Growth characterization and optical modeling of hydrogenated silicon thin film solar cells based on spectroscopic ellipsometry

Spectroscopic ellipsometry (SE) is one of the most important optical characterization techniques available for accurately and precisely measuring structural parameters such as thicknesses, and optical properties such as index of refraction and extinction coefficient, for thin film materials. Its importance derives from the fact that it can provide a better understanding of useful physical and optical characteristics of thin films, as well as key inputs for optical modeling in order to better understand and predict the performance of complex multilayer devices.; In this thesis, several studies are described in which SE measurements are applied to characterize different materials used in the development of hydrogenated silicon (Si:H) solar cells. Ex situ SE was applied to characterize microstructurally textured thin films of tin oxide, a transparent conductor used in Si:H solar cells. Moreover, a rigorous physics-based optical model was developed in order to understand and predict the effects of tin oxide thin film optical properties and microstructure on the performance of solar cell devices.; Spectroscopic ellipsometry (RTSE), performed both in situ and in real time, was applied to deduce the microstructural evolution and phase diagrams of intrinsic Si:H deposited using different plasma excitation frequencies (rf: radio frequency and vhf: very high frequency); p-doped Si:H for n-i-p solar cell structures; and hydrogenated silicon germanium (Si 1-xGex:H). These thin film depositions were performed under several different conditions involving variations in hydrogen dilution ratio (which forms the abscissa of the phase diagram), plasma power, gas pressure, and substrate temperature. The phase diagrams depict the bulk thicknesses at which structural and phase transitions occur as a function of the hydrogen dilution ratio. Among these include the amorphous-to-amorphous phase transition [a → a], the amorphous-to-mixed phase transition [a → (a + muc)], and the mixed-to-single-microcrystalline-phase transition [(a + muc) → muc]. Furthermore, correlations between device performance and growth kinetics were used to establish general optimization criteria for photovoltaic applications of the films examined in this study.