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

摘要

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.