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We demonstrate that excitons in semiconductor alloys are subject to competing localization effects due to disorder (random potential fluctuations) and shallow point defects (impurities). The relative importance of these effects varies with alloy chemical composition, impurity activation energy as well as temperature. We evaluate this effect quantitatively for MgxZn1−xO : Al (0 6 x 6 0.058) and find that exciton localization at low (2 K) and high (300 K) temperatures is dominated by shallow donor impurities and alloy disorder, respectively.

The global increase in internet usage requires an upgrade of the existing infrastruc- ture. Lasers are a key proponent to improving existing systems, and engineering better gain materials aids in this effort. (InGa)As is the leading material in this field for 1.55 μm communication wavelengths, but can be improved on by changing the substrate from InP to GaAs. Another improvement would be reducing the losses due to Auger recombination. (InGa)(BiAs) is suggested to alleviate many of these issues, as it can be grown on a GaAs substrate and is capable of decreased Auger recombination. By analyzing prospective alloys (and existing ones) using spatial electron localization, a superior candidate for industrial use can be suggested. The localization captures the disorder introduced by alloying and can be associated with material properties such as the gain characteristics and photoluminescence linewidths. These properties are important factors in determining a successor. The subject of two-dimensional materials is another topic which has shown promise in various applica- tions. Examples include flexible, transparent, and miniaturized electronics. Recent research done by Al Balushi et al. suggests that GaN may be stabilized in a two-dimensional sys- tem. By extending the material modelling approach from the telecommunication application to this system, we were able to show which III-V isoelectronic elements can be substituted into GaN. This two-dimensional system may be the only candidate capable of spanning the visible spectrum. We found Phosphorus to be the strongest candidate for decreasing the band gap. / Thesis / Master of Applied Science (MASc)

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