A Low-Voltage Si-Ge Avalanche Photodiode for High-Speed and Energy Efficient Silicon Photonic Links

Silicon-germanium (Si-Ge) avalanche photodiodes (APDs) have large gain bandwidth product (GBP) and low excess noise due to the lowimpact ionization coefficient ratio of silicon. Optical receivers usingAPDsare able to achieve high-speed and energy efficient optical transceiver systems. We demonstrate a waveguide Si-GeAPDwith lowbreakdownvoltage of-10V, achieving 60Gb/s PAM4 successfully. A compact APD circuit model was constructed to allow photonic devices and transceiver circuitry co-design. The APD receiver has achieved -16 dBm sensitivity at 50 Gb/s PAM4 with a bit error rate (BER) of 2.4 x10(-4). The sensitivity of APD receivers changes with the multiplication gain. In our analysis, compared to a PIN PD receiver the APD receiver operating at optimum gain can obtain similar to 8 dBmore sensitivity for NRZ signaling at <50 Gb/s and 3-4 dB more sensitivity for PAM4 signaling at 50-100 Gb/s. Also, the APD receiver operating at optimum gain can reduce power consumption by similar to 10% at PAM4 data rates of 50 Gb/s and similar to 15% at 100 Gb/s in a silicon carrier-depletion microring modulator basedWDM photonic link.