Sensitivity of high-speed receivers using InAlAs avalanche photodiodes

Indium Phosphide (InP) avalanche photodiodes (APDs) are widely used in receivers for high-speed direct-detection lightwave communication systems. However, the material In_0.52Al_0.48As (InAlAs) is considered as an avalanche material superior to InP due to lower excess noise factors in InAlAs than that in InP . APDs using InAlAs avalanche region have thus been researched widely. To compare the performance of InP and InAlAs APDs in high-speed operations, this paper evaluates the receiver sensitivity at a certain BER rigorously and with the inclusion of intersymbol-interference (ISI) in the analysis, instead of simply relying on a single APD performance parameter such as the commonly used excess noise factor, which is a measure of uncertainty in the avalanche gain. This paper uses a model that builds upon the rigorous ISI and BER model by including tunneling current noise as well as TIA noise, to carry out sensitivity calculations for InAlAs APDs of varying w. This allows the establishment of an optimum avalanche region and associated best sensitivity for 10Gbit/s systems. In turn, the model enables straightforward comparisons to be made between optimized InAlAs APDs and InP APDs.