Novel Silicon Epitaxy-Based Avalanche Photodetectors With Parameter-Sensitivity Engineering for Enhanced Fabrication Robustness

Avalanche photodetectors (APDs) are prized for their high gain, fast response, excellent sensitivity, and cost-effectiveness. However, the conventional fabrication methods that rely on complex and expensive high-energy ion implantation introduce lattice defects, leading to increased dark current. This study presents a novel silicon epitaxy-based APD structure and fabrication approach that employs thin silicon epitaxy combined with low-energy ion implantation to form the multiplication region. This method avoids the need for expensive high-energy ion implantation equipment. The prototype for the first trial achieved a 20 V breakdown voltage (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>b</i></sub>), 0.43 A/W responsivity (830 nm, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> = 1), and 64% quantum efficiency (QE). Secondary ion mass spectrometry (SIMS) analysis and simulations revealed that deviations in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i>-well junction depth and variations in doping concentration significantly affect both breakdown voltage and gain characteristics. To mitigate the sensitivity of implantation fluctuations, the study proposes a structural optimization approach focusing on lower <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i>-well doping concentrations and deeper junction depths. Simulation results indicate that this structure can achieve a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i>-well junction depth variation of 0.7 μm, corresponding to a breakdown voltage variation within 100 V, while maintaining a high gain. Combined with a silicon epitaxy-based fabrication process, this approach significantly enhances the robustness of APD fabrication. By adjusting the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i>-well ion implantation energy, APDs with breakdown voltages of 90, 125, and 175 V were successfully achieved.