High bandwidth, high responsivity waveguide-coupled germanium photo detectors for a photonic BiCMOS process

Through the last decades, telecommunication via optical fiber has been established as the backbone of intra- as well as intercontinental networks and has therefore enabled the rapid growth of the World Wide Web. Nowadays, the Internet is experiencing a revolution by the growth of social networking, streaming services, and the emerging Internet of Things. As a result, the demand for large bandwidth rises not only in long-distance communication applications but also with regard to short and medium distances reaching from a couple of meters to a few kilometers. Silicon-based photonics has the potential to revolutionize the optical communication application domain by offering high volume fabrication while being cost efficient at the same time. Further, it allows for the realization of complex and reliable systems. The combination of photonic functionality with microelectronics is seen as a key technology for future transceiver systems. Therefor monolithic integration is a very promising approach as it allows for the realization of fast and complex transceiver frontends as single chip solutions. This enables not only easy testing but also avoids additional assembly costs. The photo detector (PD) is a key component in optical communication applications. It provides the conversion from the optical to the electronic domain on the receiver side. The most widely used wavelength region in communication applications lays in the near-infrared (NIR). Here, well suited light sources are available and the attenuation in the silica fiber is sufficiently low. Through the availability of optical amplifiers optical communication over long-haul distances is enabled too. Since silicon is transparent in the near-infrared wavelength region, germanium has proven to be a well suited detector material within silicon-based photonics. In this thesis, the monolithic integration of a germanium photo detector (GePD) into a high-performance SiGe BiCMOS technology is demonstrated and discussed. The biggest integration challenge was to reach high detector performance despite certain restrictions with regard to the detector construction and fabrication which result from pursuing the goal of a modular detector integration. This means that the integration is done in a way which leaves the device parameters and yield of the BiCMOS devices nearly unchanged compared to the baseline process. In this way, the re-use of BiCMOS device models and libraries of the parent BiCMOS baseline process is enabled for the new “photonic” BiCMOS process.