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Efects of Low‑Temperature GeSn Bufer Layers on Sn Surface Segregation During GeSn Epitaxial Growth
Takahiro Tsukamoto,Nobumitsu Hirose,Akifumi Kasamatsu,Toshiaki Matsui,Yoshiyuki Suda 대한금속·재료학회 2020 ELECTRONIC MATERIALS LETTERS Vol.16 No.1
We investigate the efects of the low-temperature (LT) GeSn bufer layers on Sn surface segregation during the growth of the additional GeSn layers. Sn surface segregation was observed in the GeSn layers formed on Si substrates at the growth temperature of 300 °C. However, there was no Sn surface segregation in the GeSn layers grown at 300 °C on the LT GeSn bufer layers formed at 225 °C. The Sn surface segregation was limited by the efects of the LT bufer layers. Crystallinity of the GeSn layers grown at 300 °C on the LT GeSn bufer layers was investigated by Raman spectroscopy. The full width at half maximum of the Ge–Ge Raman spectrum obtained from the GeSn layers was about 3.1 cm−1, which means that the formed GeSn layers have excellent crystallinity. We have successfully demonstrated that the LT GeSn bufer layers can limit the Sn surface segregation, which increases the growth temperature and improves crystallinity of the GeSn layers.
Increase in Current Density at Metal/GeO2/n‑Ge Structure by Using Laminated Electrode
Takahiro Tsukamoto,Shota Kurihara,Nobumitsu Hirose,Akifumi Kasamatsu,Toshiaki Matsui,Yoshiyuki Suda 대한금속·재료학회 2020 ELECTRONIC MATERIALS LETTERS Vol.16 No.1
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 efectively reduce the Schottky barrier height. However, the attachment of metal and oxide can cause difusion of oxygen to the metal due to Gibbs free energy, which degrades the contact characteristics. In this study, we investigated the efects 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 flm thickness of Ti and was the highest at the flm thickness of about 2.5 nm or less. To investigate the efect of the Ti interlayer on the current density, we obtained the depth profles of X-ray photoelectron spectroscope spectra of the Al/Ti/GeO2/n-Ge and Al/ GeO2/n-Ge structures. Analysis showed that the difusion of the oxygen to Al was limited by the 20-nm-thick Ti, and the oxygen was difused to Al when the flm 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.