Electroabsorption Modeling in Hydrogenated Amorphous Silicon

Measurements of electroabsorption in intrinsic hydrogenated amorphous silicon at electric fields up to 190 kV/cm in the photon energy range between 1.45 and 2.15 eV are performed, using two different methods-by measuring transmission with and without an applied dc electric field and with the use of a lock-in amplifier. A numerical model of the electroabsorption is developed, which is based on the assumption that there is no angular dependence of electron emission attempts on the electric field. Instead, the density of states (DOS) in the neighborhood of the initial site is shifted toward slightly higher or lower energies by the electric field, depending on the direction of the electron emission from the initial site relative to the electric field. The shifted DOS affects the success rate of emission attempts. We interpret the effect of the electric field as an effective DOS, which in turn affects the optical absorption. The developed model is in good qualitative and quantitative agreement with the measurements of optical absorption change in the measured range of photon energies.