Understanding defect generation/recombination processes in Ge-on-Si photodetectors

Optical receivers based on high opto-electrical bandwidth, high responsivity and low dark current germanium photodetectors, substantially enhance the performance of Si-based optical interconnects, where the performance of these Ge waveguide p-i-n photodetectors have been boosted by recent achievements in the epitaxial growth of Ge on Si. During operation, at use conditions, Ge photodetectors are being supplied with a bias-voltage in reverse mode, where their dark current needs to remain low, to ensure a high signal-to-noise ratio. The degradation mechanisms that drive the increase of dark current are very complex, especially for devices with geometries leading to local field enhancements, in critical regions of the device; the so called Avalanche-Photodetectors are a key example. The understanding of the conduction and degradation mechanisms of such Ge photodetectors is the main topic of this PhD-study. Questions like: What defects drive the conduction in these devices and what are their electrical properties? Can such defects be passivated and, if yes, under what conditions? Which energies are required for defect generation? What physics accurately model the carrier transport necessary to calculate defect generation rates? will need to be addressed.