Ammonothermal Synthesis of Earth-Abundant Nitride Semiconductors ZnSiN2 and ZnGeN2 and Dissolution Monitoring by In Situ X-ray Imaging

5 years ago

Ammonothermal Synthesis of Earth-Abundant Nitride Semiconductors ZnSiN2 and ZnGeN2 and Dissolution Monitoring by In Situ X-ray Imaging

Peter Wellmann, Jonas Häusler, Wolfgang Schnick, Saskia Schimmel

In this contribution, first synthesis of semiconducting ZnSiN2 and ZnGeN2 from solution is reported with supercritical ammonia as solvent and KNH2 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. ZnSiN2 (a=5.24637(4), b=6.28025(5), c=5.02228(4) Å, Z=4, Rwp=0.0556) and isotypic ZnGeN2 (a=5.46677(10), b=6.44640(12), c=5.19080(10) Å, Z=4, Rwp=0.0494) crystallize in the orthorhombic space group Pna21 (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 ZnSiN2 and ZnGeN2 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 ZnGeN2. 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. Ammonothermal: Ternary semiconducting Zn-IV-nitrides ZnSiN2 and ZnGeN2 were synthesized in supercritical ammonia with alkali metal amides as mineralizers. The crystallization mechanism was examined by in situ X-ray visualization using custom-built high-pressure optical cells equipped with specially designed sapphire windows.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701081