The dependence of the photo-induced excess conductivity in doping modulated amorphous silicon on exposure time, light intensity, and exposure temperature has been investigated. Our results can be explained by a novel defect center associated with boron. The growth of the excess conductivity is thermally activated and displays a power law dependence on light intensity and exposure time, where the exposure time power law exponent increases with light intensity.
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5. SUMMARY The photo-induced excess conductivity observed in doping modulated amorphous silicon is ascribed to charge storage at a novel defect, This defect is associated with the presence of boron and results in an excess electron density after illumination, either by trapping a photo-excited hole or by optical excitation of an electron from the center. Upon changing its charge state the defect undergoes a large structural reorientation which inhibits return to the pre-illuminated state, The creation of o E is thermally activated with an activation energy of 0,2 eV, The excess conductivity does not obey a reciprocity relation, but rather obeys a power law dependence on F and t e separately, where the exposure time power law exponent depends on the light intensity, 6, ACKNOWLEDGEMENTS This work was supported by Energy Conversion Devices Inc., and NSF DMR 8009225. One of us (J.K.) is an A.T.&T. Bell Labs Ph.D. Scholar. We are grateful to M. Hundhausen and L, Ley for a preprint of their work and for clarifying discussions with H, Ugur,