The Effects of Nitrogen Incorporation on Photogenerated Carrier Dynamics in Dilute Nitrides

The addition of small fractions of nitrogen to GaAs-based materials results in a significant reduction of the bandgap, opening up the potential for a range of electronic and optoelectronic applications. However, the addition of nitrogen also has a large impact on the carrier dynamics, often resulting in a considerable increase in shallow traps, which readily capture excitons. A number of mechanisms have been proposed to explain the creation of shallow traps, which give rise to localised states. Many of these are associated with deposition problems, such as well width fluctuations and compositional inhomogeneities, caused by the large miscibility gap associated with the incorporation of nitrogen. However, some of these growth issues are not intrinsic to dilute nitrides and advances in deposition technology have shown that these associated problems can be significantly reduced. In this chapter, we will give an overview of how the incorporation of nitrogen into dilute nitrides affects carrier dynamics. This will include detailed discussion about the experimental evidence for exciton trapping presented in the scientific literature, such as the so-called S-shape temperature dependence of photoluminescence emission, lineshapes and radiative decay rates. We will also review the various mechanisms which have been put forward to account for the exciton trapping and discuses how/if these can be overcome.