Researchers Enhance Avalanche Photodiode Design for UV Detection

Researchers at the DEVCOM Army Research Laboratory have made significant strides in optimizing the design of avalanche photodiodes (APDs) for enhanced photodetection in the ultraviolet (UV) wavelength range. The study, published on November 4, 2025, in the IEEE Journal of Quantum Electronics, focuses on improving the performance of Geiger-mode avalanche photodiodes (GM-APDs) that can detect single photons.

The challenge lies in the ability of GM-APDs to absorb photons efficiently, particularly in the deep-ultraviolet (DUV) spectrum around 280 nanometers. These devices work on the principle of impact ionization, where absorbed photons create electron-hole pairs, leading to a multiplication of charges in an electric field. For effective detection, the APDs must achieve high quantum efficiency (QE) at the desired wavelengths.

While certain GM-APDs based on 4H-silicon carbide (4H-SiC) show promise in DUV detection, the researchers have identified that improving photon capture efficiency in the near-ultraviolet (NUV) range requires thicker absorber layers. Traditional designs often fall short due to their limited thickness, which typically measures less than 3 micrometers. Dr. Jonathan Schuster and his team propose a shift to a separate-absorption charge-multiplication (SACM) architecture that accommodates absorber layers tens of micrometers thick.

Innovative Architectural Designs for Enhanced Performance

This new approach presents unique design challenges, primarily related to the transition from conventional architectures to those with thicker absorber layers. Dr. Schuster explains, “Switching to SACM architecture necessitates a departure from existing designs, which can complicate fabrication.” The research team has developed a numerical model that utilizes a calibrated 4H-SiC material library to tackle these challenges.

The researchers explored two architectural designs: non-reach-through (NRT) and reach-through (RT). Each design offers distinct advantages, particularly in terms of quantum efficiency. The NRT-SACM APDs demonstrated a unity gain QE of up to 32% for photons at 340 nanometers, while the RT-SACM design achieved an impressive 71% unity gain QE. These advancements enable the devices to maintain substantial electric fields necessary for Geiger-mode operation.

The study emphasizes the importance of engineering doping profiles to optimize performance. For NRT-SACM designs, achieving a balance between maximizing minority carrier diffusion and minimizing potential barriers at the absorber layer/charge layer interface is crucial. In contrast, the RT-SACM architecture requires careful modulation of charge in the charge layer to maintain a sufficient electric field for avalanche breakdown.

Broader Applications and Future Implications

The findings from this research could significantly broaden the applications of 4H-SiC avalanche photodiodes in various fields. Potential uses include solar-blind UV detection, combustion monitoring, and environmental UV monitoring. The advancements in photon detection capabilities will likely facilitate more sensitive and efficient devices, which could have a profound impact on both scientific research and practical applications.

Dr. Schuster and his team have established several design rules that can guide the future development of GM-APDs tailored for single-photon counting in the NUV wavelength range. As the researchers noted, the rigidity of charge layer designs in APDs poses challenges in terms of layer thickness and doping variations, complicating fabrication processes.

As this research progresses, the numerical model developed could serve as a foundational tool for further innovations in avalanche photodiode technology, paving the way for enhanced detection mechanisms in ultraviolet applications. With continued advancements, researchers hope to unlock new possibilities in photon detection, benefiting a range of scientific and industrial sectors.