Conduction-band effective mass and bandgap of ZnSnN2 earth-abundant solar absorber

Abstract

Pseudo III-V nitride ZnSnN2 is an earth-abundant semiconductor with a high optical absorption coefficient in the solar spectrum. Its bandgap can be tuned by controlling the cation sublattice disorder. Thus, it is a potential candidate for photovoltaic absorber materials. However, its important basic properties such as the intrinsic bandgap and effective mass have not yet been quantitatively determined. This paper presents a detailed optical absorption analysis of disordered ZnSnN2 degenerately doped with oxygen (ZnSnN2-x O x ) in the ultraviolet to infrared region to determine the conduction-band effective mass (m c∗) and intrinsic bandgap (E g). ZnSnN2-x O x epilayers are n-type degenerate semiconductors, which exhibit clear free-electron absorption in the infrared region. By analysing the free-electron absorption using the Drude model, m c∗ was determined to be (0.37 ± 0.05)m 0 (m 0 denotes the free electron mass). The fundamental absorption edge in the visible to ultraviolet region shows a blue shift with increasing electron density. The analysis of the blue shift in the framework of the Burstein-Moss effect gives the E g value of 0.94 ± 0.02 eV. We believe that the findings of this study will provide important information to establish this material as a photovoltaic absorber.