Fast, sensitive avalanche photodiodes (APDs) are required for applications such as high-speed data communications and light detection and ranging (LIDAR) systems. Unfortunately the InP and InAlAs used at the gain material in these APDs have similar electron and hole impact ionisation coefficients (α and β respectively) at high electric fields, giving rise to relatively high excess noise, limiting their sensitivity and gain bandwidth product (GBP) 1. Here, we report on extremely low excess noise in AlAs0.56Sb0.44 lattice matched to InP. The deduced β/α ratio as low as 0.005 in the avalanche region of 1550 nm is close the theoretical minimum and is significantly smaller than Silicon, with modelling suggesting that vertically illuminated APDs with a sensitivity of-25.7 dBm at a bit-error rate (BER) of 1×10-12 at 25 Gb/s at 1550 nm can be realised. The findings could yield a new breed of high performance receivers for applications in networking and sensing. The advantages of using InP based APDs at traditional telecommunication wavelengths of 1310 nm and 1550 nm as a way of increasing sensitivity and speed of communication networks is well documented 2,3,4. Such APDs utilise InGaAs lattice matched to InP substrates as the absorber and an InP or InAlAs gain (or multiplication) region in the Separate Absorption and Multiplication (SAM)-APD configuration. However due to the broadly similar β/α ratio in these materials, particularly at high fields, their sensitivity and GBP are limited, hampering their use as the bit rate increases beyond 10 Gb/s. The best results at 25 Gb/s to 50 Gb/s currently utilise ≤ 100 nm thick InAlAs multiplication regions and these provide a sensitivity of between-22.6 dBm to-10 dBm respectively at a BER of 1×10-125-7. There have been many attempts at improving the performance of APDs for telecommunications, for example utilising Ge/Si 8-10 , nanopillars 11 , AlInAsSb 12-14 or InAs 15 , however these face problems such as limited wavelength operation, often requiring difficult growth procedures, complex fabrication technologies or the use of more expensive substrates. In this letter we demonstrate that the InP lattice matched alloy system AlAs0.56Sb0.44 with its very small β/α ratio 16 leads to extremely low excess noise at room temperature, even at high gains, exceeding the performance of all materials lattice matched to InP and even silicon. This extremely small β/α ratio changes the paradigm whereby high speed APDs always use very thin avalanching structures to one where both high speed and sensitivity can be achieved with thicker avalanching structures. Three AlAs0.56Sb0.44 structures with avalanche region thicknesses of 1550 nm (P1), 660 nm (P2) and 1150 nm (P3) in a PIN configuration and two NIP structures with avalanche region thicknesses of 1550 nm (N1) and 660 nm (N2) were investigated. Fig. 1a shows a schematic diagram of P1 with

Light detection and ranging (LiDAR) sensors enable precision sensing of an object in 3D. LiDAR technology is widely used in metrology, environment monitoring, archaeology, and robotics. It also shows high potential to be applied in autonomous driving. In traditional LiDAR sensors, mechanical rotator is used for optical beam scanning, which brings about limitations on their reliability, size, and cost. These limitations can be overcome by a more compact solid‐state solution. Solid‐state LiDAR sensors are commonly categorized into the following three types: flash‐based LiDAR, microelectromechanical system (MEMS)‐based LiDAR, and optical phased array (OPA)‐based LiDAR. Furthermore, advanced optics technology enables novel nanophotonics‐based devices with high potential and superior advantages to be utilized in a LiDAR sensor. In this review, LiDAR sensor principles are introduced, including three commonly used sensing schemes: pulsed time of flight (TOF), amplitude‐modulated continuous wave TOF, and frequency‐modulated continuous wave. Recent advances in conventional solid‐state LiDAR sensors are summarized and presented, including flash‐based LiDAR, MEMS‐based LiDAR, and OPA‐based LiDAR. The recent progress on emerging nanophotonics‐based LiDAR sensors is also covered. A summary is made and the future outlook on advanced LiDAR sensors is provided.

The electron and hole avalanche multiplication characteristics have been measured in bulk AlAs0.56Sb0.44 p-i-n and n-i-p homojunction diodes, lattice matched to InP, with nominal avalanche region thicknesses of ~0.6 μm, 1.0 μm and 1.5 μm. From these and data from two much thinner devices, the bulk electron and hole impact ionization coefficients (α and β respectively), have been determined over an electric-field range from 220–1250 kV/cm for α and from 360–1250 kV/cm for β for the first time. The α/β ratio is found to vary from 1000 to 2 over this field range, making it the first report of a wide band-gap III-V semiconductor with ionization coefficient ratios similar to or larger than that observed in silicon.

including high refractive index contrast with its oxide material, low loss at communication wavelength regime, and significant thermo-optic coefficient for tuning. Contributed by these advantages, various photonic components have been demonstrated on integrated Si photonics platform, including mode couplers, [3][4][5][6] tunable filters, [7][8][9][10] and optical modulators. [11][12][13][14] However, Si itself is an indirect bandgap material, which limits its light emission efficiency. Laser sources on Si remain to be the challenging component for photonics integration. The requirements of an integrated laser source not only cover laser performance parameters such as optical power, threshold, pumping scheme, and stability, but also low-cost and high-volume production. Researchers are trying to come up with different ways to integrate lasers on Si. The most common way is to integrate III-V lasers on Si photonics platform, through bonding integration or direct growth approach. Alternatively, group IV materials such as germanium (Ge) and germanium tin (GeSn) alloy-based lasers show promise, with significant research progress in the past decade. Raman effect has also been explored to demonstrate lasers on Si. Such kind of laser enables lasing from the Si material itself and has drawn a lot of interest in the research community. Also, rare earth (RE) elements can be doped within photonics layer to make lasers on Si, which is similar to the idea of RE-doped optical fiber laser. RE-doped laser has the advantage of low noise and high thermal stability. Comprehensive reviews on Si-integrated lasers were published more than 6 years ago. [15,16] In the meanwhile, to the best of our knowledge, the review for the most recent progress on Siintegrated lasers covering the above-mentioned approaches is still lacking.In this review, we have summarized the recent development progress of lasers integrated on Si in the past two decades, with the focus on the wavelength regimes for communication. These lasers are categorized based on their gain media, including III-V semiconductor laser, Ge/GeSn laser, Si-based Raman laser, and RE-doped laser on Si. For III-V laser, different integration approaches are discussed, covering flip-chip integration, transfer printing integration, hybrid bonding, and direct growth method. The review is organized in the following way: it starts from background information as presented in Section 1. III-V laser, Ge/GeSn laser, Raman laser, and RE-doped laser