Abstract

Bulk chalcogenide glass semiconductors have been shown to exhibit a large, yet fast absorption nonlinearity.¹ The greatly broadened absorption edge characteristic of these amorphous semiconductors offer the possibility for large dynamic optical nonlinearities over a much larger range of wavelengths than found in crystalline materials. In addition, amorphous semiconductors are attractive for optical device applications because they can be deposited easily on a variety of substrates. Thin films of amorphous arsenic sulfide, a chalcogenide glass semiconductor, have been deposited on quartz and silicon substrates by ion beam sputtering. This method of deposition produces films which are amorphous, smooth, and of excellent optical quality. Preliminary measurements using a cw pump-probe technique show that, unlike in crystalline materials, where bandfilling effects cause a decrease in absorption, the absorption increases with pump intensity over a broad range of probe wavelengths. As in the bulk,¹ the mechanism responsible for this effect is believed to be a result of structural disorder. Intraband transitions of a type forbidden in crystalline materials cause an increase in absorption at low energies when conduction band tail states are filled by bandgap energy radiation. Quantitative measurements of the change in the absorption spectrum of these films as a function of pump intensity and pump wavelength are presented.

© 1989 Optical Society of America