Chapter 1: Introduction to Amorphous Semiconductors

Chalcogenide glasses are among the most widely known families of amorphous materials and have been studied extensively over the past few decades because of their interesting fundamental properties and wide commercial applications. They behave as semiconductors and exhibit a-semiconductor behaviour with band gap energy ranging from 1 to 3 eV. Thin film of chalcogenide glasses is known to be sensitive to the absorption of electromagnetic radiation and show a variety of photon induced effects as a result of radiation. On exposure to light or other radiations capable of exciting electron-hole pairs, chalcogenide glassy materials can exhibit structural changes. These structural changes are predominantly due to modifications in the atomic configuration, which consequently affect their physico-chemical properties such as the optical constants, energy bands and electronic transport phenomena of the semiconductor materials. Several photo-induced and laser-induced phenomena are observed in amorphous chalcogenide thin films. These changes are accompanied with the change in the optical constants, i.e., change in the optical band gap and optical absorption coefficient. Laser irradiation and light illumination can affect structural changes. Laser irradiation to chalcogenide glasses has been regarded as a process for spatially selected structural modification and/or modification in the localized density of states in the mobility gap of glassy materials. Laser induced changes in amorphous chalcogenide needs systematic investigation with a view to better understanding the mechanism of the phenomena taking place in them as well as their practical applications.