Voltage-controlled negative resistance and electroluminescent spectra of Al–Al2O3–Au diodes

Dielectric breakdown of metal-insulator-metal (MIM) diodes can result in the development of voltage-controlled negative resistance (VCNR) in the current-voltage (I-V) characteristics. Electroluminescence from the MIM diode appears at the same time as VCNR develops. The spectra of electroluminescence associated with VCNR of Al–Al2O3–Au diodes with anodic Al2O3 has been measured for photon energies between 1.8 eV, the lowest photon energy the photomultiplier can detect, and 3.4 eV, using narrow-band interference filters. Electroluminescent photons have maximum intensity between 1.8 and 2.4 eV with a peak at ∼2.2 eV. The voltage threshold for electroluminescence in Al–Al2O3–Au diodes, VTH, is 1.7 to 2.0 V; it is associated with an impurity band in amorphous Al2O3. Electrons injected into the impurity band can recombine with radiative centers in Al2O3 or can be emitted into vacuum. The range of values of VTH is the same as the range of values of the barrier height at the Al–Al2O3 interface measured by internal photo emission or by tunneling. The spectral data support a model of conduction and VCNR in a conducting channel. Dielectric breakdown and forming of VCNR introduce positive charge at the Al–Al2O3 interface that results in an Ohmic contact and a high field region in the conducting channel. Electrons injected into Al2O3 when the applied voltage is greater than VTH neutralize positive charge, change the Ohmic contact, and cause a decrease in current with increasing voltage. The radiative centers involved in electroluminescence are also responsible for other forms of luminescence in Al2O3.