Probing lattice dynamics in ST 12 phase germanium nanowires by Raman spectroscopy

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Applied Physics Letters, Volume 119, issue 23
Germanium (Ge) plays a crucial role in setting up important functionalities for silicon-compatible photonics. Diamond cubic germanium is an extensively studied semiconductor, although its other exotic forms, like BC8, ST8, ST12 phases, may possess distinct electronic properties. We have fabricated stable ST12-Ge nanowires via a self-seeded bottom-up three phase growth in a confined supercritical toluene environment. Here, we report on the direct evidence of the presence of the ST12 phase by a combination of Raman spectroscopy and first-principles calculations using density functional theory (DFT). It is important to remark that the DFT calculation predicts all the Raman active optical phonon modes of the P 4321 structure, and it is in very good agreement with the experimental results. The phonon dynamics as a function of temperature is investigated through Raman measurements at temperatures varying from 80 to 300 K. First-order temperature coefficients for all the observed Raman modes are estimated from the linear temperature dependence of the phonon shifts. A complete set of isobaric Grüneisen parameters is reported for all Raman modes of ST12-Ge nanowire, and the values are lower compared to the same for Si, dc-Ge bulk, and Ge nanowire. These results have important implications for understanding thermal properties of ST12-Ge nanowire.
The authors acknowledge financial support from Science and Engineering Research Board (SERB), India (File No. EMR/2017/ 002107). S.B., A.G., and J.D.H. acknowledge Science Foundation Ireland (Grant No. 14/IA/2513). Divya Srivastava would like to acknowledge CSC—the Finnish IT Center for Science for computational resources.
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Raha , S , Srivastava , D , Biswas , S , Garcia-Gil , A , Karttunen , A J , Holmes , J D & Singha , A 2021 , ' Probing lattice dynamics in ST 12 phase germanium nanowires by Raman spectroscopy ' , Applied Physics Letters , vol. 119 , no. 23 , 232105 .