Dynamics and bonding of bond-centered hydrogen in amorphous hydrogenated Si: vibrational and optical signatures

It is well accepted that the so called bond-centered hydrogen (BCH) is an important and frequently occurring structural complex for both amorphous and crystalline semiconductors. BCH defects play a significant role in crystalline silicon and especially in amorphous hydrogenated silicon (a-Si:H) due to its application in photovoltaics and microelectronics. Vibrational and optical spectra of amorphous hydrogenated silicon (a-Si:H) contain essential information about the microscopic properties of the hydrogen atoms, including stability of the hydrogen bond responsible for a-Si:H quality for photovoltaic application. To decode this information from the experimental spectra, we developed a computational approach to comprehensively track hydrogen behaviour in both ordered (crystalline) and disordered (non-crystalline) materials, and applied it to a-Si:H. Our focus is on different hydrogen complexes, responsible for stability of the a-Si:H material and its degradation. Since the bond-centered hydrogen is a typical complex in both crystalline silicon (c-Si) and amorphous silicon, we present a parameter free comparative vibrational and optical simulation of BCH in c-Si and a-Si:H. Vibrational spectra, electron density of states (DOS) and optical response were calculated for BCH and related systems. We have identified vibrational signatures of hydrogen instability in the amorphous Si network and c-Si. Bond-centered-hydrogen complexes observed have been characterized vibrationally and optically.