Review: Structural properties of binary metal nitrides

Thin films of binary metal nitrides with cubic or hexagonal crystal structures have a wide range of industrial applications. Their potential and that of their alloys range from metallic protective coatings for cutting tools and quantum wells in light-emitting devices to current-carrying channels in high-frequency and power transistors, as well as piezoelectric actuators and resonators in microelectromechanical and acoustic components. For the epitaxy of the required films and layer structures as well as for the design of metal nitride-based piezoelectric, electronic, and optoelectronic devices, precise knowledge of their structural properties is particularly important. It is, therefore, surprising that simulated and experimental data on lattice parameters, even for binary nitrides that have been studied for many years, differ too widely or are not sufficiently consistent for targeted design, e.g., for piezoelectric resonators with applications in future mobile communication systems. This review combines two complementary approaches to select and improve the accuracy and consistency of the physical data. First, based on a search of published data and supplementary simulations, two cubic (rock-salt and zinc-blende) and two hexagonal crystal structures (layered hexagonal and wurtzite) are described for each binary metal nitride, regardless of whether the respective crystal lattices are mechanically and thermodynamically stable under normal conditions. Second, all metal nitrides present in these crystal lattices, from the metal atomic number of 5 for BN to 81 for TlN, are comparatively examined. The systematic comparison of the structural properties of related cubic and hexagonal crystal structures of each binary metal nitride, combined with comparing different metal nitrides with each other by varying the atomic number of the metal atom over a wide range, reveals a clear dependence of the lattice parameters, bond lengths, nearest neighbor metal–metal distances, average volumes required per atom, and mass densities on the electron configuration of the metal atoms. In particular, the systematic changes in the structural properties of binary metal nitrides, whose metal atoms belong to the same period or group in the periodic table of elements, are presented here and are used to determine improved data sets of structural parameters.