The performance of the photodetector is often the primary limiting factor affecting a free space communication or LiDAR system's sensitivity. Avalanche photodiodes (APDs) can be used to improve the signal to noise ratio (SNR) compared to conventional p-i-n photodiodes. Our study focuses on demonstrating an APD operating in the eye-safe short-wave infrared (SWIR) spectrum (>1400 nm) with high multiplication (M>1200) and low excess noise (F<7 at M=200) at room temperature. This device utilizes GaAsSb and Al0.85Ga0.15AsSb in a separate absorber, charge, and multiplication (SACM) configuration on an InP substrate. Notably, this device exhibits more than 40 times improvement in maximum achievable multiplication and 6.5 times lower excess noise at M=25 compared to commercially available InGaAs/InP devices.
Avalanche photodiodes (APDs) capable of operating at telecommunication wavelengths usually utilize an InGaAs absorber and a multiplication region of InP or InAlAs. Since the electron and hole ionization coefficients (α and β respectively) in these multiplication regions are very similar they suffer from high excess noise, limiting their sensitivity. In recent years, there have been a number of reports of Sb containing III-V semiconductor alloys that appear to show very low excess noise characteristics, similar to or better than that obtained in silicon. These reports show that AlInAsSb grown on GaSb appears to show a β/α ratio of ~0.015. Both AlAsSb and Al0.85Ga0.15As0.56Sb0.44 grown lattice matched on InP also show β/α values that vary from 0.005-0.01. The exception to this appears to be AlGaAsSb grown lattice matched on GaSb where a β/α ratio of ~2.5 has been seen. This paper reviews the published results in this area.
Avalanche photodiodes (APDs) are used in high-speed data communication and light detection and ranging (LIDAR) systems due to their high sensitivity and high speed. However, InAlAs and InP based APDs have relatively high excess noise because they have relatively similar electron and hole ionization coefficients (α and β respectively). Here, we report on an ultra-low excess noise material Al0.85Ga0.15As0.56Sb0.44 (hereafter AlGaAsSb) with a k value (β/α) of 0.01. The excess noise and multiplication measurements were performed on both random alloy (RA) p+-i-n+ and digital alloy (DA) grown p+-i-n+ diodes with depletion regions of 1020nm and 890nm respectively. The excess noise was found to be broadly similar in both RA and DA grown structures.
A series of AlAsSb p+-i-n+ and n+-i-p+ diodes with varying i-region thickness from 0.08μm to 1.55μm have been used to determine the temperature dependent impact ionization coefficients by performing avalanche multiplication measurements from 210K to 335K. The increase in electron and hole ionization coefficients as the temperature decreases is much smaller when compared to InAlAs and InP. This leads to a much smaller avalanche breakdown variation of 13mV/K in a 1.55μm p+- i-n+ diode. For a 10Gb/s InGaAs/AlAsSb separate absorption and multiplication avalanche photodiode (SAM-APD), the variation in breakdown voltage is predicted to be only 15.58 mV/K.
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