Investigation of Metal-oxide-metal Structures for Optical Sensor Applications

In this work, we investigate metal-oxide-metal (MOM) structures for optical sensor applications in the case of low irradiances. MOM diodes can detect visible and infrared radiation in two different ways: using the rectifying properties of the diode (wave detection), or by thermal effects arising in the MOM junction upon irradiation. We present the fabrication, dc measurements, and visible and infrared measurements of MOM structures consist of ultrasmall (50 nm x 50 nm) symmetrical and asymmetrical tunnel junctions made by one electron beam lithography step and double-angle evaporation.

The detectors give strong responses for visible and near-infrared radiations, and the wavelength dependence of the responsivity can be altered using different detector geometries. According to our calculations none of the effects previously published in the literature (rectification, thermal effects) can explain the unusually high sensitivity of our sensors. The experimental results suggest that the operation of the sensors is related to generation-recombination of electron-hole pairs in the substrate.