Correlation between Spectral Weight Redistribution and Band Gap Engineering in a‐Si: H Using XPS and Ellipsometry

Abstract This work presents a detailed analysis of localized electronic states and spectral weight transfer (SWT) in hydrogenated amorphous silicon (a‐Si: H) thin films. Using X‐ray Photoelectron Spectroscopy (XPS), Spectroscopic Ellipsometry (SE), Field Emission‐Scanning Electron Microscope (FE‐SEM) and Fourier Transform Infrared Spectroscopy (FTIR), we identify the presence of tail and defect states within the band gap and observe a systematic shift in spectral weight from low‐ to high‐energy transitions. These shifts correlate with changes in film microstructure and chemical bonding, as confirmed by XPS and SE measurements. The optical band gap and critical point energies vary with disorder, indicating band tailing effects. The findings highlight the significant role of disorder and hydrogenation in modulating the electronic structure of a‐Si: H, with implications for optimizing its performance in photovoltaic and optoelectronic applications. These results contribute to a deeper understanding of electronic localization phenomena and energy transfer mechanisms in amorphous semiconductors.