The use of a high-growth-temperature $\mathrm{GaAs}$ spacer layer is demonstrated to significantly improve the performance of $1.3\mu \mathrm{m}$ multilayer self-assembled $\mathrm{InAs}∕\mathrm{InGaAs}$ dot-in-a-well lasers. The high-growth-temperature spacer layer inhibits threading dislocation formation, resulting in enhanced electrical and optical characteristics. Incorporation of these spacer layers allows the fabrication of multilayer quantum-dot devices emitting above $1.3\mu \mathrm{m}$ , with extremely low room-temperature threshold current densities and with operation up to $105°\mathrm{C}$ .

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.

This paper describes the design, fabrication, and performance of planar-geometry InGaAs-InP devices which were specifically developed for single-photon detection at a wavelength of 1550 nm. General performance issues such as dark count rate, single-photon detection efficiency, afterpulsing, and jitter are described.

Photomultiplication measurements using 244- and 325-nm excitation have been undertaken on a series of thick 4H-SiC avalanche diodes. With avalanche widths of between 2.7 and 6 mum and the ability to measure multiplication as low as 1.001, a much wider electric field range has been covered than reported to date. The results show that the hole ionization coefficient (beta) can be obtained with a high degree of accuracy down to electric fields as low as ~0.9 MV/cm. The value of electron ionization coefficient (alpha) has been determined from mixed carrier multiplication characteristics, and the beta/alpha ratio is found to increase significantly with decreasing electric fields. Ionization coefficients are parameterized over the electric field range from 0.9 to 5 MV/cm, enabling the multiplication and breakdown characteristics of 4H-SiC to be predicted accurately.

It is demonstrated that the emission of InAs quantum dots (QDs) capped with GaAsSb can be extended from 1.28to1.6μm by increasing the Sb composition of the capping layer from 14% to 26%. Photoluminescence excitation spectroscopy is applied to investigate the nature of this large redshift. The dominant mechanism is shown to be the formation of a type-II transition between an electron state in the InAs QDs and a hole state in the GaAsSb capping layer. The prospects for using these structures to fabricate 1.55μm injection lasers are discussed.