Low-Temperature Surface Preparation and Epitaxial Growth of ZnS and Cu2ZnSnS4 on ZnS(110) and GaP(100)

We give a summary of the low-temperature preparation methods of ZnS(1 1 0) and GaP(1 0 0) crystals for epitaxial growth of ZnS and Cu₂ZnSnS₄ (CZTS) via molecular beam epitaxy. Substrates were prepared for epitaxial growth by means of room-temperature aqueous surface treatments and subsequent ultra-high vacuum transfer to the deposition system. Epitaxial growth of ZnS was successful at 500 K on both ZnS(1 1 0) and GaP(1 0 0) as only single domains were observed with electron backscatter diffraction; furthermore, transmission electron microscopy measurements confirmed an epitaxial interface. Epitaxial growth of CZTS was successful on ZnS at 700 K. However, epitaxial growth was not possible on GaP at 700 K due to Ga_xS_y formation, which significantly degraded the quality of the GaP crystal surface. Although CZTS was grown epitaxially on ZnS, growth of multiple crystallographic domains remains a problem that could inherently limit the viability of epitaxial CZTS for model system studies.