Controlled nanoscale epitaxial nucleation and growth has been shown to inhibit different defect formation mechanisms.[1,2] This has opened up the exploration of materials that were limited when grown using standard bulk techniques. One such material is zinc phosphide (Zn3P2), which despite promising properties has had limited success due to challenges related to its lattice structure, coefficient of thermal expansion, and lack of controlled doping.[3,4,5] Recently, selective area epitaxy (SAE) using nanoscale holes in a silicon dioxide mask to limit epitaxial growth to certain regions was shown to demonstrate high-quality zinc phosphide. [6] The reduced interface area helped reduce the interface defect formation and the epilayer became fully relaxed as it outgrew the hole. Moreover, as the material grew it also laterally overgrew the mask layer (later overgrowth epitaxy, LEO) and coalesced into a thin film. Zinc phosphide grows in a pyramidal shape during SAE, and laterally overgrows into a thin film with pyramidal texture, ideal for light trapping and photovoltaic applications.
    While promising, the initial demonstration of this approach with zinc phosphide relied on scarce elements (indium in the indium phosphide substrate), as well as low throughput techniques (molecular beam epitaxy and electron beam lithography). To show the scalability and transferability of SAE of photovoltaic absorbers we are therefore developing this approach using metalorganic vapour phase epitaxy (MOVPE) and Talbot displacement lithography that allow for large-scale and high throughput growth.[7] Furthermore, the next step is to replace the substrate with more earth-abundant alternatives (e.g. silicon) to improve the potential sustainability impact of the process. Using electron microscopy we investigate the morphological and structural properties of the SAE grown zinc phosphide, which is combined with photoluminescence spectroscopy as an initial qualitative assessment of the functional properties and crystal quality.

References
[1] F. Glas Phys. Rev. B, 2006, 74, 121302.
[2] M. T. Björk et al. Appl. Phys. Lett., 2002, 80, 1058.
[3] G. M. Kimball et al. Appl. Phys. Lett., 2009, 95, 112103.
[4] M. Y. Swinkels et al. Phys. Rev. Applied, 2020, 14, 024045.
[5] S. Escobar Steinvall et al. ACS Appl. Energ. Mater., 2022, 5, 5298–5306.
[6] S. Escobar Steinvall et al. Nanoscale Advances, 2020, 3, 326.
[7] V. J. Gómez et al. Nanotechnology, 2020, 31, 295301.