Spectra of surface plasmon polariton enhanced electroluminescence from electroformed Al-Al_2O_3-Ag diodes

摘要

Narrow band-pass filters have been used to measure the spectral distribution of electroluminescent photons with energies between 1.8 eV and 3.0 eV from electroformed Al-Al_2O_3-Ag diodes with anodic Al_2O_3 thicknesses between 12nm and 18nm. Electroforming of metal-insulator-metal (MIM) diodes is a non-destructive dielectric breakdown that results in a conducting channel in the insulator and changes the initial high resistance of the MIM diode to a low resistance state. It is a critical step in the development of resistive-switching memories that utilize MIM diodes as the active element. Electroforming of Al-Al_2O_3-Ag diodes in vacuum results in voltage-controlled negative resistance (VCNR) in the current-voltage (Ⅰ-Ⅴ) characteristics. Electroluminescence (EL) and electron emission into vacuum (EM) develop simultaneously with the current increase that results in VCNR in the Ⅰ-Ⅴ characteristics. EL is due to recombination of electrons injected at the Al-Al_2O_3 interface with radiative defect centers in Al_2O_3. Measurements of EL photons between 1.8 eV and 3.0 eV using a wide band-pass filter showed that EL intensity is exponentially dependent on Al_2O_3 thickness for Al-Al_2O_3-Ag diodes between 12nm and 20 nm thick. Enhanced El intensity in the thinnest diodes is attributed to an increase in the spontaneous emission rate of recombination centers due to high electromagnetic fields generated in Al_2O_3 when EL photons interact with electrons in Ag or Al to form surface plasmon polaritons at the Al_2O_3-Ag or Al_2O_3-Al interface. El intensity is a maximum at 2.0-2.2 eV for Al-Al_2O_3-Ag diodes with Al_2O_3 thicknesses between 12 nm and 18 nm. EL in diodes with 12 nm or 14 nm of Al_2O_3 is enhanced by factors of 8-10 over EL from a diode with 18 nm of Al_2O_3. The extent of EL enhancement in the thinnest diodes can vary significantly between samples. A narrow band of recombination centers was found in one Al-Al_2O_3-Ag diode with 12nm of Al_2O_3; it had EL intensity 100 times greater at 2.15 eV than the diode with 18nm of Al_2O_3. EL intensity for photons with energies greater than 2.6 eV is nearly the same for all diodes.