Exciton transport in SiO₂ as a possible cause of surface-state generation in MOS structures

Positive charge and surface states are found to accumulate at the Si-SiO2 interface in MOS structures which are illuminated by vacuum ultraviolet photons (≳9 eV) with a negative bias applied to the metal electrode. A series of experiments seems to rule out the obvious explanations for this effect - photon and hot-electron processes. We suggest the possibility that excitons, generated by photon absorption in the SiO2, diffuse to the Si-SiO2 interface where they are separated into a free electron absorbed into the silicon substrate and a hole trapped at the interface.