Chemically induced charge carrier production and transport in Pd/SiO2/n-Si(111) metal-oxide-semiconductor Schottky diodes

摘要

The energy transfer associated with reactions at metal surfaces produces energetic electrons and holes. Using ultrathin films of Pd on metal-semiconductor (MS) and metal-oxide-semiconductor (MOS) diode structures, we have investigated reaction-induced electrical phenomena associated with a variety of molecular and atomic interactions with the Pd surfaces. Distinct electronic signals are observable for species as diverse as atomic oxygen, xenon, and molecular hydrocarbons. Both MS and MOS devices allowed the detection of the chemically induced excitation of electron-hole pairs for highly exothermic chemisorption. Electronic signals from gas species with low adsorption energies were only observed in MOS devices with a thin oxide layer between the active metal film and the semiconductor. The density and distribution of interfacial states in the MOS devices have been found to be an important factor in understanding the origin and transport pathways of these "chemicurrents." A dynamic model is introduced to explain the displacement currents in the MOS devices during low-energy gas-surface interactions.