Persistent photoconductance in a-Si: H/a-SiNx: H multilayers

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Abstract
A very large persistent photoconductivity (PPC) exceeding the dark conductivity of the annealed state by a factor of more than 105 has been observed in amorphous semiconductor multilayers consisting of alternating layers of hydrogenated amorphous silicon (a-Si: H) and hydrogenated amorphous silicon nitride (a-SiNx: H). The dependence of this PPC on exposure time, on light intensity and spectral content, on exposure temperature, and the thickness dn of the silicon nitride and the thickness ds the silicon layers and on doping in the silicon layers has been investigated. The PPC effect inereases with inereasing dn and decreases with inereasing ds. It is caused by light excitation in the silicon layers. A model is presented that explains the PPC in these multilayers in terms of hopping injection of carriers into the nitride layers. It is suggested that injected carriers produce metastable structural changes in the silicon nitride which anneal above an eauilibration temperature TE of about 460 K. One might conclude that the hydrogenated silicon alloys behave similarly to a-Si: H as hydrogen glasses with corresponding structural metastabilities.