Real-time Stokes vector spectroscopy and its application to the characterization of inhomogeneous thin films

Real Time four-parameter Stokes Vector Spectroscopy has been developed and applied to obtain structural parameters and optical properties of thin films with different degrees of inhomogeneities. With this instrument it is possible to simultaneously obtain spectra of the four elements of the Stokes vector, namely the ellipsometry angles (Psi, Delta), the degree of polarization p, and the polarized reflectance R, at a minimum acquisition time of 32 ms, with 100 spectral points in the 1.5--4.5 eV range.; As a first application of this instrument, it is measured the resonant circular dichroism and circular birefringence presented by helicoidal thin films. This was the first observation of these properties in such materials. As a second application, we demonstrate the capabilities of Real Time Stokes Vector Spectroscopy to obtain the thickness gradient evolution of a diamond thin film deposited by micro-wave Plasma Enhanced Chemical Vapor Deposition (muw-PECVD). This thickness gradient evolution is determined by modeling the degree of polarization spectra using an incoherent sum of different polarizations states. As a result, the thickness gradient presents a linear increase as a function of bulk film thickness, due to the lateral inhomogeneity of the microwave plasma. As a third application, we demonstrate how to obtain useful information from the polarized reflectance R. The technique has been applied to characterize the preparation and processing of hydrogenated amorphous silicon (a-Si:H)-based materials and solar cell structures, deposited on macroscopically rough transparent conductor oxides. The study consists on a preliminary characterization of the optical properties, macroscopic and microscopic structures of textured (i.e., macroscopically rough) Asahi-U SnO2, which are commonly used in photovoltaics industry. Next, a p-i-n structure is fabricated on the glass/SnO2 superstrate. Post-deposition data analysis of the ellipsometry angles (Psi, Delta) and the polarized reflectance yields the evolution of the bulk, surface microscopic roughness, interface layers and macroscopic roughness of the p- and i- layers, and also the optical properties in the measured spectral range. The structural results obtained by Spectroscopic Polarimetry are confirmed by a study of Atomic Force Microscopy and edge-on Scanning Electron Microscopy. Finally, Real Time Stokes Vector Spectroscopy (RTSVS) is applied to the study of the nucleation of p-doped hydrogenated microcrystalline Silicon (muc-Si:H) deposited by rf-PECVD on specular ZnO under different hydrogen dilutions, in order to identify the ideal hydrogen dilution to obtain immediate nucleation of muc-Si:H, and minimum etching by excessive dilution. This study is used as a mapping road to the fabrication of p-i-n solar cells consisting on muc-Si:H:B p-layer, a-Si:H i layer, a-Si:H:P layer, on textured SnO2/glass and textured ZnO/SnO 2/glass superstrates. A comparative study is made among the optical properties and structural characteristics of the p-layers deposited on both textured and specular substrates.