Si-microstructures for back-illuminated Ge-on-Si photodetectors

The silicon technology is the big driver for photonic devices. According to many investigations in the field of thin-film technology, by now it is possible to implement a variety of common infrared detection materials on silicon substrates. Front-illuminated sensors usually suffer from angular and area limitations due to the presence of multiple metal and dielectric layers for the purpose of contacting and readout electronics located on top of the sensor region. Hence, the substantial advantage of backside illumination is the increase of photo-active area and numerical aperture, and the possible integration of optical microstructures on the backside. Therefore we developed back-illuminated Ge-on-Si photodiodes. The transparency of silicon in the infrared range (λ > 1.1 µm) allows the lossless propagation of incoming light, passing through the Si-substrate towards the front side located Ge detection material. In addition, we explore the usage of light trapping microstructures to increase the quantum efficiency of the photodiodes. As a candidate with high potential, we designed and integrated so called black silicon and investigated a further improvement of the photodiode performance