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

当在Al/AlO_x/Ag结上施加足够强但不超过金属功函数的电压时，可以产生能量高于费米能级的所谓“热电子”。在本研究中，我们旨在建立Al/AlO_x/Ag结的制备方法，并通过测量I-V曲线来了解隧道结和多孔硅衬底界面上热电子的行为。此外，利用红外反射吸收光谱研究了外加偏压时银电极表面化学物种的变化。主要研究结果如下：(1)Al/AlO_x/Ag隧道结制备的关键是确定Al薄膜电极的氧化条件。铝电极在氧气气氛中氧化2小时，或在空气中氧化几分钟是合适的。(2)在441.6 nm He-Cd激光(80 MW)照射下，多孔硅衬底上形成的结的隧道电流显著增加，而玻璃衬底上形成的结即使在相同的辐照条件下，隧道电流也没有变化。本文所用多孔硅的带隙约为1.6 eV，因此在多孔硅上产生的光电压可能通过改变铝电极和多孔硅衬底之间的电荷分布来影响结的隧穿特性。(3)在铝电极上施加偏置电压(+)可以促进结上形成的2-甲基-1，4-萘醌薄膜的分解。

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.