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The strain-compensation (SC) technique to reduce the accumulation of strain is a promising approach to increase the design flexibility as well as the performance of quantum dot (QD) lasers. Here we have studied the application of tensile-strained ultra-thin GaP layers into multiple stacked InAs/GaAs QD grown by MBE. XRD analysis shows the controllability of the average strain in multiple-stacked QD active layer, revealing a reduction in accumulated strain. Fabricated QD laser diodes including thinner QD active layers realized by SC technology show a narrower vertical far-field angle and an increased small signal modulation bandwidth without loss of gain. Cross-sectional SEM image of SC-QD LD active region

We present a novel structure of GaAsP nano apertures realized by employing the in situ thermal diffusion of phosphorus during epitaxial growth on top of quantum dot layers. Such structures may have direct device-oriented applications for the selective injection of electrical current into the dots. AFM and cross-sectional SEM images reveal that we are able to create elongated apertures in a diffusion layer of GaAsP by introducing a phosphorus flux during the growth, and that the apertures naturally form directly above the underlying dots. We also find that these nanoscale apertures are formed only when the distance between the top of the quantum dots and the diffusion layer is small enough, indicating that the aperture formation is due to the local strain field induced by the dots themselves. Schematic illustration of InAs/GaAs quantum dot layers and GaAsP nano-apertures.

A cell-based three-node triangular flat shell element with a bubble node is introduced to analyze frequencies of plates and shells. By smoothing the in-plane strains on sub-triangular domains created by connecting the bubble node to element nodes and applying the divergence theorem to derivatives in the gradient matrices, the integration of corresponding stiffness matrices are transformed from surface to line integrals. To remove the shear locking, the MITC3+ technique for three-node triangular degenerated shell elements with a bubble node is employed. The Craig-Bampton (CB) and enhanced Craig-Bampton (ECB) methods, which are well-known reduced-order modeling techniques based on substructuring strategy, are used for efficiently solving frequency analyses. Numerical results demonstrate the reliability and superiority of the present element, called CS-MITC3+, when combined with the substructuring methods to compute frequencies of plate and shell structures.

We fabricated a two dimensional photonic crystal nanocavity embedding a spatially-isolated active region containing InAs quantum dots using crystal regrowth with molecular beam epitaxy. We observed a cavity mode with a quality factor over 10,000, despite the existence of a mound structure on top of the buried active region due to faceting during the regrowth.

As VLSI technology scales to deep sub-micron, design for interconnections becomes increasingly challenging. The traditional bus routing follows a sequential bit-by-bit order, and few works explicitly target inter-bit regularity for signal groups via multi-layer topology selection. To overcome these limitations, we present Streak, an efficient framework that combines topology generation and wire synthesis with a global view of optimization and constrained metal layer track resource allocation. In the framework, an identification stage decomposes binding groups into a set of representative objects; with the generated backbones, equivalent topologies are accompanied by the bits in every object; then a formulation guides the routing considering wire congestion and design regularity. Experimental results using industrial benchmarks demonstrate the effectiveness of the proposed technique.

We report on high speed InAs/GaAs quantum dot lasers at 1.3 µm range. Small signal modulation response measurement for fabricated ridge laser exhibited record high maximum 3 dB bandwidth of 13.1 and 8.8 GHz at 25 and 85°C, respectively as 1.3 µm-range QD lasers. We adopted higher QD density not only to increase differential gain but also to reduce the barrier thickness in between QD layers to 30 nm. A higher QD density enables to minimize the local strain above QDs because of strain overlapping from neighboring dots, resulting in suppressing vertical alignment just above embed dot even with thinner barrier layer. This approach contributes to reduce carrier capture time in active region with increasing gain and differential gain in multiple-stacked QD active layers.

We demonstrate two dimensional photonic crystal nanocavities embedding spatially-isolated active regions containing InAs/GaAs self-assembled quantum dots. We fabricated the GaAs-based structures by a combination of electron-beam lithography, dry/wet etching and crystal regrowth using molecular beam epitaxy. The fabricated nanocavity based on a photonic crystal double heterostructure supports a cavity mode with a high experimental quality factor over 10,000, despite the existence of a mound structure on the nanocavity formed during the regrowth. Using electromagnetic simulations, we discuss the origin of the cavity mode and a direction for further increasing the quality factor. The two dimensional photonic crystal nanocavities with buried quantum dot active regions will provide a useful platform for developing high performance nanolasers.