Understanding ovonic threshold switching of GeSe chalcogenide materials using electrical methodologies for extracting density of states

Abstract

As trap-related conduction is crucial in achieving ovonic threshold switching characteristics, identifying the distribution of traps in the chalcogenide matrix is essential. Herein, the density of states (DOS) near the valence band maximum level (EV) and conduction band minimum level (EC) of GeSe layers extracted using various electrical methodologies were analyzed. When electrons in the GeSe layer participate in activation under light injection, the DOS distribution at EV can be calculated. On the other hand, capacitance measurement with respect to frequencies allows the identification of the lowest energy levels of EC containing electrons that can respond to the provided AC signals. When an As dopant is introduced into the GeSe layer, the unified DOS distribution indicates a decrease in the Se element concentration owing to the over-coordinated Ge state. Therefore, increased DOS at EC is observed, which is in good agreement with the ab initio explanation. Additional simulations were performed considering plausible scenarios in which the variation in DOS profile depends on the parameters of the transport mechanism. These results reveal the ways in which threshold switching can be controlled and facilitate the understanding of electrically achieved behavior.