Electron Field Emission from Semiconductors and Metals: Emission and Transport Time View of the Problem

Electron field emission from surfaces is of critical importance to basic plasma physics and development of advanced processing systems including for semiconductor manufacturing. Accurate accounting for electronic processes is a key when understanding plasma initiation and sustainable discharge and plasma-surface interaction.

It has been found (as early as in the 1960’s and documented to this day) that unlike in metals, where field emission obeys the Fowler-Nordheim (FN) law in a very large dynamic range, semiconductors (III-V and II-VI, diamond, carbon nanotubes) do not follow this law demonstrating unusual current-electric field relationships. At the same time, application of FN law remains a common tool in literature to describe emission from any kind of materials (be it metal or semiconductor).

This talk reviews some basic reasons why FN law should not be naturally expected to rule field emission from semiconductors. The problem is approached through analytically calculating time scales associated with quantum tunneling (emission barrier effect), two-dimensional space charge (vacuum effect) and charge transport (emitter material effect). Examples will be given of combinations of parameters (work function, field enhancement factor, tip geometry and doping) where semiconductor emission may appear as if it follows the FN law. Opposite examples will be given where the FN emission is vanished and taken over by the interplay between the space charge and material charge resupply effects. Comparisons between experimental results and the presented time-based analytical approach will be given.