Conduction in non-crystalline systems

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Abstract
The on-state in a chalcogenide threshold switch is discussed on the basis of the double-injection model. The electron-hole gas in a conducting channel is compared with that in ‘droplets’ in illuminated germanium. It is shown that a mechanism for maintaining barriers at the electrodes proposed by Lee (1972) leads to a constant value of the current per unit area across the interface, so that total current is proportional to the cross sectional area of the conducting channel, in agreement with experimental results of Henisch and Pryor (1971). The minimum holding current occurs when the diameter of this area at the interface becomes less than the thickness of the chalcogenide film; the cross sectional area of the channel within the film is then greater than at the interface, so that the current density drops within the film and the transit time increases; recombination becomes important, setting up a space-charge. This has the effect of increasing the holding voltage, with the result that the device reverts to the off-state.