Potential pathway for the formation of ZnMN₂ (M = Si, Ge) from zinc carbodiimide and group 14 oxides using a facile process

Abstract

III–N-type (III = Al, Ga, and In) compounds are applied to various semiconductor and optical devices, such as LEDs and solar cells. Owing to their similar structures and electronic and electrical properties to those of III–N-type compounds, II–IV–N₂-compounds (II = Zn, Mg, and Mn; IV = Si, Ge, and Sn) are expected to become next-generation semiconductor materials. However, they possess low thermal stability, and their synthesis requires high-energy and complex processes that use high-pressure fields or high-vacuum environments. In this study, we investigated a new process to easily and quickly synthesize II–IV–N₂-compounds under ambient pressure using carbodiimide compounds and group 14 oxides as raw materials. The resulting ZnGeN₂ was successfully synthesized after heating a mixed powder of zinc carbodiimide and germanium oxide to 650–850 °C under a nitrogen atmosphere. In particular, zinc carbodiimide reacted with germanium oxide in the solid phase to produce ZnGeN₂, with CO₂ as a by-product. Thus, the high thermal stability of the generated CO₂ contributed to the reaction progressing at low temperatures, suggesting a mechanism similar to that of the solid-state metathesis reaction. When a mixed powder of zinc carbodiimide and silicon dioxide were heated to 850–1050 °C under a nitrogen atmosphere, ZnSiN₂ phase was successfully synthesized. The cyanogen and zinc vapors formed via the thermal decomposition of zinc carbodiimide contributed to its formation. We demonstrated that zinc carbodiimide functioned as an effective nitrogen and metal source to form ZnMN₂ (M = Si and Ge), although the reaction mechanisms of Si- and Ge-containing ZnMN₂ were different. Our proposed method is effective for the simple and rapid synthesis of ZnMN₂-type compounds from stable raw material systems. These characteristics are advantageous compared to the current complicated and time-consuming processes.