In a recently published paper in 《Light: Science & Applications》 a team led by Professor Martyniuk from the Military University of Technology in Poland along with collaborators from the Shanghai Institute of Technical Physics of Chinese Academy of Sciences, presented the current status and future outlook on infrared APDs. The paper encompasses bulk HgCdTe and AIIIBV material systems, including the renowned “third wave” superlattice materials.

Avalanche photodiodes (APDs) have attracted extensive attention due to their excellent time response and high sensitivity in optical communication systems. APDs amplify weak optical signals through an internal gain mechanism of impact ionization. Key metrics to evaluate APDs include gain-bandwidth product and excess noise.

Materials like InGaAs, HgCdTe, and superlattices have been applied to APDs in the infrared spectrum. Emerging 2D materials such as black phosphorus and InSe also show potential. Strategies to improve APD performance include using materials with favorable ionization properties, reducing avalanche region thickness, and impact ionization engineering.

APDs can also work in single photon mode as single photon avalanche detectors (SPADs) for photon counting and quantum applications. APD and SPAD technologies are evolving from traditional bulk materials towards lower dimensional structures like superlattices and 2D materials to enhance metrics like gain, noise, speed, and operating wavelength.

Specifically, InGaAs provides lower noise and faster response compared to Ge. The development of HgCdTe and superlattices has enabled new passive/active detection functionalities. In active imaging systems, APDs can amplify signals before entering the readout circuit. Additionally, combining dual-band detection and multiplication gain is key for achieving dual-band detection over a wide temperature range.

When biased above breakdown voltage, a single photon can trigger an avalanche in APDs for single photon detection. Such single photon avalanche detector (SPAD) mode is more sensitive than photomultiplier tubes, but additional photons are not counted during the pulse. SPADs compete with superconducting nanowire single photon detectors to meet the stringent requirements of quantum optical applications.

2D material heterostructures can also be leveraged to fabricate avalanche multiplication and single photon counting technologies. These materials have low absorption but combining with photonic structures can realize high absorption graphene detectors. Compared to traditional materials, 2D materials exhibit superior flexibility, light coupling, and self-passivation. Exploring new materials for low-field avalanche multiplication holds significance for high-efficiency APD devices.