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Single-photon detection has emerged as a method of choice for ultra-sensitive measurements of picosecond optical transients. In the short-wave infrared, semiconductor-based single-photon detectors typically exhibit relatively poor performance compared with all-silicon devices operating at shorter wavelengths. Here we show a new generation of planar germanium-on-silicon (Ge-on-Si) single-photon avalanche diode (SPAD) detectors for short-wave infrared operation. This planar geometry has enabled a significant step-change in performance, demonstrating single-photon detection efficiency of 38% at 125 K at a wavelength of 1310 nm, and a fifty-fold improvement in noise equivalent power compared with optimised mesa geometry SPADs. In comparison with InGaAs/InP devices, Ge-on-Si SPADs exhibit considerably reduced afterpulsing effects. These results, utilising the inexpensive Ge-on-Si platform, provide a route towards large arrays of efficient, high data rate Ge-on-Si SPADs for use in eye-safe automotive LIDAR and future quantum technology applications. By incorporating germanium, single-photon avalanche diode detectors using silicon-based platforms are applied to infrared light detection. Here, a cost-effective planar detector geometry is presented yielding high detection efficiency suitable for applications such as sparse photon imaging or LIDAR.

Flash memories are essential for modern electronics; here a selenium-templated polyoxometalate is used to engineer new metal–oxide–semiconductor devices. Flash memory goes molecular Flash memory is becoming standard for smart phones, cameras, memory sticks and other devices. Its achievable data storage densities are ultimately limited by the minimum size of the individual data cells that can be fabricated, so molecule-based flash memory is an attractive proposition for stretching these limits. Christoph Busche and colleagues report the design, synthesis and electronic characterization of a family of metal-oxide cluster molecules that are compatible with current technology. The new materials are highly configurable at the atomic-level and show promise for implementation in practical devices. Flash memory devices—that is, non-volatile computer storage media that can be electrically erased and reprogrammed—are vital for portable electronics, but the scaling down of metal–oxide–semiconductor (MOS) flash memory to sizes of below ten nanometres per data cell presents challenges. Molecules have been proposed to replace MOS flash memory 1 , but they suffer from low electrical conductivity, high resistance, low device yield, and finite thermal stability, limiting their integration into current MOS technologies. Although great advances have been made in the pursuit of molecule-based flash memory 2 , there are a number of significant barriers to the realization of devices using conventional MOS technologies 3 , 4 , 5 , 6 , 7 . Here we show that core–shell polyoxometalate (POM) molecules 8 can act as candidate storage nodes for MOS flash memory. Realistic, industry-standard device simulations validate our approach at the nanometre scale, where the device performance is determined mainly by the number of molecules in the storage media and not by their position. To exploit the nature of the core–shell POM clusters, we show, at both the molecular and device level, that embedding [(Se( iv )O 3 ) 2 ] 4− as an oxidizable dopant in the cluster core allows the oxidation of the molecule to a [Se( v ) 2 O 6 ] 2− moiety containing a {Se( v )–Se( v )} bond (where curly brackets indicate a moiety, not a molecule) and reveals a new 5+ oxidation state for selenium. This new oxidation state can be observed at the device level, resulting in a new type of memory, which we call ‘write-once-erase’. Taken together, these results show that POMs have the potential to be used as a realistic nanoscale flash memory. Also, the configuration of the doped POM core may lead to new types of electrical behaviour 9 , 10 , 11 . This work suggests a route to the practical integration of configurable molecules in MOS technologies as the lithographic scales approach the molecular limit 12 .

The measurement of tiny variations in local gravity enables the observation of subterranean features. Gravimeters have historically been extremely expensive instruments, but usable gravity measurements have recently been conducted using MEMS (microelectromechanical systems) sensors. Such sensors are cheap to produce, since they rely on the same fabrication techniques used to produce mobile phone accelerometers. A significant challenge in the development of MEMS gravimeters is maintaining stability over long time periods, which is essential for long term monitoring applications. A standard way to demonstrate gravimeter stability and sensitivity is to measure the periodic elastic distortion of the Earth due to tidal forces—the Earth tides. Here, a 19 day measurement of the Earth tides, with a correlation coefficient to the theoretical signal of 0.975, has been presented. This result demonstrates that this MEMS gravimeter is capable of conducting long-term time-lapse gravimetry, a functionality essential for applications such as volcanology.

Gravimeters are used to measure density anomalies under the ground. They are applied in many different fields from volcanology to oil and gas exploration, but present commercial systems are costly and massive. A new type of gravity sensor has been developed that utilises the same fabrication methods as those used to make mobile phone accelerometers. In this study, we describe the first results of a field-portable microelectromechanical system (MEMS) gravimeter. The stability of the gravimeter is demonstrated through undertaking a multi-day measurement with a standard deviation of 5.58 × 10 − 6 ms − 2 . It is then demonstrated that a change in gravitational acceleration of 4.5 × 10 − 5 ms − 2 can be measured as the device is moved between the top and the bottom of a 20.7 m lift shaft with a signal-to-noise ratio (SNR) of 14.25. Finally, the device is demonstrated to be stable in a more harsh environment: a 4.5 × 10 − 4 ms − 2 gravity variation is measured between the top and bottom of a 275-m hill with an SNR of 15.88. These initial field-tests are an important step towards a chip-sized gravity sensor.

Junction-less nanowire transistors are being investigated to solve short channel effects in future CMOS technology. Here we demonstrate 8 nm diameter silicon nanowire junction-less transistors with metallic doping densities which demonstrate clear 1D electronic transport characteristics. The 1D regime allows excellent gate modulation with near ideal subthreshold slopes, on- to off-current ratios above 10 8 and high on-currents at room temperature. Universal conductance scaling as a function of voltage and temperature similar to previous reports of Luttinger liquids and Coulomb gap behaviour at low temperatures suggests that many body effects including electron-electron interactions are important in describing the electronic transport. This suggests that modelling of such nanowire devices will require 1D models which include many body interactions to accurately simulate the electronic transport to optimise the technology but also suggest that 1D effects could be used to enhance future transistor performance.

The development of three-dimensional architectures in semiconductor technology is paving the way to new device concepts for various applications, from quantum computing to single photon avalanche detectors. In most cases, such structures are achievable only under far-from-equilibrium growth conditions. Controlling the shape and morphology of the growing structures, to meet the strict requirements for an application, is far more complex than in close-to-equilibrium cases. The development of predictive simulation tools can be essential to guide the experiments. A versatile phase-field model for kinetic crystal growth is presented and applied to the prototypical case of Ge/Si vertical microcrystals grown on deeply patterned Si substrates. These structures, under development for innovative optoelectronic applications, are characterized by a complex three-dimensional set of facets essentially driven by facet competition. First, the parameters describing the kinetics on the surface of Si and Ge are fitted on a small set of experimental results. To this goal, Si vertical microcrystals have been grown, while for Ge the fitting parameters have been obtained from data from the literature. Once calibrated, the predictive capabilities of the model are demonstrated and exploited for investigating new pattern geometries and crystal morphologies, offering a guideline for the design of new 3D heterostructures. The reported methodology is intended to be a general approach for investigating faceted growth under far-from-equilibrium conditions.

Migrant workers typically commence the migration process as healthy individuals. However, diverse circumstances throughout migration cycle may render them highly vulnerable to poor physical and mental health outcome. This Perspective explores current data, global health policies regarding health of migrant workers, and roles travel health providers can play.

Germanium‐containing short‐wave infrared (SWIR) avalanche photodiode (APD) arrays on silicon platforms have the potential for monolithic integration into complementary metal‐oxide‐semiconductor (CMOS) integrated circuits, making them mass‐manufacturable, high‐performance, arrayed optical detectors operating at wavelengths beyond the silicon cut‐off wavelength. Here, the first high‐performance, surface‐illuminated, 10‐pixel linear array of pseudoplanar geometry germanium‐on‐silicon (Ge‐on‐Si) APDs operating at 1550 nm wavelength and at temperatures up to 378 K are demonstrated. At room temperature, the dark current, avalanche gain, responsivity, and avalanche breakdown of the devices show good uniformity. Array A exhibits a mean dark current density of 198 ± 62 mA cm−2 at 90% of the breakdown voltage. The excess noise factor is less than half that of InP‐based SWIR APD arrays, which allows Ge‐on‐Si devices to operate at a higher avalanche gain. A responsivity of 8.2 A W−1 at a gain of 20 and excess noise of 3.3 is achieved when illuminated with 1550 nm wavelength light. The detector array also demonstrates stable performance at 378 K with a maximum avalanche gain of 24. This device architecture will be applicable for the design of large‐scale APD arrays on Si platforms for SWIR detection which can be used in imaging, sensing, and optical communication applications. The fabrication and characterization of a new type of surface‐illuminated Si‐based avalanche photodiode array operating in the short‐wave infrared region using germanium as the absorber and silicon as the multiplier is reported. The demonstration of an avalanche gain of 24 at a temperature of 378 K allows the devices to operate in outdoor environments.

Nanoantennas: Concentrated infrared light source for molecular analysisA nanoantenna resonant in the mid-infrared frequency range demonstrates promise for optical devices that analyze molecules. Mid-infrared frequency light can be used to detect molecular vibrations, enabling detailed analyses of individual molecules at the quantum level, which is useful for medical and environmental applications. Previous plasmonic nanoantennas developed to concentrate such light and drive nonlinear processes were not effective at Mid-infrared wavelengths. Now, Daniele Brida and co-workers have built a plasmonic nanoantenna using highly-doped germanium grown on silicon substrates, which acts as an ultrafast, tunable nonlinear light source when it is excited by a laser. Their nanoantenna is capable of third harmonic generation – the creation of a light wave with a tripled frequency (one third of the original wavelength) - allowing for enhanced interaction of light and molecules in the Mid-infrared.

A microelectromechanical system (MEMS) gravimeter has been manufactured with a sensitivity of 40 ppb in an integration time of 1 s. This sensor has been used to measure the Earth tides: the elastic deformation of the globe due to tidal forces. No such measurement has been demonstrated before now with a MEMS gravimeter. Since this measurement, the gravimeter has been miniaturized and tested in the field. Measurements of the free-air and Bouguer effects have been demonstrated by monitoring the change in gravitational acceleration measured while going up and down a lift shaft of 20.7 m, and up and down a local hill of 275 m. These tests demonstrate that the device has the potential to be a useful field-portable instrument. The development of an even smaller device is underway, with a total package size similar to that of a smartphone. This article is part of a discussion meeting issue ‘The promises of gravitational-wave astronomy’.