Time-dependent transport in amorphous semiconductors: instability in the field-controlled regime

A time-dependent trap-limited conduction scheme is used to analyze the transient behavior of bistable homogeneous amorphous semiconductors when either the electric field or the current density is prescribed. Numerical outcomes confirm that, for a current-controlled system, the working point is unique and stable in any region of the current-voltage characteristic, while in a field-controlled system the negative differential-resistance region is unstable even in absence of circuit parasitics. The proposed theoretical approach represents a valid tool to grasp the relevant time-dependent features of the Ovonic switching in chalcogenide materials.