A method for improving the quality of heterointerfaces which has been increasingly investigated is selective area epitaxy (SAE) as it can help reduce interface defect formation and defect propagation between layers. SAE relies on a mask layer, such as silicon dioxide, patterned with (nano)holes where the growth is limited to under appropriate growth conditions. First, by reducing the area of the holes down to the nanoscale it can have a significant impact in the defect formation mechanisms, such as misfit dislocations, during epitaxial growth. Moreover, any threading dislocations will also be stopped by the mask layer, significantly reducing the amount propagating into the epilayer. SAE therefore holds potential in facilitating the epitaxial growth of materials lacking a lattice matched substrate as well as allowing for new material combinations for enhanced photovoltaic device performance. However, most of the techniques used for SAE using nanoscale holes rely on low-throughput techniques, such as molecular beam epitaxy and electron beam lithography. In our recent work we have shown how to overcome these limitations using e.g. metalorganic chemical vapour deposition (MOCVD) and Talbot Displacement lithography for the case of the earth-abundant photovoltaic absorber zinc phosphide (Zn₃P₂).

Zn₃P₂ is an emerging photovoltaic absorber for single-junction devices with a direct bandgap (1.5 eV) and other promising optoelectronic properties. However, its large lattice parameter and coefficient of thermal expansion has complicated its incorporation in heterojunctions, while the lack of controlled n-type doping has hindered the creation of homojunctions. Previous work has shown that SAE allows for high quality epitaxial growth of Zn₃P₂ nanopyramids and textured thin films. Unfortunately, the approach used relied on the aforementioned low-throughput techniques in addition to the use of scarce elements (In) in the substrate. In our recent work we have demonstrated how to overcome the first two limitations through the compatibility of SAE grown Zn₃P₂ with MOCVD, as well as scaling the nanopatterned areas using Talbot Displacement lithography. Through a combinatorial study we have explored the effect of temperature, precursor partial pressures and pitch on factors such as growth selectivity, defect formation and functional properties that were evaluated using a range of microscopy and spectroscopy techniques.