Ultrafast Silicon Nanomembrane Microbolometer for Long-Wavelength Infrared Light Detection.

The microbolometer is the cornerstone device for imaging in the long-wavelength infrared range (LWIR) at room temperature. The state-of-the-art commercial microbolometers usually have a large thermal time constant (TTC) of over 10 ms, limited by their substantial device heat capacity. Moreover, the minimal pixel size of state-of-the-art bolometer is around 10 µm by 10 µm to ensure sufficient power absorption per pixel. Here, we demonstrate an ultrafast silicon nanomembrane microbolometer with a small heat capacity of around 1.9 × 10-11J/K, which allows for its operation at a speed of over 10 kHz, corresponding to a TTC of less than 16 µs. Moreover, a compact diabolo antenna is leveraged for efficient LWIR light absorption, enabling the downscaling of the active area size to 6.2 µm by 6.2 µm. Because of the complementary metal oxide semiconductor (CMOS)-compatible fabrication processes, our demonstration here may lead to a future high-resolution and high-speed LWIR imaging solution.

Vapor condensation with daytime radiative cooling.

A radiative vapor condenser sheds heat in the form of infrared radiation and cools itself to below the ambient air temperature to produce liquid water from vapor. This effect has been known for centuries, and is exploited by some insects to survive in dry deserts. Humans have also been using radiative condensation for dew collection. However, all existing radiative vapor condensers must operate during the nighttime. Here, we develop daytime radiative condensers that continue to operate 24 h a day. These daytime radiative condensers can produce water from vapor under direct sunlight, without active consumption of energy. Combined with traditional passive cooling via convection and conduction, radiative cooling can substantially increase the performance of passive vapor condensation, which can be used for passive water extraction and purification technologies.

Origami silicon optoelectronics for hemispherical electronic eye systems.

Digital image sensors in hemispherical geometries offer unique imaging advantages over their planar counterparts, such as wide field of view and low aberrations. Deforming miniature semiconductor-based sensors with high-spatial resolution into such format is challenging. Here we report a simple origami approach for fabricating single-crystalline silicon-based focal plane arrays and artificial compound eyes that have hemisphere-like structures. Convex isogonal polyhedral concepts allow certain combinations of polygons to fold into spherical formats. Using each polygon block as a sensor pixel, the silicon-based devices are shaped into maps of truncated icosahedron and fabricated on flexible sheets and further folded either into a concave or convex hemisphere. These two electronic eye prototypes represent simple and low-cost methods as well as flexible optimization parameters in terms of pixel density and design. Results demonstrated in this work combined with miniature size and simplicity of the design establish practical technology for integration with conventional electronic devices.

Silicon single-photon avalanche diodes with nano-structured light trapping.

Silicon single-photon avalanche detectors are becoming increasingly significant in research and in practical applications due to their high signal-to-noise ratio, complementary metal oxide semiconductor compatibility, room temperature operation, and cost-effectiveness. However, there is a trade-off in current silicon single-photon avalanche detectors, especially in the near infrared regime. Thick-junction devices have decent photon detection efficiency but poor timing jitter, while thin-junction devices have good timing jitter but poor efficiency. Here, we demonstrate a light-trapping, thin-junction Si single-photon avalanche diode that breaks this trade-off, by diffracting the incident photons into the horizontal waveguide mode, thus significantly increasing the absorption length. The photon detection efficiency has a 2.5-fold improvement in the near infrared regime, while the timing jitter remains 25 ps. The result provides a practical and complementary metal oxide semiconductor compatible method to improve the performance of single-photon avalanche detectors, image sensor arrays, and silicon photomultipliers over a broad spectral range.The performance of silicon single-photon avalanche detectors is currently limited by the trade-off between photon detection efficiency and timing jitter. Here, the authors demonstrate how a CMOS-compatible, nanostructured, thin junction structure can make use of tailored light trapping to break this trade-off.

Single-crystalline germanium nanomembrane photodetectors on foreign nanocavities.

Miniaturization of optoelectronic devices offers tremendous performance gain. As the volume of photoactive material decreases, optoelectronic performance improves, including the operation speed, the signal-to-noise ratio, and the internal quantum efficiency. Over the past decades, researchers have managed to reduce the volume of photoactive materials in solar cells and photodetectors by orders of magnitude. However, two issues arise when one continues to thin down the photoactive layers to the nanometer scale (for example, <50 nm). First, light-matter interaction becomes weak, resulting in incomplete photon absorption and low quantum efficiency. Second, it is difficult to obtain ultrathin materials with single-crystalline quality. We introduce a method to overcome these two challenges simultaneously. It uses conventional bulk semiconductor wafers, such as Si, Ge, and GaAs, to realize single-crystalline films on foreign substrates that are designed for enhanced light-matter interaction. We use a high-yield and high-throughput method to demonstrate nanometer-thin photodetectors with significantly enhanced light absorption based on nanocavity interference mechanism. These single-crystalline nanomembrane photodetectors also exhibit unique optoelectronic properties, such as the strong field effect and spectral selectivity.