Temperature dependent switching behavior and photovoltaic effect in n-n semiconductor heterojunction VO₂/Nb:TiO₂

The little-known n-n semiconductor heterojunctions are potential alternatives to p-n semiconductor junctions and metal/semiconductor Schottky junctions because they can show rectification if the interface between two n-type semiconductors with different electron affinities is sufficiently abrupt. Herein, we report a temperature dependent switching behavior up to ∼10³ times in n-n semiconductor heterojunctions fabricated using an epitaxial growth of n-type VO₂ on the n-type wide-bandgap semiconductor Nb:TiO₂. The n-n heterojunction VO₂/Nb:TiO₂, which shows excellent rectifying behavior with a high conductivity at a large forward bias, can be turned into a metal/semiconductor Schottky rectifier above the metal-insulator transition temperature, which results in significant tunability of rectification ratio. Finally, we clearly demonstrated the existence of a notable photovoltaic effect in n-n heterojunctions VO₂/Nb:TiO₂.