Spontaneous Polarization Calculations in Wurtzite II-Oxides, III-Nitrides, and SiC Polytypes through Net Dipole Moments and the Effects of Nanoscale Layering

Herein, the spontaneous polarization in crystals with hexagonal symmetry are calculated as a function of the number of monolayers composing a nanostructure by adding the dipole moments for consecutive units of the nanostructure. It is shown that in the limit of a large numbers of monolayers that the spontaneous polarization saturates to the expected bulk value of the spontaneous polarization. These results are relevant to understanding the role of the built-in spontaneous polarizations in a variety of nanostructures since these built-in polarizations are generally quite large, on the order of 1 × 108 to 1 × 1010 V/m. Using these formulations, we come to the prediction that small nanolayered structures are theoretically capable of having larger spontaneous polarizations than their bulk counterparts due to how the dipole moments of the anions and cations within a wurtzite lattice cancel out with one another more in larger structures.

Cadmium sulfide / selenide pigments

Cadmium sulfide and selenide pigments (cadmium pigments) belong to the inorganic yellow, orange and red pigments. Cadmium sulfide pigments are based on the wurtzite lattice, where cadmium can be partially substituted by zinc or mercury and sulfide by selenide. Cadmium pigments are characterized by excellent optical and application characteristics in particular regarding brightness of shade, hiding power, tinting strength, and weather fastness. The declining use of cadmium-containing materials in the last decades is a result of the environmental discussion and the development of less problematic substitute products, especially of bismuth vanadate and high-value organic, temperature-stable yellow and red pigments.

Alloys and Exotic Materials

The chapter describes how the band parameters of ternary and quaternary alloys can be interpolated over the entire range of compositions, and tabulate the non-vanishing bowing parameters for most of the common alloys with both zinc-blende and wurtzite lattice structure. It also describes ordering in some of the ternary alloys, and how ordering affects the energy gap. The band parameters of dilute nitrides, dilute bismides, and hexagonal boron nitride are also examined. Finally, the chapter presents schemes for interpolating the optical parameters of III–V alloys, i.e., the real and imaginary parts of the permittivity or dielectric function.

Growth of ZnO Microstructure on Porous Silicon

In this study, Zinc Oxide (ZnO) microstructures were grown on porous silicon (PS) using chemical bath deposition (CBD) method by varying the growth time. The field emission scanning electron microscopy (FESEM) revealed the morphology and sized of ZnO. The X-ray diffraction (XRD) spectra indicate the high quality growth of ZnO on PS surface. Raman analyses revealed the peaks shift of E2(High), characterized wurtzite lattice and indicates good crystallinity of ZnO.

The growth, structure and luminescence properties of ZnSe1-xSx materials

ZnSe1-xSxcrystals with a higher content of selenium or sulfur ions adopt, respectively, a wurtzite or sphalerite structure. Luminescent properties of ZnSe1-xSxcrystals are determined by ternary VZnZniOSecomplexes for crystals with a cubic (sphalerite) lattice, and by sulfur vacancies VSfor crystals with a hexagonal (wurtzite) lattice. Light output of ZnSe1-xSxcrystals increases with increasing the sulfur content up tox= 0.3 and reaches the value of light output observed for ‘classic scintillator’ ZnSe(Te). At the same time, the ZnSe1-xSxbulk crystals possess better thermal stability at the same energy of emitted photons (hν~ 2 eV) as compared to that of the ZnSe(Te) crystals.

Epitaxial Growth and Structural Characterization of Single Crystalline ZnGeN2

A new nitride semiconductor, single crystalline ZnGeN2 has been successfully grown by MOCVD for the first time. The epitaxial ZnGeN2 is found to be of hexagonal wurtzite lattice without ordering of the zinc and germanium atoms in the pseudomorphic Group III sublattice. Lattice constants of the ZnGeN2 are a = 3.186 ± 0.007 A, c = 5.174 ± 0.012 A, which gives c/a = 1.624.

Epitaxial Growth and Structural Characterization of Single Crystalline ZnGeN2

A new nitride semiconductor, single crystalline ZnGeN2 has been successfully grown by MOCVD for the first time. The epitaxial ZnGeN2 is found to be of hexagonal wurtzite lattice without ordering of the zinc and germanium atoms in the pseudomorphic Group III sublattice. Lattice constants of the ZnGeN2 are a = 3.186 ± 0.007 A, c = 5.174 ± 0.012 A, which gives c/a = 1.624.

Pinholes, Dislocations and Strain Relaxation in InGaN

We analyse by means of transmission electron microscopy (TEM) and atomic force microscopy (AFM) the strain relaxation mechanisms in InGaN layers on GaN as dependent on the In content. At the experimentally given thickness of 100 nm, the layers remain coherently strained, up to an In concentration of 14 %. We show that part of the strain is reduced elastically by formation of hexagonally facetted pinholes. First misfit dislocations are observed to form at pinholes that reach the InGaN/GaN interface. We discuss these results in the framework of the Matthews-Blakeslee model for the critical thickness considering the Peierls force for glide of threading dislocations in the different slip systems of the wurtzite lattice.