Band Bending Engineering at Organic/Inorganic Interfaces Using Organic Self-Assembled Monolayers

Adsorbing strong electron donors or acceptors on semiconducting surfaces induces band bending, whose extent and magnitude are strongly dependent on the doping concentration of the semiconductor. This study applies hybrid density-functional theory calculations together with the recently developed charge reservoir electrostatic sheet technique to account for charge transfer from the bulk of the semiconductor to the interface. This study further investigates the impact of surface-functionalization with specifically tailored self-assembled monolayers (SAMs). For the example of three chemically-similar SAMs, that all bond to the ZnO surface via pyridine docking groups, it is shown that the SAMs introduce shallow or deep donor levels that pin the band bending at the position of the SAM's highest occupied molecular orbital. In this way, the magnitude of the induced band bending can be controlled by the type of SAM, to a point where the doping-concentration dependence is completely eliminated.