Interpretation of Recent On-State and Previous Negative Capacitance Data in Threshold Chalcogenide Amorphous Switch

Recent measurements studying the on-regime of the transient on-state characteristics (TONC) of an amorphous semiconductor Ovonic threshold switch, employing precisely balanced circuitry and isolated device voltage determination, have shown that the blocked on-state develops after an interruption subholding-voltage-time of about 100 ns. If the voltage interruption time below the holding voltage (Vh) is no greater than approximately 65–95 ns, the blocked on-state will not develop and the I-V curve will display a metal-like behavior. This is in agreement with a recombination single injection model for threshold switching in amorphous semiconductors because during the interrupt ion-time recombination takes place near the anode until a recombination front is established. In both the slow and fast relaxation regimes the general I-V curves thus derived are normally asymmetric about the origin, the former (slow) because of the structure of the interrogating wave form, the latter (fast) because of the lag in the response of current to voltage.The present paper gives a conceptual band structure model to interpret the new I-V data based on a shallow trapping band, using a recombinative single injection mechanism to describe threshold switching. This model is also invoked to explain the previously-measured negative capacitance in this material in terms of carrier separation characteristic of a relaxation semiconductor undergoing threshold switching and involving a recombination front.