Abstract
Optical changes induced by band gap illumination were examined in amorphous red phosphorus films prepared by r.f. sputtering technique. The optical band gaps of as-sputtered films and the well-annealed films were evaluated to be 1.91 and 2.07 eV, respectively. Amorphous red phosphorus films were found to show two types of light-induced optical changes, i.e., reversible photodarkening and photodoping of noble metals, both of which are commonly observed in amorphous chalcogenide alloys; on illumination at ambient temperature, the optical band gap of the well-annealed films shifted by 0.04 eV to a lower energy, and this shift was restored by heating to a higher temperature above 200°C. The dissolution of Ag or Cu into the films was observed distinctly by light illumination. These were entirely analogous to those reported in amorphous chalcogenide alloys. A tentative model involving photodissociation was proposed for the photodarkening observed here.
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