Showing papers on "Wurtzite crystal structure published in 1973"

Raman Spectrum of Wurtzite Silicon

Abstract: The Raman spectrum of a metastable polycrystalline sample of wurtzite silicon is reported. The data are analyzed using a large-zone comparison with the diamond cubic phase of silicon and in terms of a simple force-constant model. These measurements are compared with the Raman spectrum of amorphous silicon and with the microcrystallite model of the amorphous phase.

On the structure of amorphous germanium and silicon

Abstract: The simple microcrystallite model is used to calculate the diffraction and radial distribution functions for a variety of tetrahedrally coordinated crystal structures: diamond, wurtzite, Ge III and Si III — two high-pressure polytypes of Ge and Si — and two clathrate structures based on pentagonal dodecahedral units. Comparison with data for sputtered amorphous Ge suggests that the simple microcrystallite model is inadequate to fit diffraction data. A statistical or combination microcrystallite model may be more promising. Recent electron microscopic investigations of Rudee and Howie are also discussed.

Static Equilibrium Conditions for a Rigid-Ion Crystal

Abstract: The equilibrium requirements for a static ionic crystal impose a number of constraints on the short-range forces which become increasingly more important when one is dealing with complex structures. These constraints are presented and discussed for a general rigid-ion lattice, and a specific discussion is presented for the wurtzite structure.

EPR Spectra of Transition Element Impurities with 3d2 Configuration in Hexagonal CdS and CdSe Single Crystals

Abstract: Electron paramagnetic resonance has been studied for divalent titanium with 3d2 configuration substituting for Cd in hexagonal single crystals of cadmium sulphide and cadmium selenide. The parameters of the spin-Hamiltonian have been determined at T = 27 and 77 K. It is found that the symmetry of the centre is axial, corresponding to the C3V symmetry of an isolated impurity on normal lattice sites in wurtzite. Elektronenparamagnetische Resonanz wurde an zweiwertigem Titan mit 3d2-Konfiguration, das Cd substituiert, in hexagonalen Einkristallen von Kadmiumsulfid und Kadmiumselenid untersucht. Die Parameter des Spin-Hamiltonoperators wurden bei T = 27 und 77 K. bestimmt. Es wird gefunden, das die Symmetrie der Zentren axial ist, entsprechend der C3V-Symmetrie einer isolierten Storstelle auf normalem Gitterplatz in Wurtzit.

Electronic charge densities for ZnS in the wurtzite and zincblende structures

Abstract: Using the Empirical Pseudopotential Method electronic charge densities are calculated as a function of position in the unit cell for ZnS in a zincblende and ideal wurtzite structure. A comparison of the charge densities reveals the presence of a net polarization in the ideal wurtzite structure. Two representative k points are found whose total charge density is in very good agreement with the charge density obtained by summing over many points in the irreducible part of the Brillouin zone.

Effective Ionic Charges of Several Uniaxial Crystals

Abstract: A simple equation was derived for obtaining the effective ionic charges of uniaxial crystals on the basis of a rigid ion model by using the optically active lattice vibration frequencies of the TO and LO modes. It was applied to several uniaxial crystals such as wurtzite type (ZnO, ZnS, CdS, and BeO) and rutile type (ZnF2, TiO2, SnO2, and GeO2) crystals. Lattice vibration frequencies of orthorhombic hydrogen chloride crystal were calculated by means of a point charge model to estimate the effect of the long range Coulomb interaction on the vibrational frequencies of molecular crystals.

Epitaxial growth and structure of CdS films evaporated onto Ge

Abstract: CdS evaporated in vacuum grew epitaxially at all substrate temperatures from 300 to 500° C on (100), (110) and (111) surfaces of germanium. On (100) substrates the CdS grew with the sphalerite structure in parallel orientation to the substrate. Films grown throughout the epitaxial range of temperature gave diffraction patterns that contained no satellite spots. They all contained 〈111〉 streaking, however. The films were therefore free of threedimensional defects but contained a high density of {111} planar defects. On the (110) substrates the CdS grew with the sphalerite structure in parallel orientation for substrate temperatures below about 370° C and the diffraction patterns of these films were free of satellite spots but contained 〈111〉 streaks of low intensity. In the diffraction patterns of the films grown above about 370° C doubling of the spots appeared and a domain structure was observed in the micrographs. This was due to the occurrence of a domain-form phase transformation of the sphalerite structure. On the (111) substrates the CdS grew with the wurtzite structure in (0001) orientation. No satellite spots or streaks appeared in the diffraction patterns of these films. Moire fringes were seen in the micrographs of both (100) and (111) substrate specimens.

Internal Strain in Zincblende and Wurtzite Crystals

Abstract: A new method of calculating the bond-bending parameter from experimental elastic properties is presented. The values obtained are used to analyze the piezoelectric constant, and a simple relationship between dipole and quadrupole contributions is found. The results are also applied to the equilibrium wurtzite structure for which the built-in internal strain is predicted for a number of relevant crystals. Eine neue Methode zur Berechnung des „bond-bending” Parameters aus experimentellen elastischen Eigenschaften wird beschrieben. Die berechneten Werte werden fur die Analyse der piezo-elektrischen Konstanten verwendet. und eine einfache Relation zwischen den Dipol- und Quadrupol-Beitragen wird gefunden. Die Ergebnisse werden auch fur die Gleichgewichts-Wurtzitstruktur verwendet, und in diesem Fall wird die spontane innere Deformation fur wichtige Kristalle vorausgesagt.