The electronic band structure of Ga(PAsN) with a few percent of nitrogen is calculated in the whole composition of Ga(PAs) host using the state-of-the-art density functional methods including the modified Becke-Johnson functional to correctly reproduce the band gap, and band unfolding to reveal the character of the bands within the entire Brillouin zone. As expected, relatively small amounts of nitrogen introduced to Ga(PAs) lead to formation of an intermediate band below the conduction band which is consistent with the band anticrossing model, widely used to describe the electronic band structure of dilute nitrides. However, in this study calculations are performed in the whole Brillouin zone and reveal the significance of correct description of the band structure near the edges of Brillouin zone, especially for indirect band gap P-rich host alloy, which may not be properly captured with simpler models. The theoretical results are compared with experimental studies, confirming their reliability. The influence of nitrogen on the band structure is discussed in terms of application of Ga(PAsN) in optoelectronic devices such as intermediate band solar cells and light emitters. It is found that Ga(PAsN) with low N and As concentration has a band structure suitable for integration in Si tandem solar cells, since the lattice mismatch between Si and Ga(PAsN) is small in this case. Moreover, it is concluded that P-rich Ga(PAsN) alloys with low N concentration have a promising band structure for two colour emitters. Additionally, the effect of nitrogen incorporation on the carrier localization is studied and discussed.
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