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Al x Ga 1−x N alloys were grown on c-plane sapphire by plasma-induced molecular beam epitaxy. The Al content x was varied over the whole composition range (0⩽x⩽1). The molar Al fraction was deduced from x-ray diffraction and for comparison by elastic recoil detection analysis. The composition of the alloys calculated from the lattice parameter c underestimates x. This is due to a deformation of the unit cell. The exact Al mole fraction and the biaxial strain of the alloys can be calculated by an additional determination of a, using asymmetric reflections. The results obtained by x-ray diffraction and elastic recoil detection provide evidence for the validity of Vegard’s law in the AlGaN system. In addition, the deviation of the band gap from a linear dependence on x was investigated. We found a downward bowing with a bowing parameter b=1.3 eV.

To determine the sound velocity in wurtzite AlxGa1−xN, we have used surface acoustic-wave (SAW) delay lines on AlxGa1−xN/c-Al2O3. AlxGa1−xN films with compositions from x=0 to x=1 were grown by plasma-induced molecular beam epitaxy. Starting from published data, we fine tuned the values of the elastic moduli used in numerical calculations such that the simulated and measured dispersion of the SAW were in good agreement. Based on these values, the surface and bulk acoustic-wave velocities of single-crystal AlxGa1−xN were determined as functions of the composition. The resulting SAW velocities ranged from 3700 to 5760 m/s for GaN and AlN, respectively.

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Abstract:The synthesis and properties of [Ga(N,),], (1) and the related derivatives [(Do),Ga(N,),] (2a-d: Do = THF, NEt,, NMe,, quinuclidine, n = 1; 2e: Do = pyridine; n = 3

gas-phase precursor reaction, have been reported. ["] In our experiments, relatively high substrate temperatures were chosen (600-650 "C) to accommodate the higher decomposition temperature of the other precursors. These results indicated that, although the films were depleted in Ce, empirical relationships may be established to allow control of deposit composition by the solution composition. Such relationships are very complex, however, and much more experimental work will be needed before definitive predictive relationships can be given.For use as practical 02-selective membranes, CVD deposits such as the one depicted in Figure 3 must be defect free, in addition to possessing desirable oxygen transport properties. The oxygen transport properties may be characterized by conductivity measurements or by direct oxygen permeation measurements at high temperature. The membrane layer must be essentially leak (defect) free before meaningful oxygen permeation measurements can be done. The doped, stabilized ZrOz membranes fabricated thus far have had rather high leakage rates. We believe this is partially due to the relatively large pore size and nonuniform surface of the porous substrates, which may make complete pore blockage difficult to achieve. Unfortunately, there are very limited choices for porous supports available commercially. We are therefore investigating support surface modifications to make the surface more planar and reduce the pore size, as well as investigating reducedpressure deposition more closely.In summary, CeOz-doped Y203.stabilized Zr02 films have been deposited onto porous substrates at atmospheric and reduced pressures by AACVD using a single precursor solution of metal tmhd precursors. Single-phase CeOzdoped stabilized cubic ZrOz was obtained as-deposited over a range of compositions. Reduced-pressure deposition (-10 torr) resulted in a more uniform deposit morphology, and lower C incorporation due to higher relative 0 2 content in the vapor mixture. Preliminary characterization indicates that the deposit and precursor solution compositions differ, but that empirical relationships between solution and film compositions can be employed to control the composition of the deposit. Leak-tight layers for membrane applications have not yet been produced. This is a challenging task requiring good control of the support structure, as well as the CVD process. In general, AACVD is a useful technique for deposition of multicomponent metal oxide films, particularly when precursors with poor volatility or thermal stability are involved.The group-I11 nitrides AlN, GaN, and InN are candidates for applications as light-emitting diodes and semiconductor lasers operating at short wavelengths of the optical spectrum. These materials have several advantages, including direct bandgaps for high efficiency in optoelectronic devices, high radiation hardness, and complete solubility among the binary compounds. Hexagonal CaN is of particular interest because of its potential as a wide-bandgap (3.45 eV) electroluminesc...