Low-Energy Ion Implantation and Deep-Mesa Si-Avalanche Photodiodes with Improved Fabrication Process.

Since the avalanche phenomenon was first found in bulk materials, avalanche photodiodes (APDs) have been exclusively investigated. Among the many devices that have been developed, silicon APDs stand out because of their low cost, performance stability, and compatibility with CMOS. However, the increasing industrial needs pose challenges for the fabrication cycle time and fabrication cost. In this work, we proposed an improved fabrication process for ultra-deep mesa-structured silicon APDs for photodetection in the visible and near-infrared wavelengths with improved performance and reduced costs. The improved process reduced the complexity through significantly reduced photolithography steps, e.g., half of the steps of the existing process. Additionally, single ion implantation was performed under low energy (lower than 30 keV) to further reduce the fabrication costs. Based on the improved ultra-concise process, a deep-mesa silicon APD with a 140 V breakdown voltage was obtained. The device exhibited a low capacitance of 500 fF, the measured rise time was 2.7 ns, and the reverse bias voltage was 55 V. Moreover, a high responsivity of 103 A/W@870 nm at 120 V was achieved, as well as a low dark current of 1 nA at punch-through voltage and a maximum gain exceeding 1000.