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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.


FE-SEM (45° tilted view) and TEM images of the InAs nanowires grown for 7 min on Si(111) substrates. Nanowires were (a) grown at 530°C (sample A), (b) grown at 550°C (sample B), (c) grown at 570°C (sample C); (d) low-resolution TEM image of the nanowire. (e) High-resolution image of a portion of the nanowires. The inset of (a) shows a higher magnification image of sample A; the inset of (b) is a top view image; the inset of (e) shows the fast Fourier transform of the selected area on (e), which is viewed along the 0 [1-11] direction.
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Figure 1: FE-SEM (45° tilted view) and TEM images of the InAs nanowires grown for 7 min on Si(111) substrates. Nanowires were (a) grown at 530°C (sample A), (b) grown at 550°C (sample B), (c) grown at 570°C (sample C); (d) low-resolution TEM image of the nanowire. (e) High-resolution image of a portion of the nanowires. The inset of (a) shows a higher magnification image of sample A; the inset of (b) is a top view image; the inset of (e) shows the fast Fourier transform of the selected area on (e), which is viewed along the 0 [1-11] direction.

Mentions: Figure 1 shows the SEM images of samples A, B, and C. It is observed that vertical and uniform InAs NWs with hexagonal cross sections are obtained in all the three samples. With few exceptions, all InAs NWs are grown along the < 111 > direction, which is perpendicular to Si substrate surface. No large base islands are observed at the base area surrounding NWs' root, which is different from the case of catalyst-assisted growth of NWs where large base islands are usually observed [9]. This suggests a different growth mechanism for catalyst-free InAs NWs compared with catalyst-assisted InAs NWs. According to previous work [5], the large lattice mismatch between InAs and Si could be the driving force for such catalyst-free NW growth. InAs clusters/islands first nucleate in Volmer-Weber mode on Si, where uniform film growth is prohibited due to the large interfacial energy. Then, to relax the strain energy in the system, the InAs material is preferred to grow vertically and form NWs. The few large InAs islands and non-vertical InAs NWs observed in sample A, B, and C can be explained by the reoxidation in the system, which provides nucleation sites and reactant sinks and also assist in the growth of larger InAs islands and non-vertical NWs [5,16].


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)

FE-SEM (45° tilted view) and TEM images of the InAs nanowires grown for 7 min on Si(111) substrates. Nanowires were (a) grown at 530°C (sample A), (b) grown at 550°C (sample B), (c) grown at 570°C (sample C); (d) low-resolution TEM image of the nanowire. (e) High-resolution image of a portion of the nanowires. The inset of (a) shows a higher magnification image of sample A; the inset of (b) is a top view image; the inset of (e) shows the fast Fourier transform of the selected area on (e), which is viewed along the 0 [1-11] direction.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: FE-SEM (45° tilted view) and TEM images of the InAs nanowires grown for 7 min on Si(111) substrates. Nanowires were (a) grown at 530°C (sample A), (b) grown at 550°C (sample B), (c) grown at 570°C (sample C); (d) low-resolution TEM image of the nanowire. (e) High-resolution image of a portion of the nanowires. The inset of (a) shows a higher magnification image of sample A; the inset of (b) is a top view image; the inset of (e) shows the fast Fourier transform of the selected area on (e), which is viewed along the 0 [1-11] direction.
Mentions: Figure 1 shows the SEM images of samples A, B, and C. It is observed that vertical and uniform InAs NWs with hexagonal cross sections are obtained in all the three samples. With few exceptions, all InAs NWs are grown along the < 111 > direction, which is perpendicular to Si substrate surface. No large base islands are observed at the base area surrounding NWs' root, which is different from the case of catalyst-assisted growth of NWs where large base islands are usually observed [9]. This suggests a different growth mechanism for catalyst-free InAs NWs compared with catalyst-assisted InAs NWs. According to previous work [5], the large lattice mismatch between InAs and Si could be the driving force for such catalyst-free NW growth. InAs clusters/islands first nucleate in Volmer-Weber mode on Si, where uniform film growth is prohibited due to the large interfacial energy. Then, to relax the strain energy in the system, the InAs material is preferred to grow vertically and form NWs. The few large InAs islands and non-vertical InAs NWs observed in sample A, B, and C can be explained by the reoxidation in the system, which provides nucleation sites and reactant sinks and also assist in the growth of larger InAs islands and non-vertical NWs [5,16].

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.