Material science aspects of phase change optical recording

Abstract

Chalcogenide thin films are used as the recording medium for phase change-type optical memory discs. The films are switched between amorphous and crystalline states using the heat of a focussed laser beam. Large reflectivity differences between amorphous and crystalline states are then used to store and retrieve the information. An active chalcogenide layer for this purpose should have a high optical absorption coefficient (α), and good structural and thermal stability. It should be possible to switch the chalcogenide layer between amorphous and crystalline states repeatedly within a short duration, the optical contrast should be high, and the material must have large cycling capability. Keeping the above requirements in mind, we have carried out systematic investigation of structural, optical and crystallization behaviour of thin films of various compositions of GaGeTe, Sb₂Te₃ and BiSe. These studies have shown that these materials can be good candidates for use as recording media in erasable phase-change optical recording.