Optical Excitation of Semiconducting Field Emission Cathodes

Speaker: Dr. Stephen Purcell, Senior Researcher, Centre National de Recherche Scientifque (CNRS), France.
Date & Time: Fri, 2017-10-06 11:00 - 12:00
Location: Room 311
Local Contact: Dr. Alireza Nojeh
Intended Audience:

There has recently been extensive research on optically modulated and optically pulsed tip electron sources for new high field physics in the ultrafast laser community [1], electron microscopy [2] and ultrafast electron diffraction [3]. This is mostly the excitation of metallic tips or surfaces for which the quantum efficiency is extremely low eg. 10^-3-10^-4. This means that the high current emission will be limited by temperature effects. Another route is to exploit the photo-excitation of ptype semiconductor tips for which very high photon-electron conversion rates can be obtained (>10%), though at the expense of much slower time responses.

In contrast to the exponentially increasing current as a function of applied voltage common for metal emitters, semiconducting emitters can reveal strong current saturation related to a field-induced depletion zone originating at the emitter apex. The saturation current is highly sensitive to light and temperature. The basic behavior [4] and rough theory [5] was worked out many years ago followed by many experimental results with cursory analysis. However there is a dearth of in-depth measurements and concomitant understanding of the phenomenon in terms of semiconductor physics. Here we show that SiNWs can serve as an excellent platform for exploring FE from semiconductors with the added advantage for future applications that they are mass produced. Our principal present goal is to understand the time response and eventually apply this knowledge to higher current, faster, cone-like Si emitters. Some remarks on the potential of this work being extended to carbon emitters will be made.

The talk will start with a brief overview of our team’s activities in nanoscience.