Characterization of Mid-Infrared HgTe Colloidal Quantum Dot Photodiodes

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optoelectronics

Background:

• Mid-infrared HgTe colloidal quantum dot (CQD) photodiodes are promising for various applications.
• Understanding illumination configuration effects (top vs. back) is crucial for optimizing photodiode performance.
• Recombination mechanisms significantly influence photodiode efficiency and detectivity.

Purpose of the Study:

• To compare the performance of top-illuminated and back-illuminated HgTe CQD photodiodes.
• To investigate the temperature-dependent behavior and recombination mechanisms in these devices.
• To identify factors limiting photodiode performance at different temperatures.

Main Methods:

• Fabrication and characterization of top- and back-illuminated HgTe CQD photodiodes.
• Temperature-dependent measurements of current-voltage (IV) characteristics and external quantum efficiency (EQE).
• Analysis of recombination mechanisms using diode models and activation energy calculations.

Main Results:

• Back-illuminated diodes exhibit significantly higher EQE and detectivity at room temperature (290 K) compared to top-illuminated diodes.
• Both configurations show peak efficiencies around 110 K, with back-illuminated diodes achieving higher peak efficiencies (67% vs. 38%).
• Above 140 K, geminate recombination dominates, while below 140 K, trap-like recombination becomes significant. A photoconductive shunt resistance, attributed to hopping transport in CQDs, limits low-temperature performance.

Conclusions:

• Back-illumination offers superior performance for HgTe CQD photodiodes due to optimized light coupling and charge collection.
• The study elucidates the transition in dominant recombination mechanisms with temperature, from geminate to trap-assisted.
• Hopping transport in CQDs is identified as a critical factor limiting low-temperature performance, suggesting strategies for future material and device engineering.