A 2x2 Pixel Array Camera based on a Backside Illuminated Ge-on-Si Photodetector

This paper proposes a new concept of a Near-Infrared (NIR) micro-system camera with a backside illuminated Germanium-on-Silicon (Ge-on-Si) photodetector. The performance of this photodetector is analyzed and compared to frontside illuminated Ge-on-Si photodetectors. An enhanced responsivity of 0.4 A/W at 1310 nm for the backside illuminated diode is achieved, which is equal to commercial solutions. With the help of zero-biasing, the critical dark current density can be reduced by more than a factor of 80 000 compared to standard biasing with −1 V. By using a backside illuminated diode, reflections of the metal layer are eliminated and the pixel fill factor is increased. Additionally, a proof of concept micro-system with a 2 x 2 pixel array of Ge-on-Si backside illuminated photodetectors and a custom readout ASIC is demonstrated. This proves the functionality of the proposed photodetector and readout concept for NIR camera applications.