Single-crystal layers of AlN have been grown on sapphire substrates between 1000 and 1100 °C by vapor-phase reaction of aluminum chlorides with ammonia. The purity, color, crystallinity, growth morphology, and electrical resistivity of the epitaxial layers have been investigated. Infrared specular reflection measurements showed the presence of an appreciable strain at the AIN-sapphire epitaxy interface. Optical absorption data strongly suggest the AlN is a direct band-gap material with a value of about 6.2 eV at room temperature.

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A useful closed-form expression for stresses within individual layers of a multilayer composite has been obtained as a function of position within the layer. Equal and isotropic elastic constants were assumed in the calculation, although the error introduced by this assumption is found to vary by no more than the difference in elastic constants. Unequal elastic constants may be handled via computer solutions. The stresses within heterojunction AlxGa1−xAs/GaAs lasers are calculated as an example of the technique. The addition of Al to the active GaAs region is shown to have a drastic effect upon the active-region stress, changing it from tension to compression. This change of sign in stress is correlated with improvements in operating lifetimes of lasers.

Photoemission and secondary-emission measurements were made from AlxGa1−xAs (x=0, 0.1, 0.2, and 0.3) surfaces which were activated to negative electron affinity (NEA) using Cs and O2. Values for the diffusion length L and the surface escape factor B were determined from the data for each alloy composition. It was found that B decreases with increasing AlAs composition and that the diffusion lengths for all the alloys examined were at least 6.0 μm.

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