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Visible and infrared emission from Si/Ge nanowires synthesized by metal-assisted wet etching.

Irrera A, Artoni P, Fioravanti V, Franzò G, Fazio B, Musumeci P, Boninelli S, Impellizzeri G, Terrasi A, Priolo F, Iacona F - Nanoscale Res Lett (2014)

Bottom Line: In particular, we prepared ultrathin Si/Ge NWs having a mean diameter of about 8 nm and lengths spanning from 1.0 to 2.7 μm.NW diameter is compatible with the occurrence of quantum confinement effects and, accordingly, we observed light emission assignable to the presence of Si and Ge nanostructures.PACS: 61.46.Km; 78.55.-m; 78.67.Lt.

View Article: PubMed Central - HTML - PubMed

Affiliation: IPCF CNR, viale F, Stagno d'Alcontres 37, Faro Superiore, Messina 98158, Italy. irrera@its.me.cnr.it.

ABSTRACT
Multi-quantum well Si/Ge nanowires (NWs) were realized by combining molecular beam epitaxy deposition and metal-assisted wet etching, which is a low-cost technique for the synthesis of extremely dense (about 1011 cm-2) arrays of NWs with a high and controllable aspect ratio. In particular, we prepared ultrathin Si/Ge NWs having a mean diameter of about 8 nm and lengths spanning from 1.0 to 2.7 μm. NW diameter is compatible with the occurrence of quantum confinement effects and, accordingly, we observed light emission assignable to the presence of Si and Ge nanostructures. We performed a detailed study of the photoluminescence properties of the NWs, with particular attention to the excitation and de-excitation properties as a function of the temperature and of the excitation photon flux, evaluating the excitation cross section and investigating the presence of non-radiative phenomena. PACS: 61.46.Km; 78.55.-m; 78.67.Lt.

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Scheme of the fabrication of Si/Ge NWs. (a) The starting MQW consists of alternating 1-nm-thick Ge layers and 54-nm-thick Si layers, grown by MBE. This unit is repeated 62 times. (b) Deposition of an Au thin layer (2 nm) by EBE. (c) Formation of Si/Ge NWs by dipping the sample in an aqueous solution of HF and H2O2. (d) Removal of Au particles by using an aqueous solution of KI + I2. Steps (b,c,d) are performed at room temperature.
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Figure 1: Scheme of the fabrication of Si/Ge NWs. (a) The starting MQW consists of alternating 1-nm-thick Ge layers and 54-nm-thick Si layers, grown by MBE. This unit is repeated 62 times. (b) Deposition of an Au thin layer (2 nm) by EBE. (c) Formation of Si/Ge NWs by dipping the sample in an aqueous solution of HF and H2O2. (d) Removal of Au particles by using an aqueous solution of KI + I2. Steps (b,c,d) are performed at room temperature.

Mentions: Si/Ge NWs were obtained starting from a Si/Ge MQW grown by MBE on a (001) Si substrate at a temperature of 450°C, consisting of alternating Si (54-nm thick) and Ge (1-nm thick) layers (Figure 1a) deposited at a rate of 0.3 and 0.01 nm · s−1, respectively. The Si/Ge stack is repeated 62 times, giving an overall sample thickness of about 3.5 μm. Due to the relatively low-growth temperature, the Ge layers show an excellent pseudomorphic two-dimensional heteroepitaxy, as demonstrated by the in situ reflection high-energy electron diffraction (RHEED) image shown in Figure 2, while a transition to Stransky-Krastanov Ge island regime would have been taken place for the same Ge thickness at higher temperatures [15]. The samples were UV oxidized and dipped in 5% HF to obtain a clean and oxide-free surface. Afterward, a thin Au layer, having a thickness of 2 nm, was deposited on the MQWs at room temperature by electron beam evaporation (EBE), by using high-purity (99.9%) Au pellets as a source (Figure 1b). After Au deposition, the sample surface consisted of nanometric uncovered Si areas, almost circular and totally embedded within the Au regions. The samples were then etched at room temperature at a rate of 0.13 μm · min−1 in an aqueous solution of HF (5 M) and H2O2 (0.44 M) to form Si/Ge NWs (Figure 1c). Finally, the removal of the Au particles was carried out by dipping the sample in a KI + I2 aqueous solution (Figure 1d).


Visible and infrared emission from Si/Ge nanowires synthesized by metal-assisted wet etching.

Irrera A, Artoni P, Fioravanti V, Franzò G, Fazio B, Musumeci P, Boninelli S, Impellizzeri G, Terrasi A, Priolo F, Iacona F - Nanoscale Res Lett (2014)

Scheme of the fabrication of Si/Ge NWs. (a) The starting MQW consists of alternating 1-nm-thick Ge layers and 54-nm-thick Si layers, grown by MBE. This unit is repeated 62 times. (b) Deposition of an Au thin layer (2 nm) by EBE. (c) Formation of Si/Ge NWs by dipping the sample in an aqueous solution of HF and H2O2. (d) Removal of Au particles by using an aqueous solution of KI + I2. Steps (b,c,d) are performed at room temperature.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3928609&req=5

Figure 1: Scheme of the fabrication of Si/Ge NWs. (a) The starting MQW consists of alternating 1-nm-thick Ge layers and 54-nm-thick Si layers, grown by MBE. This unit is repeated 62 times. (b) Deposition of an Au thin layer (2 nm) by EBE. (c) Formation of Si/Ge NWs by dipping the sample in an aqueous solution of HF and H2O2. (d) Removal of Au particles by using an aqueous solution of KI + I2. Steps (b,c,d) are performed at room temperature.
Mentions: Si/Ge NWs were obtained starting from a Si/Ge MQW grown by MBE on a (001) Si substrate at a temperature of 450°C, consisting of alternating Si (54-nm thick) and Ge (1-nm thick) layers (Figure 1a) deposited at a rate of 0.3 and 0.01 nm · s−1, respectively. The Si/Ge stack is repeated 62 times, giving an overall sample thickness of about 3.5 μm. Due to the relatively low-growth temperature, the Ge layers show an excellent pseudomorphic two-dimensional heteroepitaxy, as demonstrated by the in situ reflection high-energy electron diffraction (RHEED) image shown in Figure 2, while a transition to Stransky-Krastanov Ge island regime would have been taken place for the same Ge thickness at higher temperatures [15]. The samples were UV oxidized and dipped in 5% HF to obtain a clean and oxide-free surface. Afterward, a thin Au layer, having a thickness of 2 nm, was deposited on the MQWs at room temperature by electron beam evaporation (EBE), by using high-purity (99.9%) Au pellets as a source (Figure 1b). After Au deposition, the sample surface consisted of nanometric uncovered Si areas, almost circular and totally embedded within the Au regions. The samples were then etched at room temperature at a rate of 0.13 μm · min−1 in an aqueous solution of HF (5 M) and H2O2 (0.44 M) to form Si/Ge NWs (Figure 1c). Finally, the removal of the Au particles was carried out by dipping the sample in a KI + I2 aqueous solution (Figure 1d).

Bottom Line: In particular, we prepared ultrathin Si/Ge NWs having a mean diameter of about 8 nm and lengths spanning from 1.0 to 2.7 μm.NW diameter is compatible with the occurrence of quantum confinement effects and, accordingly, we observed light emission assignable to the presence of Si and Ge nanostructures.PACS: 61.46.Km; 78.55.-m; 78.67.Lt.

View Article: PubMed Central - HTML - PubMed

Affiliation: IPCF CNR, viale F, Stagno d'Alcontres 37, Faro Superiore, Messina 98158, Italy. irrera@its.me.cnr.it.

ABSTRACT
Multi-quantum well Si/Ge nanowires (NWs) were realized by combining molecular beam epitaxy deposition and metal-assisted wet etching, which is a low-cost technique for the synthesis of extremely dense (about 1011 cm-2) arrays of NWs with a high and controllable aspect ratio. In particular, we prepared ultrathin Si/Ge NWs having a mean diameter of about 8 nm and lengths spanning from 1.0 to 2.7 μm. NW diameter is compatible with the occurrence of quantum confinement effects and, accordingly, we observed light emission assignable to the presence of Si and Ge nanostructures. We performed a detailed study of the photoluminescence properties of the NWs, with particular attention to the excitation and de-excitation properties as a function of the temperature and of the excitation photon flux, evaluating the excitation cross section and investigating the presence of non-radiative phenomena. PACS: 61.46.Km; 78.55.-m; 78.67.Lt.

No MeSH data available.


Related in: MedlinePlus