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
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%.
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