Ammonothermal Synthesis of Earth-Abundant Nitride Semiconductors ZnSiN and ZnGeN and Dissolution Monitoring by In Situ X-ray Imaging.

In this contribution, first synthesis of semiconducting ZnSiN and ZnGeN from solution is reported with supercritical ammonia as solvent and KNH as ammonobasic mineralizer. The reactions were conducted in custom-built high-pressure autoclaves made of nickel-based superalloy. The nitrides were characterized by powder X-ray diffraction and their crystal structures were refined by the Rietveld method. ZnSiN (a=5.24637(4), b=6.28025(5), c=5.02228(4) Å, Z=4, R =0.0556) and isotypic ZnGeN (a=5.46677(10), b=6.44640(12), c=5.19080(10) Å, Z=4, R =0.0494) crystallize in the orthorhombic space group Pna2 (no. 33). The morphology and elemental composition of the nitrides were examined by electron microscopy and energy-dispersive X-ray spectroscopy (EDX). Well-defined single crystals with a diameter up to 7 μm were grown by ammonothermal synthesis at temperatures between 870 and 1070 K and pressures up to 230 MPa. Optical properties have been analyzed with diffuse reflectance measurements. The band gaps of ZnSiN and ZnGeN were determined to be 3.7 and 3.2 eV at room temperature, respectively. In situ X-ray measurements were performed to exemplarily investigate the crystallization mechanism of ZnGeN . Dissolution in ammonobasic supercritical ammonia between 570 and 670 K was observed which is quite promising for the crystal growth of ternary nitrides under ammonothermal conditions.