Electron Emission, Electroluminescence, and Voltage-Controlled Negative Resistance in Al–Al2O3–Au Diodes

Abstract

The temperature dependence of the conductivity of Al–Al₂O₃–Au diodes that exhibit voltage‐controlled negative resistance (VCNR) in their current‐voltage (I‐V) characteristics, as well as electron emission and electroluminescence from such diodes, have been studied. Electron emission into vacuum and electroluminescence are both characterized by a steep increase in intensity for diode voltages greater than 1.8 V. Electron emission exhibits a second rise when the diode voltage exceeds the work function of the metal facing vacuum; electroluminescence, in contrast, is quenched when the diode voltage exceeds about 4V. The resistance of Al–Al₂O₃–Au diodes is independent of temperature down to 3°K if V_m, the voltage for maximum current in the I‐V characteristic, is not exceeded. If the full I‐V characteristic is traced out as temperature is decreased, diode resistance increases, VCNR in the I‐V characteristic disappears, and electron emission into vacuum from the diode disappears. The attenuation length for electrons emitted into vacuum through the gold films of Al–Al₂O₃–Au diodes is ∼200 Å, independent of diode voltage; the attenuation length in the oxide is greater than 200 Å. Retarding potential measurements of the normal energy component of emitted electrons, and electroluminescence of diodes, show that some electrons gain energies in the oxide film that are higher than the applied voltage. The maximum excess energy gained is 4.1 V. Electroluminescence occurs from spots on Al–Al₂O₃–Au diodes. The spectrum covers the visible range with peaks of higher intensity at 1.8, 2.3, and 4.0 V. The experimental data are used to derive values of the parameters of a proposed model of VCNR in metal‐insulator‐metal diodes.