We examine the current performance and future demands of interconnects to and on silicon chips. We compare electrical and optical interconnects and project the requirements for optoelectronic and optical devices if optics is to solve the major problems of interconnects for future high-performance silicon chips. Optics has potential benefits in interconnect density, energy, and timing. The necessity of low interconnect energy imposes low limits especially on the energy of the optical output devices, with a ~ 10 fJ/bit device energy target emerging. Some optical modulators and radical laser approaches may meet this requirement. Low (e.g., a few femtofarads or less) photodetector capacitance is important. Very compact wavelength splitters are essential for connecting the information to fibers. Dense waveguides are necessary on-chip or on boards for guided wave optical approaches, especially if very high clock rates or dense wavelength-division multiplexing (WDM) is to be avoided. Free-space optics potentially can handle the necessary bandwidths even without fast clocks or WDM. With such technology, however, optics may enable the continued scaling of interconnect capacity required by future chips.

Device Requirements for Optical Interconnects to Silicon Chips

The past decade has seen rapid progress in research into high-performance Ge-on-Si photodetectors. Owing to their excellent optoelectronic properties, which include high responsivity from visible to near-infrared wavelengths, high bandwidths and compatibility with silicon complementary metal–oxide–semiconductor circuits, these devices can be monolithically integrated with silicon-based read-out circuits for applications such as high-performance photonic data links and infrared imaging at low cost and low power consumption. This Review summarizes the major developments in Ge-on-Si photodetectors, including epitaxial growth and strain engineering, free-space and waveguide-integrated devices, as well as recent progress in Ge-on-Si avalanche photodetectors. Owing to their excellent optoelectronic properties, Ge-on-Si photodetector can be monolithically integrated with silicon-based read-out circuits for applications such as high-performance photonic data links and low-cost infrared imaging at low power consumption. This Review covers the major developments in Ge-on-Si photodetectors, including epitaxial growth and strain engineering, free-space and waveguide-integrated devices, as well as recent progress in Ge-on-Si avalanche photodetectors.

High-performance Ge-on-Si photodetectors

Industries such as the automotive, aerospace or military, as well as environmental and biological research have promoted the development of ultraviolet (UV) photodetectors capable of operating at high temperatures and in hostile environments. UV-enhanced Si photodiodes are hence giving way to a new generation of UV detectors fabricated from wide-bandgap semiconductors, such as SiC, diamond, III-nitrides, ZnS, ZnO, or ZnSe. This paper provides a general review of latest progresses in wide-bandgap semiconductor photodetectors.

https://iopscience.iop.org/article/10.1088/0268-1242/18/4/201/pdf

Wide-bandgap semiconductor ultraviolet photodetectors

We report the electrical and optical characteristics of avalanche photodiodes fabricated in GaN grown by metalorganic chemical vapor deposition. The current–voltage characteristics indicate a multiplication of >25. Experiment indicates and simulation verifies that the magnitude of the electric field at the onset of avalanche gain is ⩾3 MV/cm. Small-area devices exhibit stable gain with no evidence of microplasmas.

GaN avalanche photodiodes

A series of weaknesses in creativity, research design, and quality of writing continue to handicap energy social science. Many studies ask uninteresting research questions, make only marginal contributions, and lack innovative methods or application to theory. Many studies also have no explicit research design, lack rigor, or suffer from mangled structure and poor quality of writing. To help remedy these shortcomings, this Review offers suggestions for how to construct research questions; thoughtfully engage with concepts; state objectives; and appropriately select research methods. Then, the Review offers suggestions for enhancing theoretical, methodological, and empirical novelty. In terms of rigor, codes of practice are presented across seven method categories: experiments, literature reviews, data collection, data analysis, quantitative energy modeling, qualitative analysis, and case studies. We also recommend that researchers beware of hierarchies of evidence utilized in some disciplines, and that researchers place more emphasis on balance and appropriateness in research design. In terms of style, we offer tips regarding macro and microstructure and analysis, as well as coherent writing. Our hope is that this Review will inspire more interesting, robust, multi-method, comparative, interdisciplinary and impactful research that will accelerate the contribution that energy social science can make to both theory and practice.

Promoting novelty, rigor, and style in energy social science: towards codes of practice for appropriate methods and research design

In this paper, we study the mechanisms of the 4H-SiC avalanche photodiode (APD) dark current and find that the mesa sidewall leakage current is the primary contributor. Improving the sidewall passivation decreases the device dark current.

Low dark current 4H-SiC avalanche photodiodes

The detection of light in the UV portion of the electromagnetic spectrum is critical to a number of applications. Until very recently, the primary means of light detection in the UV was with either silicon photodiodes or photomultiplier tubes, both of which have serious drawbacks. With the advent of optoelectronic devices fabricated in the ternary alloy of AlGaN, the possibility exists to produce high-performance solid-state photodetector arrays sensitive to the visible-blind and solar-blind regions of the spectrum. In this paper, we discuss recent advances in the area of UV photodetectors fabricated on GaN and AlGaN. Various device structures are presented, and their peculiar characteristics discussed in terms of responsivity, dark current, gain, temporal response, and frequency response. Models describing the current transport mechanisms and the quantum efficiencies of these photodiodes are discussed. Special emphasis is given to novel device structures that improve on the temporal, spectral, and electrical characteristics of AlGaN-based photodiodes. Specifically, results for a transparent recessed-window p-i- n device, and a semi-transparent electrode device structure are described. Finally, the results of a separate absorption, charge, and multiplication avalanche photodetector are presented. This device structure resulted in a stable gain of > 10 at a reverse bias of approximately 40 V.

High-performance GaN/AlGaN-based ultraviolet photodetectors

18 Increasing urbanization puts ever-increasing pressure on cities to prioritize sustainable growth and avoid carbon lock-in, yet available modeling frameworks and tools fall acutely short of robustly guiding such pivotal decision-making at the local level. Financial incentives, behavioral interventions, and mandates 21 drive sustainable technology adoption, while land-use zoning plays a critical role in carbon emissions from the built environment. Researchers typically evaluate impacts of policies top down, on a national scale, or else post-hoc on developments vis-à-vis different polices in the past. Such high-level analyses 24 and post-hoc evaluations cannot forecast emission pathways for specific cities, and hence cannot serve as input to local policymakers. Here, we present IMPACT pathways, from a bottom-up model with residence level granularity, that integrate technology adoption policies with zoning policies, climate 27 change, and grid decarbonization scenarios. With the city at the heart of our analysis, we show that for our site rapid grid decarbonization is the largest single mitigation measure. We identify an emission premium for sprawling development and show that adverse policy combinations exist that can exhibit 30 rebounding emissions over time.

IMPACT: Integrated Multi-Domain Emission Pathways For Cities Under Land-Use Policy, Technology Adoption, Climate Change And Grid Decarbonization

Gallium phosphide, though most commonly used in emitters, has potential for use in both ultraviolet, blue, and blue green light detection applications from 250 nm to 500 nm. In GaP, shorter wavelengths have a higher absorption coefficient and consequently a shorter absorption length. Therefore, increased quantum efficiency in the UV spectrum hinges on these carriers reaching the active region prior to recombination. Thus, we implemented a recessed window structure to reduce the p-region thickness, resulting in increased quantum efficiency at shorter wavelengths. An improved peak quantum efficiency of 38% occurs at /spl sim/440 nm. It is also important to note the enhanced quantum efficiency at short wavelengths, especially those below the spectral range of the non-recessed devices.

UV/blue GaP avalanche photodiodes

We report separate absorption and multiplication 4H-SiC avalanche photodiodes. An external quantum efficiency of 83% (187 mA/W) at 278 nm corresponding to unity gain after reach-through was achieved. Gain higher than 1000 was demonstrated without edge breakdown

http://ieeexplore.ieee.org/iel5/10387/33016/01548034.pdf

Ariane L. Beck

Papers

Low dark current 4H-SiC avalanche photodiodes

High-performance GaN/AlGaN-based ultraviolet photodetectors

IMPACT: Integrated Multi-Domain Emission Pathways For Cities Under Land-Use Policy, Technology Adoption, Climate Change And Grid Decarbonization

UV/blue GaP avalanche photodiodes

Ultraviolet separate absorption and multiplication 4H-SiC avalanche photodiodes