improving the thermoelectric figure of merit of ScN by electronic structure engineering through stoichiometry tuning and doping
For high performance thermoelectric devices, the materials need to be thermally stable at a large temperature gradient and
have a high ZT \cite{Kerdsongpanya_2012}
of first-principles full-potential linear muffin-tin orbital calculations of the elastic constants and related structural and electronic properties of BN, AlN, GaN, and InN in both the zinc-blende and wurtzite structures
related to strains along the c axis (C 13 and C 33 ) are found to be less accurate than the others.
Our results provide predictions for the remaining crystal structure materials combinations for which no direct experimental data are presently available
In order to model the behavior of the thin film heterostructures on which many electroluminescent devices ͓light emitting diodes ͑LED͒ and laser diodes͔ are based, a knowledge of their elastic constants and strain deformation potentials is indispensable. For example, the elastic constants
allow one to determine by continuum elasticity theory 6 the precise strain state of a pseudomorphic epitaxial thin film ͑which is under biaxial stress because it has to adapt to the substrate on which it is grown͒, or of a free standing superlattice of alternating thin layers of two of these binary materials.
the elastic constants may be needed to calculate the residual strain that may result from thermal expansion coefficient mismatch. In other words, films may be free of strain at the growth temperature but have a residual strain after cooling down. Once the strain state is determined,
the deformation potentials determine the changes in the band structure resulting from the strain in the materials. Likewise, for the applications of c-BN in hard coatings and other applications related to its hardness, its elastic constants are obviously important
Nevertheless, these properties are at present poorly known for all these materials. Although several total energy and band-structure calculations of the group III nitrides have recently been published ͑see, e.g., Ref. 7 for an overview͒, a systematic study of their elastic constants and behavior under hydrostatic and uniaxial stress has been lacking.
Until recently there were only a few fairly old experimental studies of the wurtzite nitrides ͑BN, GaN, and InN͒ ͑Ref. 8͒ which determined the elastic constants from rather indirect x-ray measurements on powders or crystals of rather poor quality. The values for cubic GaN and InN reported by Sherwin and Drummond 9 were obtained from these values by an appropriate rotation of the elasticity tensor for the hex-
agonal system. This procedure will be discussed below. Only recently have accurate values based on sound velocity or
related measurements been reported for AlN, 10,11 GaN, 12 and c-BN. 13 Accurate measurements are still lacking for InN.