LASER INDUCED OSCILLATORY PHENOMENA IN a-GeSe₂ FILMS

Abstract
Studying the optical and photoelectric properties of 5 µ to 10 µ thick GeSe₂ amorphous films under the influence of focussed continuous He-Ne laser beams (just below band gap laser light of wavelength λ = 6328 Å) a region of medium intensity (1.4 to 2.7 kW/cm²) is found where low frequency (3 to 50 Hz) oscillations in the absorption coefficient and the photocurrent sets in. To date, this seems to be the only amorphous semiconductor in which a constant input evokes and oscillatory response, which is obviously a far from equilibrium phenomenon. The experimental optical data are compared with the microscopic model of cooperative charge disproportionation of defect centers described by P. Fazekas to explain the first cycle of oscillation which is a sudden switch from the transparent to the dark state. The simultaneous change in photocurrent is also discussed.