Ultralow Gain-Normalized Dark Current Density in a Colloidal Quantum Dot Avalanche Photodiode with a SACM...

Area of Science:

• Materials Science
• Optoelectronics
• Semiconductor Physics

Background:

• Short-wave infrared (SWIR) avalanche photodiodes (APDs) are crucial for advanced technologies like LiDAR, free-space optical communication, and low-light imaging.
• Colloidal quantum dots (CQDs) present a promising, silicon-compatible material for SWIR APDs due to their solution-processability.
• Conventional CQD p-i-n APDs suffer from high dark current under reverse bias because photon absorption and avalanche multiplication occur in the same layer.

Purpose of the Study:

• To design and demonstrate a novel CQD/i-ZnO APD utilizing a separate-absorption-charge-multiplication (SACM) architecture.
• To suppress tunneling-induced dark current by spatially separating the absorption and multiplication regions.
• To achieve high-performance SWIR APDs with significantly reduced dark current and enhanced detectivity.

Main Methods:

• Fabrication of a CQD/i-ZnO photodiode employing the SACM architecture.
• Strategic placement of the high-field multiplication region within the wide-bandgap i-ZnO layer, distinct from the CQD absorption layer.
• Characterization of the device performance, including gain-normalized dark current density and specific detectivity.

Main Results:

• The SACM architecture effectively suppresses dark current by relocating the multiplication region to i-ZnO.
• Achieved a gain-normalized dark current density of 4.86 × 10^-7 A cm^-2, the lowest reported for CQD photodetectors with internal gain.
• Obtained a specific detectivity of 1.15 × 10¹² Jones, indicating excellent sensitivity.

Conclusions:

• The SACM architecture is a highly effective strategy for developing low-dark-current CQD-based SWIR APDs.
• This approach overcomes the limitations of conventional CQD APDs, paving the way for improved SWIR optoelectronic devices.
• The demonstrated device performance highlights the potential of CQD/i-ZnO heterostructures for next-generation imaging and communication systems.