Abstract: To measure incredibly low light signals, you must compromise. If you want the best performance, you must select a photomultiplier tube or a superconductor. However, a photomultiplier tube is fragile and bulky, and a superconductor needs to work under low temperature. The alternative, addressing these weaknesses, is the avalanche photodiode (APD), but it is subject to poor controllability. If you need a high-speed low-noise photodetector in long-haul telecommunications, the APD is the first choice. However, the randomness process in APD limits noise performance, which restricts traffic capability.
To improve the controllability and noise performance of APDs, a band engineering design is deployed in the material lattice structure. A high-gain, low-noise APD has been demonstrated on AlN/GaN periodically stacked material. A record stable high linear gain of over 104 has been realized. ALso, an extremely low-noise APD has been demonstrated on AlInAsSb and InAlAs digital alloy. A record low excess noise factor of 0.02 has been realized on this lattice structure in a 1550-nm fiber optic window. Both devices were verified by experiments and first-principles study.