Breitbandiger, hocheffizienter Photodetektor basierend auf dem SiGe-Materialsystem
Final Report Abstract
During the last five years the INT and IHT of the University of Stuttgart have worked together to research, develop and characterise SiGe-photodetectors integrated on Si and SOI substrates. DC measurements on wafer are realized to determine the performance of the photodiodes for different bias voltages. The new photodiodes developed in this project by IHT show a decrease of the dark current and an improvement in the responsivity with respect to previous projects. The responsivity reaches R = 115 mA/W at the bias voltage Vbias = -1 V with a wavelength of 1550 nm. The new fabrication process which is responsible for the improvements is described in the final report of the cooperation partner IHT. Measurements in the frequency domain are realised using two different measurement setups, optical heterodyne setup and a vector network analyser. Due to the high potential of the HET setup for the realisation of high frequency measurements, a calibration process is developed in order to eliminate the influence of the electrical and optical components of the setup in the measurement results. The measurements of photodiodes with different upper mesa radius show that the capacitance of the photodiode is lower for smaller areas. For photodiodes with 5 µm radius a 3-dB bandwidth higher than 40 GHz is achieved. After the characterisation of the photodiodes on wafer, three different designs are developed to integrate a photodiode on board. The goal of this approach is to integrate on board a high speed photodiode together with a TIA to get a high speed optical receiver. A board is designed to integrate a photodiode with a radius of 5 µm next to a 72 GHz bandwidth TIA designed at the INT. A substrate carrier is specifically fabricated to avoid long bond wires between the two devices to achieve high bandwidth performance of the integrated receiver. An integration of the optical and electrical part (photodiode and TIA) is successfully measured achieving a high 3-dB bandwidth of 22 GHz. This project demonstrates a high bandwidth optical receiver using a photodiode fabricated with a tensile strength process in the absorption layer with higher responsivity and similar bandwidth than the photodetectors fabricated in the previous projects.
