Dangling Bond Defects on Si Surfaces and Their Consequences on Energy Band Diagrams: From a Photoelectrochemical Perspective

Using silicon in multijunction photocells leads to promising device structures for direct photoelectrochemical water splitting. In this regard, photoelectron spectra of silicon surfaces are used to investigate the energetic condition of contact formation. It is shown that the Fermi‐level position at the surface differs from the values expected from their bulk doping concentrations, indicating significant surface band bending which may limit the overall device efficiency. In this study, the influence of different surface preparation procedures for p‐ and n‐doped Si wafers on surface band bending is investigated. With the help of photoemission and X‐ray absorption spectroscopy, Si dangling bonds are identified as dominating defect centers at Si surfaces. These defects lead to an occupied defect band in the lower half and an unoccupied defect band in the upper half of the Si bandgap. However, partial oxidation of the defect centers causes a shift of defect bands, with only donor states remaining in the Si bandgap. Source‐induced photovoltages at cryogenic temperatures indicate that partial surface oxidation also decreases the recombination activity of these defect centers. It is shown that defect distribution, defect concentration, and source‐induced photovoltages need to be considered when analyzing Fermi‐level pinning at Si surfaces.