Optical response of metal–insulator–metal heterostructures and their application for the detection of chemicurrents

Abstract

The optical response of thin-film metal–insulator–metal (MIM) systems of tantalum–tantalum oxide–Au type is studied by recording the macroscopic current across the device resulting from the low-energy electron–hole pairs excited in the metals by red and near-infrared (NIR) light (hν<2 eV). It is observed that current flows from the top Au to the back Ta electrode, although a larger number of photons is absorbed in the latter. This directional preference is attributed to the built-in electric field across the oxide layer. The yield per photon increases strongly as photon energy becomes comparable to the barrier height. Current exhibits a strong dependence on bias voltages applied across the oxide layer. Photoyields induced by NIR light (hν∼1.5 eV) were found to be comparable to recently observed chemicurrents arising from exposure of a MIM sensor to atomic hydrogen, when compared on a current per photon to current per impinging hydrogen atom basis.