Thermal annealing effect on InAs/InGaAs quantum dots grown by atomic layer molecular beam epitaxy

The effect of rapid thermal annealing on the InAs quantum dots (QDs) grown by atomic layer molecular beam epitaxy and capped with InGaAs layer has been investigated using transmission electron microscopy and photoluminescence (PL). Different from the previously reported results, no obvious blueshift of the PL emission of QDs is observed until the annealing temperature increases up to 800 degreesC. The size and shape of the QDs annealed at 750 degreesC have hardly changed indicating the relatively weak Ga/In interdiffusion, which is characterized by little blueshift of the PL peak of QDs. The QD size increases largely and a few large clusters can be observed after 800 degreesC RTA, implying the fast interdiffusion and the formation of InGaAs QDs. These results indicate that the delay of the blueshift of the PL peak of QDs is correlated with the abnormal interdiffusion process, which can be explained by two possible reasons: the reduction of excess-As-induced defects and the redistribution of In, Ga atoms around the InAs QDs resulted from the sub-monolayer deposition of InGaAs capping layer. (C) 2004 Elsevier B.V. All rights reserved.

Surface morphology of AlN buffer layer and its effect on GaN growth by metalorganic chemical vapor deposition

The in situ optical reflectivity measurements are employed to monitor the GaN epilayer growth process above low-temperature AlN buffer layer on c-plane sapphire substrate by metalorganic chemical vapor deposition. It is found that the lateral growth of GaN islands and their coalescence is promoted in the initial growth stage if the AlN buffer layer is treated with a long annealing time and has an optimal thickness: As confirmed by atomic force microscopy observations, the quality of GaN epilayers is closely dependent on the surface morphology of AlN buffer layer, especially the grain size and nuclei density after the annealing treatment. (C) 2004 American Institute of Physics.

The influence of AlN buffer layer thickness on the properties of GaN epilayer

The influence of low-temperature AlN buffer layer thickness on GaN epilayer was investigated by triple-axis X-ray diffraction (XRD) and photoluminescence measurements. A method was proposed to measure the screw and edge dislocation densities by XRD. It was found that the buffer layer thickness was a key parameter to affect the quality of GaN epilayer and an appropriate thickness resulted in the best structural and optical properties except the lateral grain size. After the thickness exceeding the appropriate value, the compressive stress in the epilayer decreased as the thickness increased, which led to the redshift of the near-band edge luminescence. The experimental results showed the buffer layer thickness had more influence on edge dislocation than screw type and the former was perhaps the main source of the yellow band. (C) 2004 Elsevier B.V. All rights reserved.

Effect of In0.2Ga0.8As and In0.2Al0.8As combination layer on band offsets of InAs quantum dots

We demonstrate the self-organized InAs quantum dots capped with thin and In0.2Al0.8As and In0.2Ga0.8As combination layers with a large ground and first excited energy separation emission at 1.35 mum at room temperature. Deep level transient spectroscopy is used to obtain quantitative information on emission activation energies and capture barriers for electrons and holes. For this system, the emission activation energies are larger than those for InAs/GaAs quantum dots. With the properties of wide energy separation and deep emission activation energies, self-organized InAs quantum dots capped with In0.2Al0.8As and In0.2Ga0.8As combination layers are one of the promising epitaxial structures of 1.3 mum quantum dot devices. (C) 2004 American Institute of Physics.

Single-mode behaviour judgment of optical waveguides by imaginary-distance beam propagation method under perfectly matched layer boundary condition

Imaginary-distance beam propagation method under the perfectly matched layer boundary condition is applied to judge single-mode behaviour of optical waveguides, for the first time to our knowledge. A new kind of silicon-on-insulator-based rib structures with half-circle cross-section is presented. The single-mode behaviour of this kind of waveguide with radius 2mum is investigated by this method. It is single-mode when the slab height is not smaller than the radius.