Nitride-based structures

One of the most basic properties of the optical gain in nitride-based structures is its polarisation dependence. In contrast to other bulk III-V materials, where the optical gain is isotropic, nitride structures exhibit almost exclusively TE-mode gain [14]. This is due to the symmetry-induced splitting of the valence bands in the wurtzite structure. 

Nitrides can be sub-divided into ionic, covalent and interstitial types.An alternate general classification of nitrides, based on bonding classification, as ionic, covalent and metallic has also been applied. Ionic or salt-like nitrides are formed by electropositive elements such as Li, Mg, Ca, Sr, Ba, Cu, Zn, Cd and Hg and possess formulae which correspond to those expected on the basis of the combination of the metal ion with ions. A range of covalent nitrides are known and are exhibited by less electropositive elements such as B, S, P, C and Si. Interstitial nitrides are formed by some transition metals and refer to compounds which can be described in terms of the occupancy of interstitial sites in close packed metallic structures by nitrogen atoms. Oxygen can also be accommodated within these structures and a range of oxynitrides are known to... 

Optical pumping experiments were first used to achieve lasing m GaN-based structures. Stimulated emission from GaN was observed as early as 1971 [17]. More recently, there have been a large number of reports on stimulated emission [18,19], without an intentionally formed cavity. This may partly be due to the well known difficulty of cleaving mirrors in the wurtzite nitrides grown on sapphire, due to the 30° tilt of the GaN unit cell with respect to the sapphire. 

Both injection-type and optically pumped nitride-based semiconductor laser structures exhibit fairly high threshold pump levels compared to other III-V or II-VI semiconductors. This is fundamentally due to the specific band structure of the nitrides, i.e. the extremely large effective masses of both electrons and holes. The carrier densities needed to achieve transparency are of the order 2 x 1019 cm 3. 

Ternary phases with structures different from those of the phases of the binary boundary systems are more the exception than the rule. Such phases have been reported in the systems Nb-Mo-N, Ta-Mo-N, Nb-Ta-N, Zr-V-N, Nb-Cr-N, and Ta-Cr-N. Information about ternary transition metal-nitrogen systems is often available for specific temperatmes only. This is even more the case for quaternary nitride systems, which play a role in the production of carbonitride cermets where quaternary compounds of the types (Ti,Mo)(C,N) and (Ti,W)(C,N) are of interest (see Carbides Transition Metal Solid-state Chemistry), as well as in layer technology where titanium nitride-based coatings of the type Ti(C,B,N) are prepared by magnetron sputtering. Layers consisting of ternary compounds of the type (Ti,Al)N and (Ti,V)N also have favorable properties with respect to abrasion resistance. 

Since their mechanical properties are maintained at high temperatures (up to 1700 K), silicon nitride-based materials are attractive for use in high-temperature structural applications in chemically aggressive environments. For example, several properties of a Si3N4-based ceramic (Si3N4-l-SiC+TiN), suitable for ceramic engines, are shown in Table Vm. 

The application of HP results in improved structural properties of the nitride-based SOI structures. The HP-induced effects in Si N are related to the changed diffusivity of nitrogen and the misfit at the SiN /Si matrix boundary as well as to different number of nucleation sites for formation of amorphous and crystalline phases, in particular, N2-filled nanobubles. 

Figure 1 shows the two models which were calculated. The base structure was considered with another research group for improvement of the thermal conductivity, while three layered structure was adopted on the view point of shielding. The base structure was assumed to be a concentric cylinder of 60 cm height which was formed void, strontium titanate ( "SrTiOs, P 5.12g/cm 0 and boron nitride (BN, p 2.26g/cm3) from the inside. The weight of these two materials was made to be identical each other. 

Recently, blue lasers have been developed in strained layer II-VI structures [41], An example of a blue laser structure is shown in Figure 4-37. An example of a blue laser structure is shown in Figure 4-37. Several additional research groups have now produced blue lasers in a variety of configurations [42, 43], including a nitride based one by Nichia. 

Silicon nitride-based polycrystalline ceramic materials have the potential for structural applications at both room temperature and elevated temperatures, despite containing silicate/silicate-rich oxynitride grain boundary phases. These are generally much weaker compared to the silicon nitride single crystal grains of which the... 

Li, Y.Q. (2005) Structural and Imninescence properties of novel rare-earth doped silicon nitride based materials. Ph.D. Thesis, Technical University of Eindhoven. 

Wilding MC, Wilson M, McMiUan PF (2006) Structural studies and polymorphism in amorphous solids and liquids at high pressure. Chem Soc Rev 35 964-986 Horvath-Bordon E, Riedel R, Zerr A et al (2006) High-pressure chemistry of nitride-based materials. Chem Soc Rev 35 987-1014... 

A class of variants of the ceramics related to alumina is based on the ternary Al-O-N system, which forms 13 different compounds, some of which are polyt)rpes of aluminium nitride based on the wurtzite structure. 

Like carbon, boron nitride forms structures such as nanotubes, nanomeshes, and BN-based fullerenes. 

This is the first book devoted to the theoretical modelling of refractory carbides and nitrides and alloys based on them. It makes use of computational methods to calculate their spectroscopic, electric, magnetic, superconducting, thermodynamical and mechanical properties. Calculated results on the electronic band structure of ideal binary transition-metal carbides and nitrides are presented, and the influences of crystal lattice defects, vacancies and impurities are studied in detail. Data available on chemical bonding and the properties of multi-component carbide- and nitride-based alloys, as well as their surface electronic structure, are described, and compared with those of bulk crystals. 

STRUCTURE AND PROPERTIES OP SILICON AND TITATIUM NITRIDES-BASE MATERIALS... 

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