Fabrication, Design and Noise Analysis of a High-Gain Waveguide-Coupled Photoconductive Detector

Abstract

In the field of silicon photonics, it has only recently become possible to build complex systems. As system power constraints and complexity increase, design margins will decrease--making understanding device noise performance and device-specific noise origins increasingly necessary. Approaches to increased photodetector responsivity are also of great importance, since they can significantly improve overall system performance. The design, theory, fabrication and testing of a waveguide-coupled germanium MSM photodetector with an above-unity quantum efficiency of approximately 140% is presented, capable of 1.1 GHz operation. The current amplification comes from the photoconductive multiplication effect. The noise elbow at 5V bias is measured to be approximately 150MHz and the high frequency detector noise approaches the Johnson noise floor. I demonstrate for the first time that Ge on Si based photoconductors are not limited by shot noise, as conventional PIN detectors are, but in fact achieve lower noise figures of merit.