Persistent Photoconductivity in Doping-Modulated Amorphous Semiconductors

We have synthesized amorphous-semiconductor superlattices consisting of alternating layers of $n$-type and $p$-type doped, hydrogenated, amorphous silicon. These new amorphous semiconductor structures exhibit a long-lived ($\tau \sim \mathrm{days}$) excess conductivity after a brief light exposure at room temperature. This effect may be attributed to spatial separation of the photocarriers by the $\mathrm{pn}$ junction fields or, alternatively, to defect centers having a barrier against retrapping of photoexcited carriers.