A family of novel three-terminal devices which relies on the transfer of a quasi-monoenergetic hot electron beam through a thin base is described. The devices are similar in principle to the proposed tunneling amplifier by Mead in the early sixties (“Cold Cathode” or “Metal Base” amplifiers). Results are reviewed and the probable reasons for the poor performances are pointed out. It is predicted that, with a proper choice of parameters, metal-base amplifiers can operate as switches, negative resistance devices and continuous amplifiers in the subpicosecond range. Two subclasses are described: The tunneling emitter (THETA), in the major part of the work, and the nontunneling emitter (BHETA) amplifiers. In the THETA family the metal-oxide-metal-oxide-metal (MOMOM), the MOM-semiconductor (MOMS), and the heterojunctions devices are described. Members of the BHETA family generate quasi-monoenergetic electron beams by injecting electrons by an n + n − or a metal- n − junctions, and include a variety of metals and semiconductor combinations. Very thin films are required in these devices (oxides ∼15 A, metals ∼100 A, semiconductors ∼100 A). The molecular beam epitaxy technique and lattice matching considerations are required for pinhole free semiconductors and metal films with minimum interface states. Sputter-oxidation methods are needed for thin oxide growth. Systems which combine these features with availability of microfabrication make these devices feasible today.

Tunneling hot electron transfer amplifiers (theta): Amplifiers operating up to the infrared

A variety of scattering processes occur within the metal—oxide—metal tunnel cathode, with the result that most of the injected electrons fail to escape into vacuum. By considering the over‐all behavior it is possible to identify the most important loss mechanisms and where they occur.Electron emission measurements suggest that the internal hot electron velocity distribution in the exit metal films is isotropic as a result of numerous phonon scattering events. It is also found that the electron attenuation length in the exit metal film is not a strong function of energy over most of the observable range. As a direct consequence one obtains the result that the shape and mean energy of the emitted electron energy distribution are determined principally by the scattering in the oxide layer. Collision ionization is unlikely; hence optical phonon scattering is believed to be the principal oxide energy loss mechanism. If the scattering is random and independent of energy, both the mean energy loss (ΔE) and mean ...

Hot Electron Energy Loss in Tunnel Cathode Structures

Hot electron transport and emission have been studied for Au-SiO-Au thin film cold cathodes with oxide thicknesses in the range 100–6400 A. The devices were observed to undergo an electro-forming process on application of a d.c. bias, as described previously. Electron attenuation lengths in the gold layer were found to be in the range 1000–3000 A and to increase with applied bias, in strong contrast with tunnel cathode structures. Attenuation lengths in the oxide layer were ∼ 700 A. Electrons were emitted with energies up to the full applied bias and it is estimated that these electrons can acquire excess energies of up to 4·7 eV by excitation in the oxide layer. No correlation was observed between the areas of the devices yielding electroluminescence and electron emission.

Hot electron transport and emission in Au-SiO-Au thin film cathodes

Thin‐film electron emitters are described, which operate below 200°K and below a limiting critical applied voltage (νc) in a stable temperature‐independent regime. Current‐voltage characteristics and normal electron energy distributions are presented. Fabrication and operation criteria are outlined. Comparison with temperature‐dependent emitters is made, and possible conduction mechanisms discussed briefly.

/pdf/cryogenic-thin-film-electron-emitters-3ioqgvxphd.pdf

Cryogenic thin‐film electron emitters

Low Energy Electron Mean Free Paths in Solids1

Retarding-field measurements are reported of the energy distribution of electrons emitted from AlAl 2 O 3 Al tunnel cathodes, in which the oxide layer was formed to a thickness ∼100 A by anodization. On the assumption of a spherically symmetrical distribution within the positive aluminium layer, the energetic electrons therein were found to have exponential distributions in energy, with temperatures in the range (2500, 4000°K) depending on bias field and distance from the oxide-metal interface. The attenuation length for electron-electron scattering in aluminium was found to decrease with increasing energy of the hot electrons. The energy distribution of emitted electrons was conditioned principally by scattering processes at high fields (several MV cm −1 ) in the oxide layer; a theory of this process is given. The mean free path in the amorphous Al 2 O 3 amounted to 5 A.

The transport of hot electrons in AlAl2O3Al tunnel cathodes

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The transport of hot electrons in AlAl2O3Al tunnel cathodes