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

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A single photon avalanche diode (SPAD) with an InGaAs absorption region, and an InAlAs avalanche region was designed and demonstrated to detect 1550 nm wavelength photons. The characterization included leakage current, dark count rate and single photon detection efficiency as functions of temperature from 210 to 294 K. The SPAD exhibited good temperature stability, with breakdown voltage dependence of approximately 45 mV K−1. Operating at 210 K and in a gated mode, the SPAD achieved a photon detection probability of 26% at 1550 nm with a dark count rate of 1 × 108 Hz. The time response of the SPAD showed decreasing timing jitter (full width at half maximum) with increasing overbias voltage, with 70 ps being the smallest timing jitter measured.

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We report the effects of ex situ thermal annealing on the deep-level defects and the minority-carrier electron diffusion length in Be-doped, p-type In0.03Ga0.97As0.99N0.01 grown by solid source molecular-beam epitaxy. Deep-level transient spectroscopy measurements reveal two majority-carrier hole traps, HT1 (0.18 eV) and HT4 (0.59 eV), and two minority-carrier electron traps, ET1 (0.09 eV) and ET3 (0.41 eV), in the as-grown sample. For the sample with postgrowth thermal annealing, the overall deep-level defect-concentration is decreased. Two hole traps, HT2 (0.39 eV) and HT3 (0.41 eV), and one electron trap, ET2 (0.19 eV), are observed. We found that the minority-carrier electron diffusion length increases by ∼30% and the leakage current of the InGaAsN∕GaAsp-n junction decreases by 2–3 orders after thermal annealing. An increase of the net acceptor concentration after annealing is also observed and can be explained by a recently proposed three-center-complex model.