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Effect of growth temperature on the morphology and phonon properties of InAs nanowires on Si substrates.

Li T, Chen Y, Lei W, Zhou X, Luo S, Hu Y, Wang L, Yang T, Wang Z - Nanoscale Res Lett (2011)

Bottom Line: It is found that both the density and length of InAs NWs decrease with increasing growth temperatures, while the diameter increases with increasing growth temperature, suggesting that the catalyst-free growth of InAs NWs is governed by the nucleation kinetics.A surface optical mode is also observed for the InAs NWs, which shifts to lower wave-numbers when the diameter of NWs is decreased, in agreement with the theory prediction.A splitting of TO modes is also observed.PACS: 62.23.Hj; 81.07.Gf; 63.22.Gh; 61.46.Km.

View Article: PubMed Central - HTML - PubMed

Affiliation: Key Laboratory of Semiconductor Material Science, Institute of Semiconductors, Chinese Academy of Science, Beijing 100083, People's Republic of China. yhchen@semi.ac.cn.

ABSTRACT
Catalyst-free, vertical array of InAs nanowires (NWs) are grown on Si (111) substrate using MOCVD technique. The as-grown InAs NWs show a zinc-blende crystal structure along a < 111 > direction. It is found that both the density and length of InAs NWs decrease with increasing growth temperatures, while the diameter increases with increasing growth temperature, suggesting that the catalyst-free growth of InAs NWs is governed by the nucleation kinetics. The longitudinal optical and transverse optical (TO) mode of InAs NWs present a phonon frequency slightly lower than those of InAs bulk materials, which are speculated to be caused by the defects in the NWs. A surface optical mode is also observed for the InAs NWs, which shifts to lower wave-numbers when the diameter of NWs is decreased, in agreement with the theory prediction. The carrier concentration is extracted to be 2.25 × 1017 cm-3 from the Raman line shape analysis. A splitting of TO modes is also observed.PACS: 62.23.Hj; 81.07.Gf; 63.22.Gh; 61.46.Km.

No MeSH data available.


Related in: MedlinePlus

Raman spectra of InAs NWs measured with different average diameter and theoretical prediction. (a) Raman spectra from InAs NWs with average diameters from 35 nm (red), 42 nm (black), and 70 nm (blue). The lighter colored (green) lines are results from a multiple Lorentzian fit. The vertical line is a guide to the eye. The position of SO phonon down shifts with the decrease in diameter; (b) Dependence of the position of the SO phonon from the diameter of the NWs. The points represent experimental data obtained from several measured samples with different average diameters. The line corresponds to the theoretical prediction for cylindrical InAs NWs.
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Figure 3: Raman spectra of InAs NWs measured with different average diameter and theoretical prediction. (a) Raman spectra from InAs NWs with average diameters from 35 nm (red), 42 nm (black), and 70 nm (blue). The lighter colored (green) lines are results from a multiple Lorentzian fit. The vertical line is a guide to the eye. The position of SO phonon down shifts with the decrease in diameter; (b) Dependence of the position of the SO phonon from the diameter of the NWs. The points represent experimental data obtained from several measured samples with different average diameters. The line corresponds to the theoretical prediction for cylindrical InAs NWs.

Mentions: Apart from sample B, Raman experiments are also performed on sample A and C. Figure 3 shows Raman spectra of InAs NWs measured with incident laser beam parallel to the c-axis of NWs at room temperature. As stated above, the phonon peaks on low energy side of LO phonon modes are from SO phonon modes. Obviously, the SO phonon peak shifts toward lower energy side with reducing NWs' diameter. More interestingly, for InAs NWs with smaller diameters (larger surface-to-volume ratio), the SO phonon mode can be more clearly distinguished. These features further indicate that the Raman peak located between TO and LO phonon peaks can, indeed, be attributed to the scattering from surface phonons. According to the model stated above, the phonon frequency of SO mode can be calculated according to the diameter of NWs. Figure 3b shows the calculated phonon frequency of SO mode in InAs NWs with various diameters and the experimentally measured phonon frequency of SO mode of InAs NWs in sample A, B, and C. Obviously, the experimental values agree well with the theoretical values, confirming the SO mode origin of the Raman peak between LO and TO phonon peaks.


Effect of growth temperature on the morphology and phonon properties of InAs nanowires on Si substrates.

Li T, Chen Y, Lei W, Zhou X, Luo S, Hu Y, Wang L, Yang T, Wang Z - Nanoscale Res Lett (2011)

Raman spectra of InAs NWs measured with different average diameter and theoretical prediction. (a) Raman spectra from InAs NWs with average diameters from 35 nm (red), 42 nm (black), and 70 nm (blue). The lighter colored (green) lines are results from a multiple Lorentzian fit. The vertical line is a guide to the eye. The position of SO phonon down shifts with the decrease in diameter; (b) Dependence of the position of the SO phonon from the diameter of the NWs. The points represent experimental data obtained from several measured samples with different average diameters. The line corresponds to the theoretical prediction for cylindrical InAs NWs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211884&req=5

Figure 3: Raman spectra of InAs NWs measured with different average diameter and theoretical prediction. (a) Raman spectra from InAs NWs with average diameters from 35 nm (red), 42 nm (black), and 70 nm (blue). The lighter colored (green) lines are results from a multiple Lorentzian fit. The vertical line is a guide to the eye. The position of SO phonon down shifts with the decrease in diameter; (b) Dependence of the position of the SO phonon from the diameter of the NWs. The points represent experimental data obtained from several measured samples with different average diameters. The line corresponds to the theoretical prediction for cylindrical InAs NWs.
Mentions: Apart from sample B, Raman experiments are also performed on sample A and C. Figure 3 shows Raman spectra of InAs NWs measured with incident laser beam parallel to the c-axis of NWs at room temperature. As stated above, the phonon peaks on low energy side of LO phonon modes are from SO phonon modes. Obviously, the SO phonon peak shifts toward lower energy side with reducing NWs' diameter. More interestingly, for InAs NWs with smaller diameters (larger surface-to-volume ratio), the SO phonon mode can be more clearly distinguished. These features further indicate that the Raman peak located between TO and LO phonon peaks can, indeed, be attributed to the scattering from surface phonons. According to the model stated above, the phonon frequency of SO mode can be calculated according to the diameter of NWs. Figure 3b shows the calculated phonon frequency of SO mode in InAs NWs with various diameters and the experimentally measured phonon frequency of SO mode of InAs NWs in sample A, B, and C. Obviously, the experimental values agree well with the theoretical values, confirming the SO mode origin of the Raman peak between LO and TO phonon peaks.

Bottom Line: It is found that both the density and length of InAs NWs decrease with increasing growth temperatures, while the diameter increases with increasing growth temperature, suggesting that the catalyst-free growth of InAs NWs is governed by the nucleation kinetics.A surface optical mode is also observed for the InAs NWs, which shifts to lower wave-numbers when the diameter of NWs is decreased, in agreement with the theory prediction.A splitting of TO modes is also observed.PACS: 62.23.Hj; 81.07.Gf; 63.22.Gh; 61.46.Km.

View Article: PubMed Central - HTML - PubMed

Affiliation: Key Laboratory of Semiconductor Material Science, Institute of Semiconductors, Chinese Academy of Science, Beijing 100083, People's Republic of China. yhchen@semi.ac.cn.

ABSTRACT
Catalyst-free, vertical array of InAs nanowires (NWs) are grown on Si (111) substrate using MOCVD technique. The as-grown InAs NWs show a zinc-blende crystal structure along a < 111 > direction. It is found that both the density and length of InAs NWs decrease with increasing growth temperatures, while the diameter increases with increasing growth temperature, suggesting that the catalyst-free growth of InAs NWs is governed by the nucleation kinetics. The longitudinal optical and transverse optical (TO) mode of InAs NWs present a phonon frequency slightly lower than those of InAs bulk materials, which are speculated to be caused by the defects in the NWs. A surface optical mode is also observed for the InAs NWs, which shifts to lower wave-numbers when the diameter of NWs is decreased, in agreement with the theory prediction. The carrier concentration is extracted to be 2.25 × 1017 cm-3 from the Raman line shape analysis. A splitting of TO modes is also observed.PACS: 62.23.Hj; 81.07.Gf; 63.22.Gh; 61.46.Km.

No MeSH data available.


Related in: MedlinePlus