Ammonothermal Synthesis and Optical Properties of Ternary Nitride Semiconductors Mg‐IV‐N₂, Mn‐IV‐N₂ and Li‐IV₂‐N₃ (IV=Si, Ge)

Abstract

Abstract Grimm–Sommerfeld analogous nitrides MgSiN 2 , MgGeN 2 , MnSiN 2 , MnGeN 2 , LiSi 2 N 3 and LiGe 2 N 3 (generally classified as II‐IV‐N 2 and I‐IV 2 ‐N 3 ) are promising semiconductor materials with great potential for application in (opto)electronics or photovoltaics. A new synthetic approach for these nitride materials was developed using supercritical ammonia as both solvent and nitride‐forming agent. Syntheses were conducted in custom‐built high‐pressure autoclaves with alkali metal amides LiNH 2 , NaNH 2 or KNH 2 as ammonobasic mineralizers, which accomplish an adequate solubility of the starting materials and promote the formation of reactive intermediate species. The reactions were performed at temperatures between 870 and 1070 K and pressures up to 230 MPa. All studied compounds crystallize in wurtzite‐derived superstructures with orthorhombic space groups Pna 2 1 (II‐IV‐N 2 ) and Cmc 2 1 (I‐IV 2 ‐N 3 ), respectively, which was confirmed by powder X‐ray diffraction. Optical bandgaps were estimated from diffuse reflectance spectra using the Kubelka–Munk function (MgSiN 2 : 4.8 eV, MgGeN 2 : 3.2 eV, MnSiN 2 : 3.5 eV, MnGeN 2 : 2.5 eV, LiSi 2 N 3 : 4.4 eV, LiGe 2 N 3 : 3.9 eV). Complementary DFT calculations were carried out to gain insight into the electronic band structures of these materials and to corroborate the optical measurements.