Planar Tandem APD Array for Free Space Laser Communications Applications

Enlarging the active window size of the photodetector (PD) while sustaining its high-speed and high-responsivity performances is the key to achieving a high-performance photo-receiver with a large field-of-view (FoV) angle for application in a free space laser communication system. However, in the traditional PD structure, a large active area always leads to a pronounced degradation in the RC-bandwidth. Using a tandem layout for high-speed p-i-n PD arrays solves the problem, but it reduces the responsivity for high-speed and large FoV performance, as current balancing between the different p-n junctions is needed. Here, for the first time, novel tandem APD arrays are demonstrated which relax the fundamental trade-offs among window size, responsivity, and speed. Our flip-chip packaged 3 $ \times $ 3 arrays with a window size of 0.12 mm can simultaneously achieve a, high-responsivity (1.2 A/W), wide-bandwidth (6 GHz), and large GBP (150 GHz).