{"id":{"repo_id":"mit","oai_identifier":"oai:dspace.mit.edu:1721.1/62528"},"canonical_url":"https://search.dev.ndltd.org/etd/mit/oai:dspace.mit.edu:1721.1/62528","repository":{"repo_id":"mit","name":"MIT","base_url":"https://dspace.mit.edu/oai/request"},"display":{"title":"Control of morphology for enhanced electronic transport in PECVD-grown a-Si : H Thin Films","abstract":"Solar cells have become an increasingly viable alternative to traditional, pollution causing power generation methods. Although crystalline silicon (c-Si) modules make up most of the market, thin films such as hydrogenated amorphous silicon (a-Si:H) are attractive for use in solar cell modules because of the capacity to fabricate cells with much less material. However, several challenges exist in making this material a more practical alternative to c-Si; despite having superior optical absorption properties, a-Si:H suffers in electronic transport, having a hole mobility 3-7 orders of magnitude less than that of c-Si. In the MOSFET transistor industry, carrier speeds and thus mobilities of c-Si were improved through the application of stress in the material. This work hypothesizes that a similar application of stress on a-Si:H thin films can enhance this material's hole mobility. A comprehensive study of the parameter space for a plasma enhanced chemical vapor deposition technique used to produce a-Si:H is performed. This enables the control of stress within the deposited film, from compressive to tensile; the mechanical limits of the material resulting in buckling and delamination failure are observed. Further characterization of a-Si:H thin films with different levels of engineered stress was performed; an analysis of the films' surface using AFM measurements to calculate a fractal dimension for each did not result in a significant descriptor of the surfaces' domain distribution. This work includes a detailed analysis of the theory of time-of-flight for measuring carrier mobility in thin film materials, and the system requirements needed to perform them.","abstract_html":"Solar cells have become an increasingly viable alternative to traditional, pollution causing power generation methods. Although crystalline silicon (c-Si) modules make up most of the market, thin films such as hydrogenated amorphous silicon (a-Si:H) are attractive for use in solar cell modules because of the capacity to fabricate cells with much less material. However, several challenges exist in making this material a more practical alternative to c-Si; despite having superior optical absorption properties, a-Si:H suffers in electronic transport, having a hole mobility 3-7 orders of magnitude less than that of c-Si. In the MOSFET transistor industry, carrier speeds and thus mobilities of c-Si were improved through the application of stress in the material. This work hypothesizes that a similar application of stress on a-Si:H thin films can enhance this material's hole mobility. A comprehensive study of the parameter space for a plasma enhanced chemical vapor deposition technique used to produce a-Si:H is performed. This enables the control of stress within the deposited film, from compressive to tensile; the mechanical limits of the material resulting in buckling and delamination failure are observed. Further characterization of a-Si:H thin films with different levels of engineered stress was performed; an analysis of the films' surface using AFM measurements to calculate a fractal dimension for each did not result in a significant descriptor of the surfaces' domain distribution. This work includes a detailed analysis of the theory of time-of-flight for measuring carrier mobility in thin film materials, and the system requirements needed to perform them.","abstract_has_math":false,"creators":["Castro Galnares, Sebastián"],"institution":"Massachusetts Institute of Technology","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":"Massachusetts Institute of Technology. Dept. of Mechanical Engineering.","school":null,"contributors":[],"advisors":["Tonio Buonassisi."],"committee_chairs":[],"committee_members":[],"year":2010,"date_issued":"2010","date_published":"2010","updated_at":"2026-07-22T22:21:34Z","subjects":["Mechanical Engineering."],"languages":["eng"],"rights":["M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. 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Although crystalline silicon (c-Si) modules make up most of the market, thin films such as hydrogenated amorphous silicon (a-Si:H) are attractive for use in solar cell modules because of the capacity to fabricate cells with much less material. However, several challenges exist in making this material a more practical alternative to c-Si; despite having superior optical absorption properties, a-Si:H suffers in electronic transport, having a hole mobility 3-7 orders of magnitude less than that of c-Si. In the MOSFET transistor industry, carrier speeds and thus mobilities of c-Si were improved through the application of stress in the material. This work hypothesizes that a similar application of stress on a-Si:H thin films can enhance this material's hole mobility. A comprehensive study of the parameter space for a plasma enhanced chemical vapor deposition technique used to produce a-Si:H is performed. This enables the control of stress within the deposited film, from compressive to tensile; the mechanical limits of the material resulting in buckling and delamination failure are observed. Further characterization of a-Si:H thin films with different levels of engineered stress was performed; an analysis of the films' surface using AFM measurements to calculate a fractal dimension for each did not result in a significant descriptor of the surfaces' domain distribution. 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However, several challenges exist in making this material a more practical alternative to c-Si; despite having superior optical absorption properties, a-Si:H suffers in electronic transport, having a hole mobility 3-7 orders of magnitude less than that of c-Si. In the MOSFET transistor industry, carrier speeds and thus mobilities of c-Si were improved through the application of stress in the material. This work hypothesizes that a similar application of stress on a-Si:H thin films can enhance this material's hole mobility. A comprehensive study of the parameter space for a plasma enhanced chemical vapor deposition technique used to produce a-Si:H is performed. This enables the control of stress within the deposited film, from compressive to tensile; the mechanical limits of the material resulting in buckling and delamination failure are observed. Further characterization of a-Si:H thin films with different levels of engineered stress was performed; an analysis of the films' surface using AFM measurements to calculate a fractal dimension for each did not result in a significant descriptor of the surfaces' domain distribution. This work includes a detailed analysis of the theory of time-of-flight for measuring carrier mobility in thin film materials, and the system requirements needed to perform them."],"dc:description.degree":["S.M."],"dc:identifier.uri":["http://hdl.handle.net/1721.1/62528"],"dc:language.iso":["eng"],"dc:publisher":["Massachusetts Institute of Technology"],"dc:rights":["M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. 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