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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Electrical Engineering and Computer Science

First Advisor

Venkateswara Bommisetty

Second Advisor

David Galipeau


The ability to deposit hydrogenated nanocrystalline silicon (nc-Si:H) on low-cost, flexible substrates over large areas makes it an attractive option for large scale production of solar cells. Nc-Si:H has also shown promise as a replacement for amorphous silicon in thin film transistors in large area LCD displays. The electronic properties of nc-Si:H depend greatly on its microstructure and therefore there is need to understand the phenomena and processes involved in charge transport. Recombination of electron-hole pairs can increase the defects in nc-Si:H which can lead to low efficiency in solar cells as well as instability in performance of thin film transistors. Hence studies of defect creation mechanisms and its effect at the nanoscale level could help in engineering more efficient and reliable devices.

Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared by RF sputtering and charges were injected into selective areas of the film at various bias voltages with an atomic force microscope (AFM). The changes in the topography and electrical conductivity of these regions were measured using contact-mode atomic force microscopy and current sensing AFM (CSAFM). Changes in average height and average conductivity were observed that were directly proportional to the magnitude of the bias

voltage at which charge was injected. The highest bias voltage (+10 V) caused the highest drop in local average current and increase in height. Charges were also injected at negative biases resulting in topography changes that were smaller than those caused by positive bias of the same magnitude. Decreases in local current were attributed to dangling bonds formed by the breaking of weak and strained silicon-silicon and siliconhydrogen bonds by the injected charges. It is speculated that the breaking of siliconhydrogen bonds released hydrogen atoms into microvoids where hydrogen molecules formed causing volumetric changes in the film. In conclusion, it was observed that RF sputtered nc-Si:H films had a large amount of weak and strained bonds which could be broken to create defects making it unstable for optoelectronic devices where the material is under a high bias.

Library of Congress Subject Headings

Atomic force microscopy
Solar cells
Nanostructured materials
Silicon crystals
Thin films
Charge transfer


Includes bibliographical references (pages 42-44)



Number of Pages



South Dakota State University


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