Design of High‐Speed 25 Gb/s InGaAs/AlGaAsSb Avalanche Photodiodes

There is an increasing demand for high speed 25 Gb/s low noise APDs. Semiconductors with disparate ionisation coefficients are known to provide low noise and high gain‐bandwidth product. In this work, we performed a comprehensive simulation of 400 combinations Al 0.85 Ga 0.15 As 0.56 Sb 0.44 (AlGaAsSb) avalanche width ( w m ) and InGaAs absorption width ( w a ) to identify a design to achieve high sensitivity at 25 Gb/s. Our model, which was benchmarked using experimental data in the literature, predicts that design options ranging from w m = 100 nm with w a = 700 nm to w m = 700 nm with w a = 100 nm will produce a bandwidth of at least 18.7 GHz and a gain of 10. Reducing the avalanche width to 100 nm will provide a gain‐bandwidth product > 200 GHz, without suffering from excessive band to band tunnelling current. Results from a large number of APD designs show that a sensitivity of −26.6 dBm at a wavelength of 1310 nm and a bit error rate of 1 × 10 −12 at 25 Gb/s can be achieved using a 100 nm AlGaAsSb avalanche region with a 1000 nm hybrid InGaAs absorption region (consisting of a 600 nm p‐doped and a 400 nm depleted region). This is ∼5.5 and 3.8 dB better than a commercial III–V APD and Ge/Si APD, respectively, suggesting the great potential of using AlGaAsSb avalanche photodiodes in very high bit rate optical communication.