The optical detector used in pulsed LIDAR, range finding and optical time domain reflectometry systems is typically the limiting factor in the system's sensitivity. It is well-known that an avalanche photodiode (APD) can be used to improve the signal to noise ratio over a PIN detector, however, APDs operating at the eye-safe wavelengths around 1550 nm are limited in sensitivity by high excess noise. The underlying issue is that the impact ionization coefficient of InAlAs and InP used as the avalanche region in current commercial APDs are very similar at high gain, leading to poor excess noise performance. Recently, we have demonstrated extremely low noise from an Al(Ga)AsSb PIN diode with highly dissimilar impact ionization coefficients due to electron dominated impact ionization.In this paper, we report on the first low noise InGaAs/AlGaAsSb separate absorption, grading and multiplication APDs operating at 1550 nm with extremely low excess noise factor of 1.93 at a gain of 10 and 2.94 at a gain of 20. Furthermore, the APD's dark current density was measured to be 74.6 µA/cm 2 at a gain of 10 which is competitive with commercial devices. We discuss the impact of the excess noise, dark current and responsivity on the APDs sensitivity and, project a noise-equivalent power (NEP) below 80 fW/Hz 0.5 from a 230 µm diameter APD and commercial transimpedance amplifier (TIA). The prospects for the next generation of extremely low noise APDs for 1550 nm light detection are discussed.

The optical detector used in pulsed LIDAR, range finding and optical time domain reflectometry systems is typically the limiting factor in the system's sensitivity. It is well-known that an avalanche photodiode (APD) can be used to improve the signal to noise ratio over a PIN detector, however, APDs operating at the eye-safe wavelengths around 1550 nm are limited in sensitivity by high excess noise. The underlying issue is that the impact ionization coefficient of InAlAs and InP used as the avalanche region in current commercial APDs are very similar at high gain, leading to poor excess noise performance. Recently, we have demonstrated extremely low noise from an Al(Ga)AsSb PIN diode with highly dissimilar impact ionization coefficients due to electron dominated impact ionization.In this paper, we report on the first low noise InGaAs/AlGaAsSb separate absorption, grading and multiplication APDs operating at 1550 nm with extremely low excess noise factor of 1.93 at a gain of 10 and 2.94 at a gain of 20. Furthermore, the APD's dark current density was measured to be 74.6 µA/cm 2 at a gain of 10 which is competitive with commercial devices. We discuss the impact of the excess noise, dark current and responsivity on the APDs sensitivity and, project a noise-equivalent power (NEP) below 80 fW/Hz 0.5 from a 230 µm diameter APD and commercial transimpedance amplifier (TIA). The prospects for the next generation of extremely low noise APDs for 1550 nm light detection are discussed.

We report the impact ionisation coefficients of the quaternary alloy Al0.9Ga0.1As0.08Sb0.92 lattice matched to GaSb substrates within the field range of 150 to 550 kVcm -1 using p-i-n and n-i-p diodes of various intrinsic thicknesses. The coefficients were found with an evolutionary fitting algorithm using a non-local recurrence based multiplication model and a variable electric field profile. These coefficients not only indicate that an avalanche photodiode can be designed to be function in the midwave infrared, but also can be operated at lower voltages. This is due to the high magnitude of the impact ionisation coefficients at relatively low fields compared to other III-V materials typically used in avalanche multiplication regions.

Extended short-wave infrared (SWIR) avalanche photodiodes based on III–V quaternary alloys were grown on GaSb. An InGaAsSb absorber allowed for cut-off wavelengths of 2.2 μm and 2.75 μm, at 77 K and 300 K, respectively. A multiplication layer of AlGaAsSb with Al = 0.9 mole fraction was used, a material recently characterized by our group, allowing for a breakdown voltage of less than 15 V. Linear and 2D arrays were fabricated using BCl3 dry and HF wet-chemical etching, and dielectric passivation layers were tested. These results indicate that extended SWIR single photon detectors can be developed.

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