**8. Conclusion**

the QWs. The atmospheric water vapour absorption is again evident near 2.7 μm (0.459 eV)

**Figure 9** presents a comparison of the temperature quenching of the NW samples, where the superior performance of the InAsSb MQW NWs is clearly evident due to the increase in the

The temperature dependence of the peak energies for the NWs is shown in **Figure 10**. The dotted lines represent fitting of the results using the empirical Varshni equation. The values

values for bulk InAs; both the InAs and the InAsSb MQW NWs have a WZ crystal structure and consequently have a weaker dependence of band gap on temperature (lower value of *α*)

An Arrhenius plot is shown in **Figure 11** for the InAsSb MQW NWs from which an activation energy of 49 meV was obtained from the high-temperature region and ~5 meV for the low-temperature region. This is in approximate agreement with the confinement energy for thermal excitation of holes out of the QW (hole localisation energy of 34 meV) and electrons from the interface triangular QWs (<13 meV localisation energy), respectively. The activation energy of ~49 meV obtained from the Arrhenius plot is consistent with quenching due to carriers escaping confinement rather than Auger recombination and so provides indirect

(0), α and β) are given in **Table 1** along with reference

, α and β for the NW samples, compared

radiative emission rate and suppression of Auger recombination.

**Table 1.** Comparison of Varshni parameters. The fitted Varshni parameters E0

with published parameters for bulk InAs and InSb [54].

in all the spectra.

obtained for the fitting parameters (Eg

68 Nanowires - Synthesis, Properties and Applications

evidence for Auger suppression.

than the corresponding bulk ZB materials.

The development of quantum structures in NWs systems has shown the potential to extend the concept of band-gap engineering to optimise the building blocks of such systems, as well as allowing integrating these systems into the leading CMOS technology, providing a promising future for nanotechnology in optics and electronics. This chapter has presented InAsSb MQWs heterostructures within InAs NWs which exhibit mid-infrared emission at room temperature. The type II QWs provided quantum confinement and spatial localisation of the carriers combined with a suppression of Auger recombination, resulting in enhanced PL emission with respect to the bulk InAs NWs. Furthermore, having characterised the effect of charging on the type II QW, the flat-band transition energy was found to be in good agreement with calculations for both samples. These new quantum-structured NWs will allow novel nano-photonic and quantum light sources to be developed for the technologically important mid-infrared spectral range. They can exploit both the general advantages of site-controlled NWs, such as integration with silicon substrates, and also enhance light-matter coupling based on their dimensions and geometry, opening the way for a wide range of applications.
