Electronic structure of germanium nitride considered for gate dielectrics

First-principles calculations based on density-functional theory and the local-density approximation have been used to investigate structural, electronic, and optical properties of α, β, and γ phases of germanium nitride (Ge3N4). β-Ge3N4 was found to be the most stable among the three structures, and it has a very small lattice mismatch with Ge, which indicates that it could be grown epitaxially on Ge. The calculated band gaps of α-, β-, and γ-Ge3N4 are about 3.15, 3.07, and 2.33eV, and the corresponding static dielectric constants are 4.70, 4.74, and 6.27, respectively, within local-density approximation. Results of our calculations indicate that the band gap and static dielectric constants of Ge3N4, as well as Si3N4, could satisfy the requirements of gate dielectrics for Ge-based field effect transistors.