InAlAs APD with high multiplied responsivity-bandwidth product (MR-bandwidth product) of 168 A/W.GHz for 25 Gbit/s high-speed operations

An InAlAs avalanche photodiode (APD) that has large bandwidth (>18.5 GHz) and high multiplied responsivity is demonstrated. The APD has a vertically illuminated structure with a thick absorption layer of 1 μm. The fabricated APD achieves the maximum 3 dB bandwidth of 23 GHz at the multiplied responsivity of 4.06 A/W and the 3 dB bandwidth of 18.5 GHz at high multiplied responsivity of 9.1 A/W. The multiplied responsivity-bandwidth product 18.5 × 9.1 = 168 A/W-GHz is the largest value ever reported for an APD for 25 Gbit/s operations.