Temperature dependence of voltage-controlled negative resistance and electroluminescence in Al-Al2O3-Au diodes

Voltage-controlled negative resistance (VCNR) and unipolar resistive switching that can be used for memory applications can develop in the current-voltage (I-V) curves of metal-insulator-metal diodes. Electroluminescence is intimately connected with the occurrence of VCNR in I-V curves. The temperature dependence of VCNR and electroluminescence of Al-Al2O3-Au diodes with anodic Al2O3 thicknesses between 12 and 54 nm has been studied between 300 and 180 K. There is a threshold voltage, V-th, for the occurrence of electroluminescence. V-th is between 1.5 and 2.0 V at 300 K and is independent of Al2O3 thickness. As temperature is lowered, the maximum current of the I-V curve that exhibits VCNR, I-mx, decreases. The voltage for maximum current, V-mx, increases as does V-th. Around 200 K, currents become small and erratic; VCNR and electroluminescence disappear but reappear if the diode temperature is raised above similar to 200 K. Detailed measurements of the temperature dependence of I-mx, V-mx, and V-th are presented for Al-Al2O3-Au diodes with different anodic Al2O3 thicknesses. The relative electroluminescent intensity is largest in the thinnest samples. A model is proposed for conduction in a filamentary region of an Al-Al2O3-Au diode. Electrons injected into an impurity band in Al2O3 recombine with defect centers in Al2O3 to produce electroluminescence. Positively charged defect centers in Al2O3 cause the formation of an Ohmic contact and a high-field region at the Al-Al2O3 interface. The Ohmic contact, in turn, determines the I-V curves of a conducting channel. Recombination of electrons with defect centers that produce the Ohmic contact changes the Ohmic contact and causes the current decrease in the negative resistance region of the I-V curves.