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A systematic investigation on the effects of growth temperature, Ga flux, and Sb flux on the incorporation of Sb, film structure, and optical properties of the GaN1-xSbx highly mismatched alloys (HMAs) was carried out. We found that the direct bandgap ranging from 3.4 eV to below 1.0 eV for the alloys grown at low temperature. At the growth temperature of 80 °C, GaN1-xSbx with x > 6% losses crystallinity and becomes primarily amorphous with small crystallites of 2-5 nm. Despite the range of microstructures found for GaN1-xSbx alloys with different composition, a well-developed absorption edge shifts from 3.4 eV (GaN) to close to 2 eV for samples with a small amount, less than 10% of Sb. Luminescence from dilute GaN1-xSbx alloys grown at high temperature and the bandgap energy for alloys with higher Sb content are consistent with a localized substitutional Sb level ESb at ~1.1 eV above the valence band of GaN. The decrease in the bandgap of GaN1-xSbx HMAs is consistent with the formation of a Sb-derived band due to the anticrossing interaction of the Sb states with the valence band of GaN. [ABSTRACT FROM AUTHOR]

Recent developments with group III nitrides suggest AlxGa1-xN based LEDs can be new alternative commercially viable deep ultra-violet light sources. Due to a significant difference in the lattice parameters of GaN and AlN, AlxGa1-xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1-xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE) using a novel RF plasma source. Thick wurtz-ite AlxGa1-xN films were grown by PA-MBE on 2-inch GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1-xN samples. Growth rates of AlxGa1-xN up to 3 µm/h have been demonstrated. Our novel high efficiency RF plasma source allowed us to achieve free-standing bulk AlxGa1-xN layers in a single day's growth, which makes our MBE bulk growth technique commercially viable. [ABSTRACT FROM AUTHOR]

In this letter, we study the optical properties of GaN1-xSbx thin films. Films with an Sb fraction up to 42% were synthesized by alternating GaN-GaSb layers at a constant temperature of 325 °C. The measured optical absorption data of the films are interpreted using a modified band anticrossing model that is applicable to highly mismatched alloys such as GaN1-xSbx in the entire composition range. The presented model allows us to more accurately determine the band gap as well as the band edges over the entire composition range thereby providing means for determining the composition for, e.g., efficient spontaneous photoelectrochemical cell applications. [ABSTRACT FROM AUTHOR]

Two In x Ga 1-x N nanorod samples with graded In compositions of x = 0.5-0 (Ga-rich) and x = 0.5-1 (In-rich) grown by molecular beam epitaxy were studied using transmission electron microscopy. The nanorods had a wurtzite crystal structure with growth along [Formula: see text] and core-shell structures with an In-rich core and Ga-rich shell. Energy-dispersive x-ray analysis confirmed grading over the entire compositional range and showed that the axial growth rate was primarily determined by the In flux, and the radial growth rate by the Ga flux. There was no evidence of misfit dislocations due to grading, but the strain due to the lattice mismatch between the In-rich core and Ga-rich shell was relaxed by edge dislocations at the core-shell interface with Burgers vectors [Formula: see text] and [Formula: see text].

GaN 1-x Sb x with x∼5%-7% is a highly mismatched alloy predicted to have favorable properties for application as an electrode in a photoelectrochemical cell for solar water splitting. In this study, we grew GaN 1-x Sb x under conditions intended to induce phase segregation. Prior experiments with the similar alloy GaN 1-x As x , the tendency of Sb to surfact, and the low growth temperatures needed to incorporate Sb all suggested that GaN 1-x Sb x alloys would likely exhibit phase segregation. We found that, except for very high Sb compositions, this was not the case and that instead interdiffusion dominated. Characteristics measured by optical absorption were similar to intentionally grown bulk alloys for the same composition. Furthermore, the alloys produced by this method maintained crystallinity for very high Sb compositions and allowed higher overall Sb compositions. This method may allow higher temperature growth while still achieving needed Sb compositions for solar water splitting applications.