Effects of High Electric Fields on Tunneling-Assisted Optical Electron Transitions in a-Si

A theoretical model for the optical absorption of amorphous silicon (a-Si) at high electric field aimed for ease of use is developed. Optical absorption is proportional to the number of possible transitions from valence band to conduction band. When an electron is excited by a photon, the atom it was bound to is ionized and bends all the energy levels to form a Coulombic potential funnel. A high electric field tilts all the energy levels. The Coulombic funnel and the tilted conduction band form a potential barrier through which an electron can tunnel, giving rise to additional available density of conduction band states, thus increasing the optical absorption. The model was used to calculate the optical absorption at zero electric field, 100 kV/cm, and 1 MV/cm. Results show that, although optical absorption change is barely perceptible at electric fields up to 100 kV/cm, the change is much more pronounced at an electric field strength of 1 MV/cm.