The impact of a relaxed InGaN pseudosubstrate on indium incorporation in a full InGaN heterostructure was investigated. Three types of InGaN pseudosubstrates were tested with different a lattice parameters ranging from 3.190 to 3.205 Å, that is to say, greater than that of a GaN template on sapphire. Samples were loaded together in the growth chamber in order to apply exactly the same growth conditions. The effect of the photoluminescence (PL) emission redshift was observed on InyGa1-yN buffer layers and also on InxGa1-xN/InyGa1-yN multiple quantum wells (MQWs). It was found that these pseudosubstrates have the ability to improve the indium incorporation rate, with an increasing effect as the a lattice parameter increases. A strong PL emission redshift was observed in InxGa1-xN/InyGa1-yN MQWs as a function of the increasing a lattice parameter of the InGaN pseudosubstrate, compared to a reference grown on a GaN template. It has been shown that green and amber emissions can be easily reached. A redshift of up to 42 nm was detected between various InGaN pseudosubstrate samples and up to 62 nm compared to a conventional structure emerged from a GaN buffer on the sapphire substrate. The average QW width less than 3 nm indicates a higher In content. The reduced compressive strain originating from the relaxed InGaN substrate allows the reduction in the compositional pulling effect and consequently enables an enhanced In incorporation rate.

Controlling the polarity of ZnO nanowires in addition to the uniformity of their structural morphology in terms of position, vertical alignment, length, diameter, and period is still a technological and fundamental challenge for real-world device integration. In order to tackle this issue, we specifically combine the selective area growth on prepatterned polar c-plane ZnO single crystals using electron-beam lithography, with the chemical bath deposition. The formation of ZnO nanowires with a highly controlled structural morphology and a high optical quality is demonstrated over large surface areas on both polar c-plane ZnO single crystals. Importantly, the polarity of ZnO nanowires can be switched from O- to Zn-polar, depending on the polarity of prepatterned ZnO single crystals. This indicates that no fundamental limitations prevent ZnO nanowires from being O- or Zn-polar. In contrast to their catalyst-free growth by vapor-phase deposition techniques, the possibility to control the polarity of ZnO nanowires grown in solution is remarkable, further showing the strong interest in the chemical bath deposition and hydrothermal techniques. The single O- and Zn-polar ZnO nanowires additionally exhibit distinctive cathodoluminescence spectra. To a broader extent, these findings open the way to the ultimate fabrication of well-organized heterostructures made from ZnO nanowires, which can act as building blocks in a large number of electronic, optoelectronic, and photovoltaic devices.

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3 pagesInternational audienc

This letter reports the observation of the Purcell effect for CdSe∕ZnSe quantum dots located in a hybrid micropillar. The sample consist of a λ∕2-ZnSe cavity sandwiched between two SiO2∕TiO2 Bragg reflectors. Time-resolved photoluminescence (PL) measurements on a series of single-quantum dots were used to probe the Purcell effect in a 1.1μm diameter pillar. A three-fold enhancement of quantum-dot spontaneous emission rate is observed for quantum dots in resonance with excited degenerated modes of the pillar. The variation of the PL decay shortening from dot to dot is interpreted calculating the theoretical maximal Purcell factor for the different modes resonant with the dots.

Articles you may be interested inAtomic scale investigations on CdxZn1−xSe quantum dots: Correlation between the composition and emission properties Appl. Phys. Lett. 105, 053103 (2014); 10.1063/1.4891635 II-VI quantum dot formation induced by surface energy change of a strained layer

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