Hot-Electron Transport in Al–Al2O3 Triodes Produced by Plasma Oxidation

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Abstract
The measurement of tunnel triodes by a small ac signal r parameter technique is shown to give a new way of directly measuring the oxide barrier height and barrier asymmetry. This type of measurement permits distinguishing between true hot‐electron collection and leakage currents. A saturation of the hot electron transport coefficient has been found vs the emitter‐base bias. The most direct explanation for this saturation is that those hot electrons which are collected are mainly ballistic, i.e., that they have come from the emitter with little or no momentum change due to collisions. The Al base attenuation length has been measured to be 150 Å at 77°K for electrons 2.0 eV above the Fermi level. Collector‐voltage dependence of the triode has been explained on the basis of electron‐phonon losses in the collector oxide. The major part of the large hot electron attenuation factor in these triodes cannot be explained by either metal base losses or electron‐phonon losses in the oxides, which together give rise to an attenuation factor of ≈ (¼) in a typical triode. An interfacial loss mechanism appears to be the most likely explanation for the large attenuation factor of ≈ (1/100) remaining after taking the above volume losses into account.

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