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In this study, molecular beam epitaxially grown axially configured ensemble GaAsSb/GaAs separate absorption, charge, and multiplication (SACM) region-based nanowire avalanche photodetector device on non-patterned Si substrate is presented. Our device exhibits a low breakdown voltage ( V BR ) of ∼ −10 ± 2.5 V under dark, photocurrent gain ( M ) varying from 20 in linear mode to avalanche gain of 700 at V BR at a 1.064 μm wavelength. Positive temperature dependence of breakdown voltage ∼ 12.6 mV K −1 further affirms avalanche breakdown as the gain mechanism in our SACM NW APDs. Capacitance–voltage ( C – V ) and temperature-dependent noise characteristics also validated punch-through voltage ascertained from I – V measurements, and avalanche being the dominant gain mechanism in the APDs. The ensemble SACM NW APD device demonstrated a broad spectral room temperature response with a cut-off wavelength of ∼1.2 μm with a responsivity of ∼0.17–0.38 A W −1 at −3 V. This work offers a potential pathway toward realizing tunable nanowire-based avalanche photodetectors compatible with traditional Si technology. 

Readability criteria, such as distance or neighborhood preservation, are often used to optimize node-link representations of graphs to enable the comprehension of the underlying data. With few exceptions, graph drawing algorithms typically optimize one such criterion, usually at the expense of others. We propose a layout approach, Graph Drawing via Gradient Descent, (GD)^2, that can handle multiple readability criteria. (GD)^2 can optimize any criterion that can be described by a smooth function. If the criterion cannot be captured by a smooth function, a non-smooth function for the criterion is combined with another smooth function, or auto-differentiation tools are used for the optimization. Our approach is flexible and can be used to optimize several criteria that have already been considered earlier (e.g., obtaining ideal edge lengths, stress, neighborhood preservation) as well as other criteria which have not yet been explicitly optimized in such fashion (e.g., vertex resolution, angular resolution, aspect ratio). We provide quantitative and qualitative evidence of the effectiveness of (GD)^2 with experimental data and a functional prototype: http://hdc.cs.arizona.edu/~mwli/graph-drawing/ 

Stress, edge crossings, and crossing angles play an important role in the quality and readability of graph drawings. Most standard graph drawing algorithms optimize one of these criteria which may lead to layouts that are deficient in other criteria. We introduce an optimization framework, Stress-Plus-X (SPX), that simultaneously optimizes stress together with several other criteria: edge crossings, minimum cross- ing angle, and upwardness (for directed acyclic graphs). SPX achieves results that are close to the state-of-the-art algorithms that optimize these metrics individually. SPX is flexible and extensible and can optimize a subset or all of these criteria simultaneously. Our experimental analysis shows that our joint optimization approach is successful in drawing graphs with good performance across readability criteria.