Public defence in Photonics and Nanotechnology, M.Sc. Hanchen Liu

The title of the thesis: Development of highly sensitive Ge NIR photodiode utilizing nanotexturing and charged oxides

Thesis defender: Hanchen Liu
Opponent: Prof. Eddy Simoen, Ghent University, Belgium
Custos: Prof. Hele Savin, Aalto University School of Electrical Engineering

Near-infrared (NIR) photodetectors are key components in many modern technologies, including imaging systems, telecommunications, LiDAR for autonomous vehicles, and security applications. Germanium is an attractive material for NIR detection because its suitable bandgap. However, conventional germanium-based detectors often suffer from limited light detection efficiency due to high reflectance losses and internal electrical losses.

This thesis introduces a proof-of-concept germanium photodiode that achieves near-ideal light detection efficiency across a broad spectral range, surpassing the performance of current state-of-the-art detectors. The enhancement is attributed to the integration of surface nanostructures that significantly minimize reflectance losses, alongside the implementation of negatively charged atomic layer deposited aluminium oxide, which serves to passivate the surface and realize efficient charge collection through the induced electric field. Additionally, the photodiode is designed with a guard ring and an electrically isolated active area to suppress unwanted dark current, thereby reducing noise and enhancing detectivity.

The results demonstrate a high-performance germanium photodiode and highlight a promising approach for advancing NIR sensing technologies across diverse applications.

Keywords: Near-infrared, photodiode, nanostructured germanium, atomic layer deposition, surface passivation, quantum efficiency

Thesis available for public display 7 days prior to the defence at Aaltodoc.