Date of Graduation

5-2011

Document Type

Thesis

Degree Name

Bachelor of Science in Electrical Engineering

Degree Level

Undergraduate

Department

Electrical Engineering

Advisor/Mentor

Manasreh, Omar

Abstract

New materials for thin film photovoltaic applications are being explored worldwide, and one of the most popular new implementations is the introduction of an intermediate band gap in the semiconductor energy structure. Careful manipulation of semiconductor lattice material can form nanostructures such as quantum dots, which can be tuned to control specific intermediate energy levels. The introduction of an intermediate band in photovoltaic devices has a theoretical potential sunlight-toelectricity efficiency of roughly 63%. However, a specific material challenge of these thin film devices is limited absorption of long wavelengths of light. To increase absorption of the sun's visible spectrum, plasmonic nanostructures may also be incorporated into the semiconductor structure. By scattering light horizontally and by matching incident wavevectors with waveguide modes within the absorbing layer, these plasmonic nanostructures can enhance the thin film absorption and increase device efficiency. To study this effect, a colloidal solution of gold nanoparticles was applied to the surface of a GaAs substrate with InAs quantum dots grown by Molecular Beam Epitaxy. Measurements of photoluminescence were performed on the semiconductor sample before and after nanoparticle deposition using various power settings for the excitation laser. Plasmonic enhancement due to light scattering is observed, and the enhancement factor is found to be inversely proportional to the excitation laser power. This supports the theory of light trapping in thin films due to plasmonic mechanisms. It also provides insight into the relationship between incident light intensity and potential absorption enhancement in thin-film semiconductors.

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