A MIS device structure for detection of chemically induced charge carriers

Chemically induced electronic excitations were detected from adsorption of molecular ethylene and atomic oxygen on large-area Au/Al2O3/n-Si metal/insulator/semiconductor (MIS) diodes. The devices were fabricated with oxide thicknesses varying between 0 and 8 nm. For devices with an oxide layer less than similar to3 nm and relatively energetic surface adsorption reactions, electrons are excited by non-adiabatic energy transfer above the Fermi level and travel ballistically into the semiconductor. For low energy reactions and thicker oxides, charge transport in the device is dominated by ballistic hot holes created below the Fermi level which travel to the metal-insulator junction to electron donor states resulting in an effective forward-bias charging current. The energy-band structure of silicon as well as the density of interfacial states of the metal-insulator junctions strongly influences the electronic characteristics of the device. These MIS devices are suitable as molecular sensors for the detection of chemical species with low adsorption energies, such as hydrocarbons. (C) 2004 Elsevier B.V. All rights reserved.