Field Emission from Semiconductor Surfaces
The preparation of high-quality semiconductor field emission tips appears to be more difficult than that of metal emitters. Although total energy distributions of the emitted electrons from clean and well-defined crystallographic planes have been obtained (see Sections 8.5 and 8.6), the amount of such data is still very small. This is unfortunate because, as we hope to demonstrate in the present chapter, a lot of interesting physics can be learned from such studies. Obviously, the energy distribution of the emitted electrons can provide us with information on the surface density of states, as in the case of metal emitters. In the case of semiconductors, however, and in contrast to the situation in metal emitters, it cannot always be assumed that the occupation of the one-electron states under conditions appropriate to a field emission experiment is the same as in equilibrium (zero emitted current). Thus a new dimension is introduced in the field emission process which leads, or may lead, to new phenomena which do not occur in field emission from metal surfaces (see Sections 8.6 and 8.7). Even in the absence of nonequilibrium effects (i.e., at sufficiently low emitted currents) the theory is not as straightforward as for metal emitters, because of field penetration into the semiconductor which leads to band bending at the surface.
KeywordsConduction Band Valence Band Fermi Level Surface State Tunneling Current
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