On-state decay in NbO2: Relationship to recombination and to nonlinear I-V

Abstract

When addressed with a 1-MHz sinusoidal or triangular wave signal, the on-state of NbO2 shows two regimes of conductance. The lower-conductance regime occurs over the voltage range less than the holding voltage and shows, for the most part, superlinear I-V characteristics. Decay studies indicate that the time interval in this low-conductance or lower-current subregime is an inverse linear function of the on-state mobile charge density. This study also indicates that the subsequent positive peak current is also an inverse linear function of the time interval in the lower-conductance subregime of the previous cycle. The nonlinear lower-current subregime of the on-state I-V characteristics is thus directly related to the decay of the charge density of the true on-state, the decay being induced by a critical time duration of subholding voltage conditions. It is hence believed that the lower-current regime is a consequence of a relaxation-induced trapping phenomenon, and that the recovery of the high-conductance true on-state metal-like regime is due to the field-induced liberation of electrons from trapping centers. These data reinforce our earlier contention that both a critical charge concentration and a critical electric field intensity are inseparably necessary to maintain the on-state in NbO2.