Control of morphology for enhanced electronic transport in PECVD-grown a-Si : H Thin Films

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.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Castro Galnares, Sebastián

Advisor dc:contributor.advisor

• Tonio Buonassisi.

• Mechanical Engineering.

Statement 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. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/62528

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/62528