Antiperovskite materials are of high research interest because of their unusual physical properties and technological applications. Here, we report the structural stability and transport properties of Sr3AsN from first-principles study. The calculated equilibrium lattice parameters are in good agreement with the available data. We find that Sr3AsN is mechanically, energetically and dynamically stable at ambient conditions. Our calculated electronic structure indicates that it is a direct band gap semiconductor, with a band gap value ∼1.2 eV. Sr-4d and N-2p orbitals predominantly contribute to the formation of the direct band gap. The calculated Seebeck coefficient of Sr3AsN is high (298 μV/K at 300 K), while the lattice thermal conductivity is comparatively low (1.73 W/m K). The considerable mass difference between Sr, As, and N gives rise to an intense phonon scattering that results in such low lattice thermal conductivity. Our calculated maximum thermoelectric figure of merit (ZT) is 0.75 at 700 K, indicating that it is a potential material for thermoelectric device applications.

Electronic structures of single crystal pentacene are of great interest for the elucidation of charge carrier transport in organic semiconductor materials. Experimental observation of valence band dispersion was recently achieved on single crystal samples of pentacene; however, its intrinsic properties are still unresolved because past experiments were performed on specimens with surface oxides formed by exposure to the ambient atmosphere. In this work, X-ray photoelectron spectroscopy (XPS) and angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) were conducted on single-crystal pentacene samples prepared without ambient exposure. The XPS results confirmed the reduction of the abundance of oxide impurities on the present samples. The ARUPS measurements clearly resolved the valence band structures of the single-crystal pentacene in four symmetry directions of the surface Brillouin zone, indicating anisotropy of at least a factor of 2.4 for the intermolecular transfer integral and hole effective mass at the valence band maximum.

A brief review on the present knowledge of the electronic properties of the Ga(In)NAs ternary and quaternary alloys is given mainly from an experimental perspective. The discussion is focused on Ga(In)NAs with low N composition (< 10 %), where a large amount of experimental work has been done. Important fundamental electronic properties of the material system are analyzed with the emphasis on the nature of the giant band gap bowing in the alloy and nitrogen-induced modifications of the electronic structure of the conduction band. The current knowledge of the key material parameters, relevant for the device applications, such as electron effective mass, recombination processes and band alignment in Ga(In)NAs/GaAs heterostructures, is also reviewed.

We report on the application of infrared spectroscopic ellipsometry (IR-SE) for wavenumbers from 333cm−1 to 1200cm−1 as a novel approach to non-destructive optical characterization of free-carrier and optical phonon properties of group III-nitride heterostructures. Undoped α-GaN, α-AlN, α-AlxGa1−xN (x = 0.17, 0.28, 0.5), and n-type silicon (Si) doped α-GaN layers were grown by metal-organic vapor phase epitaxy (MOVPE) on c-plane sapphire (α-Al2O3). The four-parameter semi-quantum (FPSQ) dielectric lattice-dispersion model and the Drude model for free-carrier response are employed for analysis of the IR-SE data. Model calculations for the ordinary (∈⊥) and extraordinary (∈||) dielectric functions of the heterostructure components provide sensitivity to IR-active phonon frequencies and free-carrier parameters. We observe that the α-AlxGa1−xN layers are unintentionally doped with a back ground free-carrier concentration of 1–4 1018cm−3. The ternary compounds reveal a two-mode behavior in ∈⊥, whereas a one-mode behavior is sufficient to explain the optical response for ∈||. We further provide a precise set of model parameters for calculation of the sapphire infrared dielectric functions which are prerequisites for analysis of infrared spectra of III-nitride heterostructures grown on α-Al2O3.