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The temperature to which thin chalcogenide film is heated by a light pulse with a minimum power causing destruction is shown to exceed substantially the melting temperature of the material. Local destruction of films under the action of electric current or light may be characterized by a critical power Wc, i.e., a minimum power causing the destruction of a material. This parameter determines the limiting power level that amorphous films used in memory devices, waveguides, and switches can withstand. The mechanism of destruction is conventionally related to a temperature rise. No reliable methods exist for measuring directly the temperature Tc to which a film is heated by a short light pulse with power Wc. In this connection we evaluated Tc from the dependence of Wc on pulsed exposure duration and also by comparing Wc with the power levels which induce melting or crystallization, occurring in the temperature interval well-known for long exposures. We used as objects of study films of the chalcogenide glass Ge15As4Te81 of thickness L1 equals 0.15 - 0.3 micrometer, prepared by vacuum evaporation on glass substrates. Films of this and similar compositions show a reversible glass-crystal transition and find application in electrical or optical memory cells. The action of light on the substance was affected by an argon ion laser (lambda equals 0.514 micrometer). A modulating system furnished light pulses 0.2 microseconds to several seconds long. The laser beam was focused on the film to produce a spot with an area S less than or equal to 20 micrometers squared. The effect of exposure was monitored by measuring the transmission for a probing light beam (lambda equals 0.63 micrometer) focused on the place of incidence of the primary beam which induced changes in the optical properties of the film. Additionally, the film was viewed with a transmission microscope. Crystallization caused a decrease in transmission, whereas amorphization led to an increase in the transmission of a preliminarily crystallized film. When the critical value of power Wc was achieved, a local destruction in the form of a 'hole' was observed in the film.
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