NEA Silicon

Activation of Si to NEA is also much more critical than activation of the III-V compounds. The procedure is similar to that used for the III-Vs, but unlike the amorphous and arbitrarily thick layers found there, the Si/(CsO) layer must be perfect in both structure and composition. For NEA Si, a single layer of Cs must reside on top of plateaus of four Si atoms, with oxygen, even though applied last, residing within caves below four Si atoms, forming an oxygen sublattice beneath the Si/Cs structure [5.30, 31]. As little as 0.1 % surface contamination can destroy Si NEA, and the (100) face is the only one capable of NEA activation [5.72]. 

In NEA Si cold cathode devices, a planar diode is biased to inject electrons from an n-type substrate to a p-type NEA surface layer, where current is drawn off by an electric field. (Other cold cathodes of different design have been demonstrated in III-V structures [5.130-132].) This efficient emission could be useful in replacing hot (thermionic) cathodes in IR sensitive devices where a low luminence source with small electron energy spread is desirable, but requirements of zero contamination along with electron emission-density restrictions and long-term instability problems have so far prevented practical use. 

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