Behavior of hot-electron at MIM tunnel junction/porous Si interface

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When a sufficiently strong voltage but not beyond the metal work function is applied across an Al/AlO_x/Ag junction, the so-called "hot-electron" whose energy is higher than the Fermi level can be generated. In this study, we aimed to establish the method of fabrication of Al/AlO_x/Ag junctions and to obtain basic knowledge concerning the behavior of hot electrons at the interface between the tunnel junction and the porous-Si substrate through measurements of the I-V curve. Further, the change in chemical species on Ag electrode surface during a bias voltage was applied across the junction was investigated with IR reflection absorption spectroscopy. The results obtained are summarized as follows.(1)A matter of the utmost importance in preparation of the Al/AlO_x/Ag tunnel junction is to establish the oxidation conditions of Al thin film electrode. The oxidation of the Al electrode at 280℃, 2 hours in oxygen (1 atm) atmosphere, or at 450℃, several minutes in air was suitable to obtain the junction.(2)Under irradiation of 441.6nm He-Cd laser (80mW), a remarkable increase in the tunnel current was observed for the junction formed on porous-Si substrate, whereas the junction formed on glass substrate showed no change in the tunnel current even though the same irradiation conditions were employed. The band-gap of the porous-Si used in the present study was about 1.6 eV and hence the photo-voltage generated at the porous-Is might influence the tunneling properties of the junction through the change in charge distribution between the Al electrode and the porous-Si substrate.(3)The decomposition of a 2Methyl-1, 4Naphtoquinone thin film formed on the junction was promoted when applying the bias voltage (+) to the Al electrode.