Photodarkening in Amorphous As₂S₃ Thin Films

The photodarkening effect in amorphous As₂S₃ films is studied. The optical absorption edge shifts to lower energy after illumination at the bandgap light of 514.5 nm wavelength by an argon laser. The shift in well-annealed films can be recovered by annealing at 180°C for 1 h but in un-annealed films it is irreversible. In addition, it was found that the magnitude of photodarkening ΔE increased with the increase of illumination light intensity and illumination time. The reversibility of photodarkening in amorphous As₂S₃ films can be applied in optical memories.