Metastable effects in hydrogenated amorphous silicon–silicon nitride multilayers

Abstract

The metastable effects arising from bias voltage, light illumination, and thermal quenching in hydrogenated amorphous silicon--silicon nitride (a-Si:H/a-${\mathrm{SiN}}_{\mathit{x}}$:H) multilayers have been studied. The coplanar conductance increases with bias voltage at moderately high voltages and decreases after bias stressing even at room temperature. After a brief light illumination, upon which the Staebler-Wronski defect is hardly created, we observed persistent photoconductivity (PPC) and an increase of sub-band-gap absorption in the multilayers. Annealing above the film deposition temperature decreases the PPC effect, but the increase of the sub-band-gap absorption for the PPC state is observed, indicating that the PPC effect is correlated with an increase of the gap state near the interfaces. We also observed an excess conductivity in the intentionally nitrogen-contaminated a-Si:H film by light illumination at an elevated temperature. Contrary to an unlayered intrinsic a-Si:H, the conductivity of a multilayered film increases upon thermal quenching. A possible model is proposed to explain the metastable effects in a-Si:H/a-${\mathrm{SiN}}_{\mathit{x}}$:H multilayers.