Electron Field Emission from Semiconductors and Metals: Commonalities, Differences and RF Breakdown
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Abstract:
Electron field emission from surfaces is of critical importance to basic plasma and beam physics, cathode and injector R&D and their field applications. Field emission is also recognized as a key mechanism initiating RF breakdown in high power systems.
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 of applied electric fields, semiconductors 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 describe field emission from semiconductors. To support that, elementary picture of field emission from semiconductors and metals will be given through analytically calculating time scales associated with quantum tunneling (emission barrier effect), two-dimensional space charge (vacuum effect) and charge transport (emitter material effect). Further, more elaborate examples of silicon and cesium telluride will be given, where time-resolved electronic and thermal processes are captured under ultrahigh gradient C-band RF injector conditions and analyzed with regard to surface runaway scenarios leading to the vacuum breakdown and arc.