(Dr. Zhuomin Zhang, advisor)

"Spectral Radiative Properties of Thin Films with Rough Surfaces Using Fourier-Transform Infrared Spectrometry"

Abstract

Thin films are used in many energy conversion applications, such as photodetectors and solar cells. Accurately predicting the radiative properties of thin films with rough surfaces is necessary but can be challenging due to the complexity arising from light scattering and interferences at the microscale. Previous studies showed that scalar scattering theory could yield reasonable agreement with certain experiments; however, their applicability to various surface conditions has not been established. This thesis describes measurements of the spectral transmittance and reflectance of several thin-film materials (including crystalline silicon wafers and a polycrystalline diamond film) in the mid-infrared spectral region (2 – 20 ?m), using a Fourier-transform infrared (FT-IR) spectrometer. The transmittance and reflectance were calculated using thin-film optics for the double-side polished samples and scalar scattering theory for the single-side polished samples. The effect of partial coherence was considered using a fringe smoothing technique. Good agreement between the predicted and measured radiative properties has been achieved for double-side polished silicon wafers and for the diamond film. The disagreement for some single-side polished silicon wafers may be inherently related to their surface microstructures, as suggested from surface topographic data and images obtained from surface profilometry and microscopy. Future research is proposed to investigate the correlation between the detailed surface characteristics and the conical-conical transmittance and reflectance.