INFLUENCE OF TEMPERATURE AND INTERELECTRODE DISTANCE ON THE NEGATIVE DIFFERENTIAL RESISTANCE IN METAL CHALCOGENIDE GLASSY SEMICONDUCTORS

An investigation has been carried out, to elucidate some aspects of the current-controlled negative differential resistance (CCNDR) effect in bulk metal-chalcogenide glassy semiconductors. Because this phenomenon has been shown to be mainly of a thermal nature, a model, from the thermodynamic point of view, was developed, including some aspects related to the thermistors theory. The main conclusion from this model is the appearance of a current filament, which showed up when the material switched from the high electrical resistance to the low electrical resistance state, forming a crystalline filament between both electrodes. The variation of the CCNDR parameters with temperature and interelectrodic distance was studied, using both coplanar point electrodes and coplanar disc electrodes. The experimental results show a good agreement with the expected behaviour from the proposed thermal model (especially when natural convection was considered as the heat-exchanging process between the material and the ambient surrounding). In addition an algorithm was found to simulate the phenomenon computationally, using the experimentally determined physical parameters for the samples under study.