Increase in Current Density at Metal/GeO2/n-Ge Structure by Using Laminated Electrode
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In a metal/n-Ge structure, Fermi level pinning tends to occur. The insertion of an oxide layer at the interface between electrodes and n-Ge can effectively reduce the Schottky barrier height. However, the attachment of metal and oxide can cause diffusion of oxygen to the metal due to Gibbs free energy, which degrades the contact characteristics. In this study, we investigated the effects of a laminated electrode on the current density at a metal/GeO2/n-Ge structure. Ni, Pt, Al, or Ti layers with thicknesses of 0.5–20 nm were formed, followed by a deposition of 200-nm-thick Al. The J–V curves of these samples showed that the current density of the Al/Ti/GeO2/n-Ge structure was the largest among them and was about 126 times larger than that of the Al/GeO2/n-Ge structure. We also found that the current density depended on the film thickness of Ti and was the highest at the film thickness of about 2.5 nm or less. To investigate the effect of the Ti interlayer on the current density, we obtained the depth profiles of X-ray photoelectron spectroscope spectra of the Al/Ti/GeO2/n-Ge and Al/GeO2/n-Ge structures. Analysis showed that the diffusion of the oxygen to Al was limited by the 20-nm-thick Ti, and the oxygen was diffused to Al when the film thickness of Ti was about 1 nm. These results demonstrate that laminated oxide structures such as AlOx/TiOx and TiOx/GeO2 can form on the sample with 1-nm-thick Ti, which increases the current density.
KeywordsPinning n-Ge Laminated electrode Ti GeO2
This research and development was supported by MIC/SCOPE #165103005. The work was partly carried out in the Advanced ICT Devices Lab at NICT.
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