The band gap of the chalcopyrite and spalerite phases of epitaxial ZnSnP$_{2}$

Using contactless electroreflectance, we accurately determined the band gap of the two known phases of epitaxial ZnSnP$_{2}$. Induced by small changes in Sn/Zn flux ratio during epitaxy, the order-disordered transition between the chalcopyrite and sphalerite phases considerably affects the band gap energy. The chalcopyrite ordered phase, unambiguously identified from x-ray diffraction of sphalerite forbidden reflection peaks, exhibits a band gap of 1.67 eV at 293K. A small splitting of this transition is observed at 80K, indicating the presence of a crystal field produced by a small tetragonal distortion and a deviation from the ideal c/a=2 ratio. The band gap of the disordered sphalerite phase is 1.38 eV, somewhat higher than the value of 1.32 eV reported from bulk crystals, indicating either a remaining trace of ordering or a slight deviation from stoichiometry. Tailoring the electronic and optical properties of ZnSnP$_{2}$ at a fixed composition through an ordered- disordered transition has interesting technological applications. For example, it is an interesting material for multijunction solar cells because of its non-toxicity, abundance and low-cost.