**2. The growth**

The growth of high-quality nanowires should be achieved by avoiding the common growth process that employs a foreign catalyst such as gold to nucleate the wires. Au is well known to introduce deep level traps in the material band gap as contaminations [36, 37], which then limits the performance of the devices functionality on Si. Therefore, using lithographically predefined SiO<sup>2</sup> template is an additional benefit besides avoiding catalysts which enables an accurate control over positions and diameters of the grown NWs that determines where the growth occurs and allows homogeneous arrays by controlling the nucleation position without any catalysts by the selective area epitaxy technique.

In this work, the selective area molecular beam epitaxy (SA-MBE) technique has been used as a first step to grow the InAsSb/InAs MQWs NWs on Si (111) wafers and was achieved with nano-hole patterns produced by EBL [38]. The substrate is masked with a patterned dielectric layer, normally a SiO<sup>2</sup> layer with a thickness below 100 nm. The NW growth starts when the As and In adatoms start to form critical nuclei of certain sizes on the surface inside the patterned holes.

substrate, and the final hole diameter was ~80 nm due to lateral etching. From the SEM images, the MQW wires were on average ~1.5 μm in length and ~100 nm in diameter, see

**Figure 1.** Nanowire structural design and analysis. (a) Schematic drawing of the InAsSb/InAs MQW within InAs NWs,

Blue and yellow spheres represent In and As atoms, respectively, while red spheres indicate the random incorporation of Sb within the quantum well region. (b and c) Top view and tilted view SEM images, respectively. The nanowires are viewed at an angle of 70°. The scale bars in (b) and (c) are 1 μm. Figure obtained with permission from authors [38].

template with 80-nm diameter holes.

Nanowires for Room-Temperature Mid-Infrared Emission

http://dx.doi.org/10.5772/intechopen.79463

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The lattice structure of the InAs/InAsSb MQW NWs has been investigated using Scanning Transmission Electron Microscopy (STEM). A close inspection of high-resolution STEM images shows both the angled nature of the well and a continued WZ structure within the InAsSb well. **Figure 2** shows a full diameter image of the wire together with a zoomed-in view, within which the lattice structure can be discerned. From the zoomed-in view, it is clear that the structure of the InAsSb well does not change to ZB, as it would do in a pure InAsSb NW. However, in the case of the QWs, the short growth durations are insufficient to allow a flat top to form and so the WZ phase is maintained. Hence, the Sb fraction in the wells is

currently best estimated at 6–7%, based on comparable bulk wires.

grown in a 330-nm pitch square array patterned on a silicon substrate using a SiO<sup>2</sup>

**Figure 1(b)** and **(c)**.

**3. Structural analysis**

The MQW nanowire growth was initiated by impinging As flux followed by exposure of the sample to the In flux 20 s later. After the growth of an initial pure InAs section for 1 h, the MQW active region was grown as 10 repeats of InAs/InAs1−xSb<sup>x</sup> MQWs with growth durations of 180 and 27 s, respectively. This was expected to form 10 repeats of 25 nm InAs and 8 nm InAs1−xSb<sup>x</sup> , giving a total active region thickness of 330 nm as shown in **Figure 1(a)**.

Finally, the wires were finished with an InAs cap, grown for 10 min. All growths began with a pure InAs section and were finished with an InAs cap. For further comparison, a planar bulk InAs sample was grown as a reference under the same growth conditions. The MQW NWs were grown in arrays of 50-nm diameter holes patterned using e-beam lithography in a 330-nm pitch square array defined within a number of 200 × 200 μm areas, on each silicon

**Figure 1.** Nanowire structural design and analysis. (a) Schematic drawing of the InAsSb/InAs MQW within InAs NWs, grown in a 330-nm pitch square array patterned on a silicon substrate using a SiO<sup>2</sup> template with 80-nm diameter holes. Blue and yellow spheres represent In and As atoms, respectively, while red spheres indicate the random incorporation of Sb within the quantum well region. (b and c) Top view and tilted view SEM images, respectively. The nanowires are viewed at an angle of 70°. The scale bars in (b) and (c) are 1 μm. Figure obtained with permission from authors [38].

substrate, and the final hole diameter was ~80 nm due to lateral etching. From the SEM images, the MQW wires were on average ~1.5 μm in length and ~100 nm in diameter, see **Figure 1(b)** and **(c)**.
