Formation energies and chemical potential diagrams of II-Ge-N2 semiconductors

III-Nitride wide band gap semiconductors are well known for optoelectronic and electronic applications. They however have disadvantages, for example, the high cost of Indium, difficulties of p-type doping and phase separation in their alloys. In this work, the novel II-Ge-N-2 semiconductors that are related to III-N by replacing the group-III with a group-II (Mg and Cd) and a group-IV (Ge) are investigated. The lattice parameters of the II-Ge-N-2 are predicted by a full potential linear muffin-tin orbital (FP-LMTO) approach within the generalized gradient approximation (GGA). The results are also compared with those of ZnGeN2. Furthermore, the formation energies of the new materials and their competing compounds, such as Zn3N2, Mg3N2, Cd3N2 and Ge3N4, are calculated from the constituent elements. The chemical potential diagrams for stability, which are constructed from the calculated formation energies, facilitate us to determine the allowed ranges of the chemical potentials of the elements where the compounds are stable at zero temperature and pressure.