PHOTOCURRENT IN THE SUB BANDGAP REGION OF A-SI:H PHOTOSENSITVE DEVICES INDUCED BY AG NANOPARTICLES

摘要

In this contribution the absorption by defect states in hydrogenated amorphous silicon (a-Si:H) photosensitive devices in the environment of resonant absorbing silver nanoparticles (Ag NPs) is investigated. The location of defects in the strong electromagnetic fields accompanied by the localized surface plasmon (LSP) resonance of the Ag NPs enable high transition rates between the defect states and the conduction band. This results in a significant signal for near infrared (NIR) photon energies in external quantum efficiency (EQE) measurements. Dominant transitions take place for defect levels with an energetic distance from the conduction band, equal to the LSP resonance energy. Introducing a boron doped layer in direct contact to the NPs leads to a decrease of the NIR EQE signal. This gives evidence for the existence of the NP induced defect states in the a-Si:H material. The p-type doping shifts the Fermi level towards or below the defect states resulting in their depletion. Therefore these states cannot contribute to sub bandgap photon absorption resulting in a decreased NIR EQE signal.