We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...

Band parameters for nitrogen-containing semiconductors

The hybrid two-dimensional (2D) halide perovskites have recently drawn significant interest because they can serve as excellent photoabsorbers in perovskite solar cells. Here we present the large scale synthesis, crystal structure, and optical characterization of the 2D (CH3(CH2)3NH3)2(CH3NH3)n−1PbnI3n+1 (n = 1, 2, 3, 4, ∞) perovskites, a family of layered compounds with tunable semiconductor characteristics. These materials consist of well-defined inorganic perovskite layers intercalated with bulky butylammonium cations that act as spacers between these fragments, adopting the crystal structure of the Ruddlesden–Popper type. We find that the perovskite thickness (n) can be synthetically controlled by adjusting the ratio between the spacer cation and the small organic cation, thus allowing the isolation of compounds in pure form and large scale. The orthorhombic crystal structures of (CH3(CH2)3NH3)2(CH3NH3)Pb2I7 (n = 2, Cc2m; a = 8.9470(4), b = 39.347(2) A, c = 8.8589(6)), (CH3(CH2)3NH3)2(CH3NH3)2Pb3I10 (...

http://pubs.acs.org/doi/pdf/10.1021/acs.chemmater.6b00847

Ruddlesden-Popper Hybrid Lead Iodide Perovskite 2D Homologous Semiconductors

An introductory review of various concepts about first-order phase transitions is given. Rules for classification of phase transitions as second or first order are discussed, as well as exceptions to these rules. Attention is drawn to the rounding of first-order transitions due to finite-size or quenched impurities. Computational methods to calculate phase diagrams for simple model Hamiltonians are also described. Particular emphasis is laid on metastable states near first-order phase transitions, on the 'stability limits' of such states (e.g. the 'spinodal curve' of the gas-liquid transition) and on the dynamic mechanisms by which metastable states decay (nucleation and growth of droplets of a new phase, etc.).

https://iopscience.iop.org/article/10.1088/0034-4885/50/7/001/pdf

Theory of first-order phase transitions

Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy. Growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering, x-ray diffraction, and reflection high energy electron diffraction. We observed at room temperature strong photoluminescence (PL) at 0.76 eV as well as a clear absorption edge at 0.7–1.0 eV. In contrast, no PL was observed, even by high power excitation, at ∼1.9 eV, which had been reported as the band gap in absorption experiments on polycrystalline films. Careful inspection strongly suggests that a wurtzite InN single crystal has a true bandgap of 0.7–1.0 eV, and the discrepancy could be attributed to the difference in crystallinity.

Optical bandgap energy of wurtzite InN

We study the influence of nitrogen, a potential acceptor in ZnO, on the lattice dynamics of ZnO. A series of samples grown by chemical vapor deposition (CVD) containing different nitrogen concentrations, as determined by secondary ion mass spectroscopy (SIMS), was investigated. The Raman spectra revealed vibrational modes at 275, 510, 582, 643, and 856 cm−1 in addition to the host phonons of ZnO. The intensity of these additional modes correlates linearly with the nitrogen concentration and can be used as a quantitative measure of nitrogen in ZnO. These modes are interpreted as local vibrational modes. Furthermore, SIMS showed a correlation between the concentration of incorporated nitrogen and unintentional hydrogen, similar to the incorporation of the p-dopant magnesium and hydrogen in GaN during metalorganic CVD.

/pdf/nitrogen-related-local-vibrational-modes-in-zno-n-h04ez87s1l.pdf

Nitrogen-related local vibrational modes in ZnO:N

We present the results of room- and low-temperature measurements of second-order Raman scattering for perfect GaN and AlN crystals as well as the Raman-scattering data for strongly disordered samples. A complete group-theory analysis of phonon symmetry throughout the Brillouin zone and symmetry behavior of phonon branches, including the analysis of critical points, has been performed. The combined treatment of these results and the lattice dynamical calculations based on the phenomenological interatomic potential model allowed us to obtain the reliable data on the phonon dispersion curves and phonon density-of-states functions in bulk GaN and AlN. @S0163-1829~98!06840-4#

/pdf/phonon-dispersion-and-raman-scattering-in-hexagonal-gan-and-2txa73pwej.pdf

Phonon dispersion and Raman scattering in hexagonal GaN and AlN

We determined the possible symmetries for band (Bloch) states at various points of the Brillouin zone. The spin–orbit interaction has been taken into account. Free excitons offer larger sets of possible state symmetries than single carriers do. The selection rules for the optical transitions have been established. Experiments with polarized light are shown to be relevant to study the nature (s or p) of A, B, and C excitons.

Optical Selection Rules for Hexagonal GaN

The phonon symmetry of a series of Aurivillius compounds ${[{\mathrm{Bi}}_{2}{\mathrm{O}}_{2}]}^{2+}$${[{A}_{n\ensuremath{-}1}{B}_{n}{\mathrm{O}}_{3n+1}]}^{2\ensuremath{-}}$ is studied by a site symmetry analysis of bulk crystals followed by the consecutive analysis of their common structural subunits, i.e., the metal-oxygen octahedra $B{\mathrm{O}}_{6}$ and individual layers. The division of the bulk crystals into rigid units $(B{\mathrm{O}}_{6})$ allowed to distinguish in the bulk phonon spectra the rigid unit modes involving the rotations of $B{\mathrm{O}}_{6}$ octahedra, which may be responsible for phase transitions from the tetragonal to intermediate phases. The symmetries of the rigid unit modes were found to vary in different Aurivillius compounds leading to different transition schemes within the Aurivillius family. The division of crystals into separate layers revealed the existence of Davydov doublets and quartets in the bulk spectra originating from the the same layer modes that considerably facilitates their symmetry assignment in Raman and infrared spectra. The group-theory predictions are in a good agreement with the ab initio calculations and experimental data that supports the validity of the single layer approach.

Site symmetry approach to phase transitions in perovskite-related ferroelectric compounds

We have investigated the optical spectra of different halogen-fullerene compounds: C60I42x ,C 70I2 ,C 60Br24, C60Cl24, and C70Cl17. Two types of carbon-halogen bonding have been established: ~a! C60I42x and C70I2 compounds are formed by a C60 or C70 molecule sublattice and an I2 molecule sublattice that weakly interact via van der Waals forces; ~b! C60Br24 ,C 60Cl24, and C70Cl17 compounds are characterized by covalent bonds between C and Br/Cl atoms. We have studied in detail the resonance effects in C60Cl24 using the methods of Raman scattering, infrared absorption, and absorption in the visible region. The effect originates from the interactions between the phonon subsystem and the electron band at 2.33 eV and manifests itself in a resonant enhancement of the Raman line intensities and in the repetition of the phonon and the luminescence spectra shifted by the frequency of Raman-active phonon at 1508 cm 21 . The group-theory analysis of phonon symmetries in rigid and nonrigid C60Br24 and C60Cl24 crystals has been performed. @S0163-1829~98!04710-9#

Yu. E. Kitaev

Papers

Phonon dispersion and Raman scattering in hexagonal GaN and AlN

Optical Selection Rules for Hexagonal GaN

Site symmetry approach to phase transitions in perovskite-related ferroelectric compounds

Phonons and electron-phonon interaction in halogen-fullerene compounds

Phonon spectrum of wurtzite GaN and AlN: Experiment and theory