High electron mobility single-crystalline ZnSnN2 on ZnO (0001) substrates

Making a systematic effort, we have developed a single-crystalline ZnSnN2 on ZnO (0001) by reactive magnetron co-sputtering. Epitaxial growth was achieved at 350°C by co-sputtering from metal targets in nitrogen atmosphere, and confirmed by transmission electron microscopy (TEM) measurements. TEM verified that the layers are single-crystalline of hexagonal phase, exhibiting epitaxial relationship with the substrate described by: [11-20]ZnSnN2//[11-20]ZnO and [0001]ZnSnN2//[0001]ZnO. The screw-type threading dislocations originating from the ZnSnN2/ZnO interface were identified as dominant extended defects. More specifically, we report a pioneering measurement of the dislocation density in this material of 1.5 x 1011 cm-2. Even though, there is no literature data for direct comparison, such values are typical of heteroepitaxial growth of III-nitride layers without applying defect density reduction strategies. The films demonstrated high electron mobility of 39 cm2V−1s−1 and 63 cm2V−1s−1 for stoichiometric and Zn-rich layers, respectively, while the electron carrier density remained in the low 1019 cm-3 range as determined by the Hall effect measurements at room temperature. The optical bandgaps of 1.86 eV and 1.72 eV were determined for the stoichiometric and Zn-rich samples, respectively. As such, we conclude that ZnSnN2 is an earth-abundant, environmentally-friendly semiconductor and is a promising candidate for cost efficient components in optoelectronics and photovoltaics.