Inelastic Tunneling Due to Vibrational Modes of Yttrium and Chromium Oxides

Previous measurements of the tunneling spectra (d²IdV² versus applied voltage) of metaloxide-metal tunnel diodes have revealed the presence of structure due to the interaction of tunneling electrons with vibrational impurities contained within the oxide region. New observations with diodes of the type Y-(Y oxide)-metal and Cr-(Cr oxide)-metal reveal relatively intense structure in the range 0-100 mV which we associate with vibrational modes of the oxides themselves. Experimental evidence indicates that the structure is not due to the metal electrodes. The new spectra are comparable with infrared absorption data taken for oxide films grown at low temperatures. For both cases, the structure corresponds to an increase in conductance of slightly less than 1%, and is therefore comparable in intensity to molecular inelastic tunneling spectra. Cr oxide barriers grown at elevated temperatures (200 ^∘{}C) on films produced in good vacuum (10^-7 Torr) do not exhibit the "giant" resistance anomaly at zero bias.