In this paper, we demonstrate that it is possible to synthesize light-emitting Si/Ge NWs by LY2109761 in vitro metal-assisted wet etching of Si/Ge MQW grown by molecular
beam epitaxy (MBE) on a Si substrate. We report a detailed study on the structural and optical properties of this system which, remarkably, exhibits both visible (due to Si) and infrared (IR; due to Ge) light emissions. Methods 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 . 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 CP-868596 mw 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). 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 Apoptosis inhibitor 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. Figure 2 RHEED analysis of the grown MQW. The image shows spots of the 2 × 1 surface reconstruction (black arrows) superimposed to those of the initial 1 × 1 symmetry (white arrows). The presence of this diffraction pattern guarantees for a clean surface and a good two-dimensional epitaxial growth. NW structural characterization was performed by scanning electron microscopy (SEM) and Raman spectroscopy. SEM analyses were performed using a field emission Zeiss Supra 25 microscope (Oberkochen, Germany).