Electroluminescence and Conduction in Nb–Nb2O5–Au Diodes

Abstract

Three experiments—current-voltage characteristics, electroluminescence, and photoconductivity—are consistent with the hypothesis that both holes and electrons can be injected into Nb–Nb2O5–Au diodes whose thickness varies between 90 and 3500 Å. Such diodes are strongly rectifying. For some diodes with oxide films thinner than 300 Å, J ∝ exp(eV/2kT) for diode voltages between 0.3 and 0.8 V. For oxide films thicker than 1000 Å, J ∝ V3/L5 for diode voltages greater than 1.2 V. Electroluminescence is observed from thin Nb–Nb2O5–Au diodes under forward bias at applied voltages of 1.2 V. The energy of the emitted radiation is ∼1.2 eV, independent of oxide thickness. The threshold for photoconductivity of Nb–Nb2O5–Au diodes is also ∼1.2 eV. It is proposed that an impurity band occurs in Nb2O5, 1.2 eV below the conduction band. Hole injection into the impurity band depends on the work function of the counterelectrode metal Au. Replacement of Au by a low-work-function metal, In, eliminates evidence for double injection in the insulator. Rectification is negligible in Nb–Nb2O5–In diodes. At low diode voltages, J ∝ V/L5; at higher diode voltages, J ∝ V2/L6.