We report the high-frequency modulation of individual pixels in 8 × 8 arrays of III-nitride-based micro-pixellated light-emitting diodes, where the pixels within the array range from 14 to 84 μ m in diameter. The peak emission wavelengths of the devices are 370, 405, 450 and 520 nm, respectively. Smaller area micro-LED pixels generally exhibit higher modulation bandwidths than their larger area counterparts, which is attributed to their ability to be driven at higher current densities. The highest optical -3 dB modulation bandwidths from these devices are shown to be in excess of 400 MHz, which, to our knowledge, are the highest bandwidths yet reported for GaN LEDs. These devices are also integrated with a complementary metal-oxide-semiconductor (CMOS) driver array chip, allowing for simple computer control of individual micro-LED pixels. The bandwidth of the integrated micro-LED/CMOS pixels is shown to be up to 185 MHz; data transmission at bit rates up to 512 Mbit/s is demonstrated using on-off keying non return-to-zero modulation with a bit-error ratio of less than 1 × 10^-10, using a 450 nm-emitting 24 μm diameter CMOS-controlled micro-LED. As the CMOS chip allows for up to 16 independent data inputs, this device demonstrates the potential for multi-Gigabit/s parallel data transmission using CMOS-controlled micro-LEDs.

Single-photon detectors with picosecond timing resolution have advanced rapidly in the past decade. This has spurred progress in time-correlated single-photon counting applications, from quantum optics to life sciences and remote sensing. A variety of advanced optoelectronic device architectures offer not only high-performance single-pixel devices but also the ability to scale up to detector arrays and extend single-photon sensitivity into the short-wave infrared and beyond. The advent of single-photon focal plane arrays is poised to revolutionize infrared imaging and sensing. In this mini-review, we set out performance metrics for single-photon detection, assess the requirements of single-photon light detection and ranging, and survey the state of the art and prospects for new developments across semiconductor and superconducting single-photon detection technologies. Our goal is to capture a snapshot of a rapidly developing landscape of photonic technology and forecast future trends and opportunities.

A 256 x 256 single-photon avalanche diode (SPAD) sensor integrated into a 3-D-stacked 90-nm 1P4M/40-nm 1P8M process is reported for flash light detection and ranging (LIDAR) or high-speed direct time-of-flight (ToF) 3-D imaging. The sensor bottom tier is composed of a 64 x 64 matrix of 36.72-μm pitch modular photon processing units which operate from shared 4 x 4 SPADs at 9.18-μm pitch and 51% fill-factor. A 16 x 14 bit counter array integrates photon counts or events to compress data to 31.4 Mb/s at 30-frame/s readout over 8 I/O operating at 100 MHz. The pixel-parallel multi-event time-to-digital converter (TDC) approach employs a programmable internal or external clock for 0.56-560-ns time bin resolution. In conjunction with a per-pixel correlator, the power is reduced to less than 100 mW in practical daylight ranging scenarios. Examples of ranging and high-speed 3-D ToF applications are given.

An 8 × 16 pixel array based on CMOS small-area silicon photomultipliers (mini-SiPMs) detectors for PET applications is reported. Each pixel is 570 × 610 μm² in size and contains four digital mini-SiPMs, for a total of 720 SPADs, resulting in a full chip fill-factor of 35.7%. For each gamma detection, the pixel provides the total detected energy and a timestamp, obtained through two 7-b counters and two 12-b 64-ps TDCs. An adder tree overlaid on top of the pixel array sums the sensor total counts at up to 100 Msamples/s, which are then used for detecting the asynchronous gamma events on-chip, while also being output in real-time. Characterization of gamma detection performance with an 3 × 3 × 5 mm³ LYSO scintillator at 20°C is reported, showing a 511-keV gamma energy resolution of 10.9% and a coincidence timing resolution of 399 ps.

A single-photon avalanche diode structure implemented in a 130-nm imaging process is reported. The device employs a p-well anode, rather than the commonly adopted p+, and a novel guard ring compatible with recent scaling trends in standard nanometer scale complementary metal-oxide-semiconductor technologies. The 50-mum ² active area device exhibits a dark count rate of 25 Hz at 20 ^degC and a photon detection efficiency peak of 28% at 500 nm.

A 192 x 128 pixel single photon avalanche diode (SPAD) time-resolved single photon counting (TCSPC) image sensor is implemented in STMicroelectronics 40-nm CMOS technology. The 13% fill factor, 18.4 μm x 9.2 μm pixel contains a 33-ps resolution, 135-ns full scale, 12-bit time-to-digital converter (TDC) with 0.9-LSB differential and 5.64-LSB integral nonlinearity (DNL/INL). The sensor achieves a mean 219-ps full-width half-maximum (FWHM) impulse response function (IRF) and is operable at up to 18.6 kframes/s through 64 parallelized serial outputs. Cylindrical microlenses with a concentration factor of 3.25 increase the fill factor to 42%. The median dark count rate (DCR) is 25 Hz at 1.5-V excess bias. A digital calibration scheme integrated into a column of the imager allows off-chip digital process, voltage, and temperature (PVT) compensation of every frame on the fly. Fluorescence lifetime imaging microscopy (FLIM) results are presented.