Crystalline zinc blende GaAs has been grown on a trigonal c-plane sapphire substrate by molecular beam epitaxy. The initial stage of GaAs thin film growth has been investigated extensively in this paper. When grown on c-plane sapphire, it takes (111) crystal orientation with twinning as a major problem. Direct growth of GaAs on sapphire results in three-dimensional GaAs islands, almost 50% twin volume, and a weak in-plane correlation with the substrate. Introducing a thin AlAs nucleation layer results in complete wetting of the substrate, better in-plane correlation with the substrate, and reduced twinning to 16%. Further, we investigated the effect of growth temperature, pregrowth sapphire substrate surface treatment, and in-situ annealing on the quality of the GaAs epilayer. We have been able to reduce the twin volume below 2% and an X-ray diffraction rocking curve line width to 223 arcsec. A good quality GaAs on sapphire can result in the implementation of microwave photonic functionality on a photonic chip.
DécouvrirThe new method of making mixed halide-perovskites results in solar cells with improved stability and performance. The new method results in better control over perovskite crystallization rates.
Lire la suiteIn 1900, German physician Paul Ehrlich came up with the notion of a “magic bullet.” The basic idea is to inject a patient with smart particles capable of finding, recognizing, and treating a disease. Medicine has pursued the magic bullet ever since.
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