc.date.issued2016
dc.identifier.urihttp://hdl.handle.net/2376/12007
dc.descriptionThesis (Ph.D.), Physics, Washington State Universityen_US
dc.description.abstractElectrical and optoelectronic properties of bulk semiconductor materials have been extensively explored in last century. However, when reduced to one-dimensional and two-dimensional, many semiconductors start to show unique electrical and optoelectronic behaviors. In this dissertation, electrical and optoelectronic properties of one-dimensional (nanowires) and two-dimensional semiconductor materials are investigated by various techniques, including scanning photocurrent microscopy, scanning Kelvin probe microscopy, Raman spectroscopy, photoluminescence, and finite-element simulations. In our work, gate-tunable photocurrent in ZnO nanowires has been observed under optical excitation in the visible regime, which originates from the nanowire/substrate interface states. This gate tunability in the visible regime can be used to enhance the photon absorption efficiency, and suppress the undesirable visible-light photodetection in ZnO-based solar cells. The power conversion efficiency of CuInSe2/CdS core-shell nanowire solar cells has been investigated. The highest power conversion efficiency per unit area/volume is achieved with core diameter of 50 nm and the thinnest shell thickness. The existence of the optimal geometrical parameters is due to a combined effect of optical resonances and carrier transport/dynamics. Significant current crowding in two-dimensional black phosphorus field-effect transistors has been found, which has been significantly underestimated by the commonly used transmission-line model. This current crowding can lead to Joule heating close to the contacts. New van der Waals metal-semiconductor junctions have been mechanically constructed and systematically studied. The photocurrent on junction area has been demonstrated to originate from the photothermal effect rather than the photovoltaic effect. Our findings suggest that a reasonable control of interface/surface state properties can enable new and beneficial functionalities in nanostructures. We also provide a practical guide for rational design of low-cost and high-efficiency nanowire solar cells, and the necessity of considering both optical and electrical effects. Particularly, the significant current crowding effect needs to be considered in on-going 2D nanostructure device development and optimization efforts. More importantly, our van der Waals metal-semiconductor junction devices provide a new route for junction constructions and could have great potential in optoelectronic device applications.en_US
dc.description.sponsorshipWashington State University, Physicsen_US
dc.language.isoEnglish
dc.rightsIn copyright
dc.rightsPublicly accessible
dc.rightsopenAccess
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/
dc.rights.urihttp://www.ndltd.org/standards/metadata
dc.rights.urihttp://purl.org/eprint/accessRights/OpenAccess
dc.subjectPhysicsen_US
dc.subjectMaterials Scienceen_US
dc.subjectNanotechnologyen_US
dc.subjectDevicesen_US
dc.subjectNanoscienceen_US
dc.subjectNanotechnologyen_US
dc.subjectScanning-Probe-Microscopyen_US
dc.subjectSemiconductorsen_US
dc.subjectTwo-Dimensional Materialsen_US
dc.titleElectrical and Optoelectronic Properties of Two-Dimensional Materials
dc.typeElectronic Thesis or Dissertation


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