Extensive studies have been conducted on dilute nitride III–V compounds (III–V-N alloys) due to their unique strong band gap bowing with a decrease in their lattice constant when nitrogen atoms are substituted for the group-V in a dilute regime. This has led to expectations for their use in a wide variety of optical and electronic device applications on various substrates. For instance, GaP-rich GaPAsN quaternary alloys are essential candidates for light-emitting and light absorbing devices on Si substrates because of their near-lattice matching to Si and widely tunable bandgap range, enabling current matching conditions for successful integration in tandem cell on Si platform.1 However, unintentional nitrogen-related point defects remain critical for the optical quality of III–V-N alloys, independent of growth technique. In the case of GaPAsN alloys, post-growth rapid thermal annealing (RTA) is effective for improving optical properties but it does so at the expense of an undesired increase in the energy band gap,2 especially at elevated temperatures > 700 oC, where the effect of annealing on PL enhancement is pronounced.

In a collaborative work comprising research groups from Romania, Japan and USA, 6-MeV electrons irradiation of a nearly lattice-matched P-rich GaPAsN-on-GaP epilayer, grown by molecular beam epitaxy, and subsequent rapid thermal annealing are found to induce much stronger photoluminescence than what is observed for an identical as-grown sample annealed in similar conditions. At the same time, exciton localization at low temperatures decreased and alloys crystallinity improved. These irradiation-related phenomena occured without change in the alloy macroscopic composition as revealed by X-ray diffraction. The next step is to apply this important finding for improving the optical performance of a solar cell structure including this GaPAsN quaternary alloy.  

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The estimated results

The estimated results of the project are:

1) Device-grade InGaN/BGaN superlattice (SL) heterostructures lattice compatible to GaN..
2) p-i-n GaN/InGaN/BGaN-SL/GaN solar cells (proof-of-concept).
3) 5  hihg-impact scientific publications.
4) 3 presentation at international conferenceslts