Recently, however, the possibility to capitalize on this non-equilibrium effect has drawn active interest from the scientific community. As a result, the switching time of the device increases. This leads to the build-up of charge within the dielectric layer, increasing the switching threshold voltage. In fact, HCI is a main reason for transistor aging, with hot electrons or holes (depending on the doping of the transistor) tunneling into the gate dielectric.
In the past, hot carrier injection (HCI) was mainly regarded as an undesirable effect in device engineering. Those hot carriers are emitted from metals and semiconductors under experimental conditions. Surface femtochemistry, concerning the time resolved observation of reactions of adsorbates at various interfaces, oftentimes relies upon hot electron induced processes. In 1999 Zewail was awarded the Nobel Prize in Chemistry for his work on the disintegrations of iodocyanide ICN and sodium iodide NaI. Since molecular motion as well as chemical bond breaking and forming occurs on a femtosecond timescale, pump-probe experiments with femtosecond laser pulses allowed the first real time observation of the transition states of model chemical reactions. The term femtochemistry dates back to the pioneering work of Zewail, who employed femtosecond laser pulses in the investigation of molecular dynamics. Femtosecond laser pulse induced hot electron electrochemistry in aqueous solution allows a new perspective in the investigation of the electrode/electrolyte interface, the reactional pathways taken by short-lived intermediate species and laser processing in solution as a whole. Barring kinetic hindrance demanding the application of a certain overpotential, electrochemical reactions occur once the energy levels of the redox active species present in the electrolyte are crossed by the Fermi level of the electrode. This allows short-lived intermediates of electrode reactions to be studied. The thermoemission of nonequilibrium electrons was identified as a unique technique for the generation of picosecond current pulses which cannot be realized by conventional instrumentation.
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