An overview is presented of the current state-of-the-art in silicon nanophotonic ring resonators. Basic theory of ring resonators is discussed, and applied to the peculiarities of submicron silicon photonic wire waveguides: the small dimensions and tight bend radii, sensitivity to perturbations and the boundary conditions of the fabrication processes. Theory is compared to quantitative measurements. Finally, several of the more promising applications of silicon ring resonators are discussed: filters and optical delay lines, label-free biosensors, and active rings for efficient modulators and even light sources.

/pdf/silicon-microring-resonators-3fzr4lpxbh.pdf

Silicon microring resonators

Plasmonic nanostructures hold promise for the realization of ultra-thin sub-wavelength devices, reducing power operating thresholds and enabling nonlinear optical functionality in metasurfaces. However, this promise is substantially undercut by absorption introduced by resistive losses, causing the metasurface community to turn away from plasmonics in favour of alternative material platforms (e.g., dielectrics) that provide weaker field enhancement, but more tolerable losses. Here, we report a plasmonic metasurface with a quality-factor (Q-factor) of 2340 in the telecommunication C band by exploiting surface lattice resonances (SLRs), exceeding the record by an order of magnitude. Additionally, we show that SLRs retain many of the same benefits as localized plasmonic resonances, such as field enhancement and strong confinement of light along the metal surface. Our results demonstrate that SLRs provide an exciting and unexplored method to tailor incident light fields, and could pave the way to flexible wavelength-scale devices for any optical resonating application.

/pdf/ultra-high-q-resonances-in-plasmonic-metasurfaces-1m7u472g4a.pdf

Ultra-high-Q resonances in plasmonic metasurfaces.

GaN and AlGaN have shown great potential in next-generation high-power electronic devices; however, they are plagued by a high density of interface states that affect device reliability and performance, resulting in large leakage current and current collapse. In this review, the authors summarize the current understanding of the gate leakage current and current collapse mechanisms, where awareness of the surface defects is the key to controlling and improving device performance. With this in mind, they present the current research on surface states on GaN and AlGaN and interface states on GaN and AlGaN-based heterostructures. Since GaN and AlGaN are polar materials, both are characterized by a large bound polarization charge on the order of 1013 charges/cm2 that requires compensation. The key is therefore to control the compensation charge such that the electronic states do not serve as electron traps or affect device performance and reliability. Band alignment modeling and measurement can help to determi...

Electronic surface and dielectric interface states on GaN and AlGaN

Ultra-high-Q resonances in plasmonic metasurfaces

Semiconductor science and technology (S T) is a very active branch in the field of natural science, and is also a typical example embodying the development of advanced S T. The Nobel prize for physics is a prize of the highest honour in the world, and there are certain relationships between this award and semiconductor S T. We explore and analyze these inherent relationships which have practical importance for our understanding of the development of semiconductor S T and for predicting its future.

Semiconductor science and technology, and Nobel physics prizes

A method is developed for extracting the coupling and loss coefficients of ring resonators from the peak widths, depths, and spacings of the resonances of a single resonator. Although the formulas used do not distinguish which coefficient is coupling and which is loss, it is shown how these coefficients can be disentangled based on how they vary with wavelength or device parameters.

Extracting coupling and loss coefficients from a ring resonator

Single-mode laser diodes on GaSb substrates were developed using InGaAsSb/AlGaAsSb triple quantum well active regions grown by molecular beam epitaxy. The devices were fabricated using lateral Cr gratings, with a grating pitch designed to coincide with a strong absorption feature of HF gas, deposited adjacent to a dry-etched narrow ridge waveguide. High sidemode suppression was achieved, and in 20 °C continuous-wave operation, devices with a 400 μm long cavity provided 9 mW total output power at the 2396 nm target wavelength. High-resolution direct absorption measurements of HF gas agreed with HiTran calculations, yielding an absorption linewidth of 0.030 nm.

Single-mode 2.4 μm InGaAsSb/AlGaAsSb distributed feedback lasers for gas sensing

High-resolution spectroscopy was used to examine gain characteristics of Cr-grating complex-coupled distributed-feedback (DFB) lasers near 2.4 $\mu$ m. The single-mode lasers contain InGaAsSb–AlGaAsSb active regions grown by molecular beam epitaxy on GaSb. Modal gain was extracted from the measured amplified spontaneous emission spectra and compared with reference Fabry–PErot lasers. The material gain is similar in both cases, having a value near 1300 cm $^{-1}$ , while the internal losses are quite different. The DFBs have an additional loss, approximately equal to the lateral Cr grating coupling coefficient. This indicates a fundamental performance limitation for complex-coupled DFBs.

Modal Gain of 2.4- $\mu$ m InGaAsSb–AlGaAsSb Complex-Coupled Distributed-Feedback Lasers

Single-mode laser diodes on GaSb substrates were developed using InGaAsSb/AlGaAsSb triple quantum well
active regions grown by molecular beam epitaxy. The devices were fabricated 
using lateral Cr gratings, with a grating pitch designed to coincide with a strong absorption feature of HF gas, deposited adjacent to a dry-etched narrow ridge waveguide.
High sidemode suppression was achieved, and in 20°C continuous-wave operation, devices with a 400μm-long cavity provided 4.5mW total output power
at the 2396nm target wavelength.
Anti-reflection and high-reflection facet coatings exhibited no deleterious effects on the laser tunability or mode quality, thus allowing
the preferential extraction of output power from a single laser facet.

Single-mode 2.4μm InGaAsSb/AlGaAsSb distributed feedback lasers for gas sensing

Current collapse is a limiting factor in the performance of AlGaN/GaN high electron mobility transistors (HEMTs), and can be ameliorated by silicon nitride passivation. The effect of three types of surface cleaning prior to the application of a silicon nitride passivation layer was studied. The best results were obtained when the wafers were cleaned using an air plasma descum followed by an HCl dip prior to the deposition of the silicon nitride passivation. Auger electron spectroscopy depth profiling indicated that the degree of collapse was correlated with the amount of residual carbon contamination at the silicon nitride/AlGaN interface.

The Effect of Surface Cleaning on Current Collapse in AlGaN ∕ GaN HEMTs

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