Combinatorial Investigation of the Mn-Ge-N Chemical System Containing Ternary Nitrides Mn3GeN and MnGeN2

By changing nitrogen chemical potential during synthesis of Mn-Ge-N ternary nitrides, both wurtzite MnGeN2 and antiperovskite Mn3GeN ternary phases are prepared. Antiperovskite films are optically opaque and conductive, while wurtzite films with Mn/(Mn + Ge) <= 0.5 transmit light above ~ 2 eV. Alloys of Mn3GeN with Si and Al are also investigated. Mn3(Ge1-xAlx)N alloys with 0.07 <= x <= 0.16 exhibit a cubic (rather than tetragonal) structure. Mn3(Ge1-xSix)N with x <= 0.05 maintains the tetragonal structure but becomes cubic when x > 0.05. This study shows that care must be taken in the synthesis of Mn-Ge-N and similar nitrides, especially when materials are integrated into devices not amenable to structural and chemical probing.