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.

Avalanche multiplication and excess noise arising from both electron and hole injection have been measured on a series of In_0.52Al_0.48As p⁺-i-n⁺ and n ⁺-i-p⁺ diodes with nominal avalanche region widths between 0.1 and 2.5 mum. With pure electron injection, low excess noise was measured at values corresponding to effective k=beta/alpha between 0.15 and 0.25 for all widths. Enabled ionization coefficients were deduced using a non-local ionization model utilizing recurrence equation techniques covering an electric field range from approximately 200 kV/cm to 1 MV/cm

Simple analytical expressions for temperature coefficients of breakdown voltage of avalanche photodiodes (APDs) utilizing InP or InAlAs are reported. The work is based on measurements of temperature dependence of avalanche breakdown voltage in a series of InP and InAlAs diodes at temperatures between 20 and 375 K. While avalanche breakdown voltage becomes more temperature sensitive with avalanche region thickness for both materials, the InAlAs diodes are less sensitive to temperature changes compared to InP diodes.

We report excess noise factors measured on a series of InP diodes with varying avalanche region thickness, covering a wide electric field range from 180 to 850 kV/cm. The increased significance of dead space in diodes with thin avalanche region thickness decreases the excess noise. An excess noise factor of F = 3.5 at multiplication factor M = 10 was measured, the lowest value reported so far for InP. The electric field dependence of impact ionization coefficients and threshold energies in InP have been determined using a non-local model to take into account the dead space effects. This work suggests that further optimization of InP separate absorption multiplication avalanche photodiodes (SAM APDs) could result in a noise performance comparable to InAlAs SAM APDs.

A systematic study of avalanche multiplication on a series of In _0.52Al_0.48As p⁺-i-n⁺ and n ⁺-i-p⁺ diodes with nominal intrinsic region thicknesses ranging from 0.1 to 2.5 mum has been used to deduce effective ionization coefficients between 220 and 980 kVmiddotcm^-1. The electron and hole ionization coefficient ratio varies from 32.6 to 1.2 with increasing field. Tunneling begins to dominate the bulk current prior to avalanche breakdown in the 0.1-mum-thick structure, imposing an upper limit to the operating field. While the local model can accurately predict the breakdown in the diodes, multiplication is overestimated at low fields. The effects of ionization dead space, which becomes more significant as the intrinsic region thickness reduces, can be corrected for by using a simple correction technique

An experimental investigation into impact ionization in InAs photodiodes is presented. Photomultiplication measurements on p-i-n and n-i-p diodes show that while high avalanche gains can be obtained for electron initiated multiplication, there is virtually no gain with hole initiated multiplication. This indicates that the electron ionization coefficient is significantly greater than the hole ionization coefficient raising the possibility of extremely low noise InAs avalanche photodiodes when gain is initiated by electrons. The onset of electron initiated impact ionization was detectable at electric fields below 10kVcm−1 with useful gain observed at biases below 10V.