Temperature-dependent Fowler–Nordheim tunneling and a compensation effect in anodized Al-Al2O3-Au diodes

Current-voltage (I–V) curves of Al-Al2O3-Au diodes with anodized Al2O3 thicknesses between 12 and 54nm have been measured between 100 and 320K. Diodes are rectifying at 300K. There is a marked decrease in rectification of I–V curves as temperature decreases from 300to100K. Part of the decrease is due to a decrease in current when Au is positive (applied voltage VA>0V); part of the decrease is due to an increase in current for VA<0V as temperature decreases. A reversal of the rectification direction has been observed at 100K. I–V curves for increasing VA>0V are affected by the polarization of the diode by a negative voltage. I–V curves for decreasing VA are independent of previous history and are due to Fowler–Nordheim tunneling, J=CF2exp(−B∕F). Values of B and C are temperature dependent. B is used to obtain an effective barrier height for tunneling, ϕE. ϕE increases from ∼1.5to∼2.5eV as temperature decreases from 300to100K for VA>0V. For VA<0V, ϕE∼2.3eV at 100K and increases to ∼2.8eV at 160K, except for the diode with 12nm of Al2O3. There is a relation between B and C lnC=r+sB, where r and s are constants, which is analogous to a compensation effect or Meyer–Neldel relation for data that obey an Arrhenius equation. A model is proposed in which the tunnel barrier is determined by an impurity band in Al2O3.