MODELING AND REALIZATION OF AN AMORPHOUS-SILICON DEVICE WITH NEGATIVEDIFFERENTIAL RESISTANCE

We present modeling and realization of a two terminal hydrogenated amo rphous silicon device with bistable current-voltage (I-V) characterist ics, potentially suitable to obtain a new generation of switch and mem ory in large area application, The structure is basically constituted by three stacked junctions: p(+)-i-n(-), n(-)-i-p(-), p(-)-i-n(+)., A numerical device model allows to investigate in detail the device beha vior pointing out the fundamental role of the two lightly-doped n(-) a nd p(-) layers. In the OFF condition the central junction is reverse b iased and limits the current in the device. The transition OFF-ON star ts when, increasing the applied voltage, one of the two lightly-doped layers becomes completely depleted. In the ON state high injection of both carriers from the external-doped layers completely hides the dopi ng concentrations of the bases and the device behaves like a single fo rward biased p(+)-i-n(+) structure. The transition ON-OFF occurs when, decreasing the applied voltage, the free carrier densities in the lig htly-doped layers become lower than the dopant concentrations, This tr ansition is thus mainly dependent on the recombination processes occur ring in the central-doped layers, Devices with hysteresis around 2 V a nd turn-on voltages ranging from 12 to 15 V have been obtained.