Ge-based Single Photon Avalanche Diodes: from comprehensive characterization to advanced simulation – GeSPAD

The GeSPAD project is devoted to achieve a major breakthrough in the development of the next-generation of Single Photon Avalanche Diodes (SPAD), a high-sensitivity optoelectronic detector with many applications in X-ray tomography, biochemical sensors, DNA/protein microarray scanning, engine/turbine design, aids for disabled people, high-sensitivity and low-light cameras. In the near future, arrays of low-area SPADs will be employed for new applications in the Internet-of-Things such as user detection in smart wearable devices or in the optimization of long distance ranging for autonomous car applications. Today’s market is dominated by silicon-based SPADs, whose sensitivity is limited to photon wavelengths lower than 1100 nm. However, in order to improve depth accuracy in LiDAR systems it is highly desirable to shift the operation wavelength from 900 nm to 1500 nm, thus allowing the use of higher laser powers in compliance with eye-safety specifications.

From an industrial perspective, the germanium option is a promising solution for integration on conventional CMOS process, but significant efforts in terms of technology development are needed, and a clear benchmark of the Ge-SPAD performances against III-V and Si-based devices is still missing.
The main objective of GeSPAD is to assess novel designs of germanium-based SPAD devices, matrices and circuits and to benchmark them with their III-V and silicon counterparts. The devices designed within this project will feature enhanced infra-red photon detection probability (high quantum efficiency for wavelengths around 1310-1500 nm) as well as low dark count rates, noise and jitter.
To attain this objective, Ge-based SPADs will be inspected at all possible levels, going from material properties through device physics until circuit optimization. This project will combine advanced characterization techniques on industrial Ge-based prototypes with multi-scale predictive simulation tools, and efficient quenching circuit design. The consortium will be composed by three academic laboratories and an industrial partner, STMicroelectronics, which is one of the major CMOS-SPAD producer in the world, and intends to maintain its leadership by investing in disruptive technologies. The partners are expert in different skills and will adopt complementary methodologies: C2N (coordinator) will study the device physics of SPADs by addressing full-band quantum transport simulations and time-dependent simulations with the particle Monte-Carlo method; LAAS will perform ab-initio calculations on defect properties in Ge and Si/Ge heterostructures as well as their photoluminescence spectroscopy; Lab. Hubert Curien will develop spice models for devices and circuits; STMicroelectronics will provide the electrical characterization of in-house devices as well as TCAD simulations to optimize the SPAD architecture.
GeSPAD will have multiple repercussion on the community. From an industrial perspective, it will contribute to the design of the next generation of SPAD architecture and will very probably result in several patents. From an academic perspective, the clarification of the scientific problems here addressed will permit to gain a deeper understanding of the physics of optoelectronic devices and will result in publications in international journals and conferences. Finally, it will facilitate the creation of a French community working around SPADs.