Researchers Enhance Avalanche Photodiode Design for UV Detection

Geiger-mode avalanche photodiodes (GM-APDs) have seen a significant advancement in design, enhancing their sensitivity for ultraviolet (UV) photodetection. A research team led by Dr. Jonathan Schuster from the DEVCOM Army Research Laboratory in the United States published their findings in the IEEE Journal of Quantum Electronics on November 4, 2025. Their work focuses on optimizing GM-APDs to improve detection efficiency for photons in the near-ultraviolet (NUV) range.

The core mechanism of GM-APDs allows them to detect single photons by generating electron-hole pairs through a process known as impact ionization. This multiplication of charges occurs when the photodiode is biased above its breakdown voltage, producing detectable electrical pulses. To effectively capture photons, particularly at higher wavelengths where absorption is weaker, the avalanche photodiodes must achieve high unity-gain quantum efficiency (QE).

Advancements in Design Through Numerical Modeling

The research highlights the potential of 4H-silicon carbide (4H-SiC) as a material for GM-APDs, specifically for wavelengths around 280 nanometers. However, to enhance photon capture efficiency at higher wavelengths, the team recognized the need for thicker absorber layers. This requirement prompted a shift from conventional PIN architectures to a separate-absorption charge-multiplication (SACM) architecture, which presents unique engineering challenges.

Utilizing a newly developed numerical model with a calibrated material library, the researchers designed SACM APDs projected to achieve high single-photon detection efficiency in the NUV range. They explored two distinct architectural designs: non-reach-through (NRT) and reach-through (RT). Each design presented its own set of considerations and potential benefits.

Notably, the NRT-SACM APDs demonstrated a unity gain QE of up to 32%, while the RT-SACM design achieved a remarkable unity gain QE of up to 71% for photons with a wavelength of 340 nanometers. Both designs are capable of maintaining a significant electric field in the multiplication layer, crucial for Geiger-mode operation.

Design Challenges and Future Applications

Dr. Schuster emphasized the importance of balancing competing mechanisms within these designs. For the NRT-SACM architecture, specific doping profiles are necessary to maximize minority carrier diffusion length while minimizing potential barriers at the absorber layer and charge layer interface. Conversely, the RT-SACM architecture required careful modulation of charge in the charge layer to ensure effective electric field application in both the absorption and multiplication layers.

The research identified several design rules that can guide the creation of GM-APDs tailored for single-photon counting applications in the NUV wavelength range. A key takeaway is the inflexibility of charge layer designs concerning layer thickness and doping, which complicates fabrication.

The applications for 4H-SiC avalanche photodiodes are extensive, encompassing areas such as solar-blind UV detection, combustion monitoring, and environmental UV monitoring. As the numerical model continues to evolve, it holds promise for developing more sensitive and efficient APDs, paving the way for broader applications in photodetection technologies.

For further insights into the study, refer to the article by Jonathan Schuster et al., “Design Challenges in Binary 4H-SiC NUV-Enhanced SACM APDs,” published in the IEEE Journal of Quantum Electronics.