Solid-State Field-Controlled Electron Emission: An alternative to thermionic and field-emission
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Solid-State Field-Controlled Electron Emission: an alternative to thermionic and field-emission Vu Thien Binh, J.P. Dupin, P. Thevenard, D. Guillot and J.C. Plenet Laboratoire d’Emission Electronique, DPM-CNRS, University Claude Bernard Lyon 1, 69622, Villeurbanne, France. ABSTRACT In the solid-state field-controlled emitter (SSE), the emission barrier, which is the factor of utmost importance for surface electron emission, is tailored by a controlled extrinsic parameter like the injected space charge located near the surface. This is done by depositing an ultra-thin wide band-gap semiconductor layer on a metallic surface. It is an alternative approach to the thermionic or field emission for which the work function value is intrinsic to the material used. The emission current measurements from the SSE cold cathodes show stable emission, at low applied field (≈50 V/µm) and in poor vacuum (≈10-7 Torr). The new emission mechanism has been modeled, the calculations and the theoretical analysis confirm the experimental results. The fabrication of the SSE, either by a sputter deposition in vacuum or by a sol-gel technique, meets most of the demands specific to high throughput fabrication of cold cathodes with large emitting area dedicated to applications in vacuum microelectronics. INTRODUCTION As a paradigm shift for surface electron emission, we proposed the solid-state fieldcontrolled emitter (SSE) [1]. The basic structure of SSE is an ultra-thin wide bandgap n-type semiconductor (UTSC) layer deposited on a metallic surface (Fig. 1). The electron emission from the SSE cathodes results from a serial two-step mechanism: the first step is the injection of electrons at the solid-state Schottky junction from the metal into the UTSC medium, followed by a second step which is the electron emission from the UTSC surface that becomes, under the control of an applied field Fapp, a surface with a low electron affinity (LEA) or with a negative electron affinity (NEA). The injected charges induce a large band bending in the UTSC layer, with consequence a drastic lowering of the emission barrier ∆ΦE (∆ΦE is the potential difference between the metal Fermi level and the vacuum level). ∆ΦE can become low enough to allow emission of electrons through it (LEA situation for ∆ΦE ≤ 2 eV) or over it (NEA situation for ∆ΦE ≤ 0). This emission concept differs from conventional electron emission mechanisms, such as thermionic and field emission, for which to obtain emission current it is necessary to apply either high temperature (>2000 K) or high field (>5000 V/µm) to overcome the work function which is fixed by the nature of the solid, the crystallography and the adsorption state of the cathode surface.
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Figure 1. Schematic draw of the SSE structure with an UTSC layer deposited on a metallic surface. The metal plays the role of an electron reservoir and the electrons are emitted from the UTSC surface. THE SSE CONCEPT FOR SURFACE ELECTRON EMISSION The conventional thermionic and field emission To obtain emission, it is necessary to re
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