Observation of two-level defect system in amorphous Se superlattices

Amorphous Se is a well-known photoconductor from its early applications in xerography and ultra-sensitive photodetectors like the High-gain Avalanche Rushing Photoconductor (HARP) device. The established way of fabricating the photoconductor for the HARP is rotational thermal evaporation using multilayers of Se and As2Se3. However, the electronic effects of multilayering have not yet been clarified. In this report, we investigated the multilayer structure as a superlattice of Se and As2Se3 fabricated using rotational evaporation and show that the superlattice structure results in the uniformization of the defect levels in the base materials. We found four energy levels associated with defects in As2Se3 and three levels in amorphous Se. In comparison, the superlattice structure of the two materials shows two clear energy levels at E-C,E-Se - 0.533 eV and E-V,E-Se+0.269 eV. The resulting two occupied energy levels explain the photoelectronic and transport properties observed in multilayer amorphous Se. This result reinvents the multilayer structure as a material with observed quantum effects, which significantly improves the material performance in photodetection. Published under license by AIP Publishing.