ZnSiP2 Thin Film Growth for Si-Based Tandem Photovoltaics

ZnSiP 2 is a ternary III-V analog with 0.5% lattice mismatch with Si and a 2.1 eV band gap, in the appropriate range for a top cell on a Si-based tandem device. We have previously shown that ZnSiP 2 has many properties suitable for applications to Si-based tandem photovoltaics using bulk single crystals grown in a Zn flux. The favorable results obtained from characterization of bulk material encourage the development of ZnSiP 2 as a photovoltaic absorber. To pursue this development, we have constructed a thin film growth reactor. This reactor employs a combination of chemical vapor deposition, using silane and phosphine as precursor gases, and physical vapor deposition, using an effusion cell to evaporate elemental Zn. We will present the results of ZnSiP 2 film growth on (100) Si substrates. The composition, structure, and morphology of these films have been characterized by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron diffraction, and electron microscopy, respectively. These promising results represent significant advancement towards implementing ZnSiP 2 as a top cell material on Si-based tandem photovoltaics.