Continued development of GaN-based light emitting diodes is being hampered by constraints imposed by current non-native substrates. ZnO is a promising alternative substrate but it decomposes under the conditions used in conventional GaN metal organic vapor phase epitaxy ͑MOVPE͒. In this work, GaN was grown on ZnO / c-Al 2 O 3 using low temperature/pressure MOVPE with N 2 as a carrier and dimethylhydrazine as a N source. Characterization confirmed the epitaxial growth of GaN. The GaN was lifted-off the c-Al 2 O 3 by chemically etching away the ZnO underlayer. This approach opens up the way for bonding of the GaN onto a support of choice.

We report on the growth, fabrication, and device characterization of AlGaN-based thin-film ultraviolet (UV) (k $ 359 nm) light emitting diodes (LEDs). First, AlN/Si(111) template is patterned. Then, a fully coalesced 7-lm-thick lateral epitaxial overgrowth (LEO) of AlN layer is realized on patterned AlN/Si(111) template followed by UV LED epi-regrowth. Metalorganic chemical vapor deposition is employed to optimize LEO AlN and UV LED epitaxy. Back-emission UV LEDs are fabricated and flip-chip bonded to AlN heat sinks followed by Si(111) substrate removal. A peak pulsed power and slope efficiency of $0.6 mW and $1.3 lW/mA are demonstrated from these thin-film UV LEDs, respectively. For comparison, top-emission UV LEDs are fabricated and back-emission LEDs are shown to extract 50% more light than top-emission ones. V

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Using elastic scattering theory we show that a small set of energy dispersive x-ray spectroscopy (EDX) measurements is sufficient to experimentally evaluate the scattering function of electrons in high-angle annular dark field scanning transmission microscopy (HAADF-STEM). We then demonstrate how to use this function to transform qualitative HAADF-STEM images of InGaN layers into precise, quantitative chemical maps of the indium composition. The maps obtained in this way combine the resolution of HAADF-STEM and the chemical precision of EDX. We illustrate the potential of such chemical maps by using them to investigate nanometer-scale fluctuations in the indium composition and their impact on the growth of epitaxial InGaN layers.

We report on the bandgap variation in thin films of B x Ga 1−x N grown on AlN/sapphire substrates using metal-organic vapor phase epitaxy. Optical transmission, photoluminescence, and x-ray diffraction were utilized to characterize the materials' properties of the B x Ga 1−x N films. In contrast to the common expectation for the bandgap variation, which is based on the linear interpolation between the corresponding GaN and BN values, a significant bowing ͑C = 9.2Ϯ 0.5 eV͒ of the bandgap was observed. A decrease in the optical bandgap by 150 meV with respect to that of GaN was measured for the increase in the boron composition from 0% to 1.8%.

International audienceIn this paper we report on a spontaneous 2D/3D transition observed in InGaN alloys after 60 nm of growth. This transition is responsible for the formation of a stack of distinct InGaN layers. The driving mechanism is shown to be lateral fluctuations of the indium composition, that arise to accommodate the increasing strain energy of the InGaN layer. Three distinct stages of growth have been identified. First, a homogeneous, 2D InGaN layer forms, pseudomorphically strained on the underlying GaN. Then, at around 30 nm large lateral fluctuations of the indium composition are observed and a second pseudomorphic layer, composed of indium-rich and indium-poor clusters, is formed. Finally induces a 2D/3D transition at 60 nm and a 3D InGaN layer is formed

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