Room-Temperature 15% Efficient Mid-Infrared HgTe Colloidal Quantum Dot Photodiodes

Area of Science:

• Materials Science
• Quantum Dot Technology
• Photovoltaics

Background:

• Mid-infrared HgTe colloidal quantum dot (CQD) photovoltaic devices previously demonstrated background-limited infrared photodetection at cryogenic temperatures.
• However, device efficiency significantly decreased from 20% to 1% between 150 K and 300 K.
• This reduction was tentatively attributed to a carrier diffusion length shorter than the device thickness at room temperature.

Purpose of the Study:

• To investigate the cause of reduced quantum efficiency in HgTe CQD photovoltaic devices at room temperature.
• To determine the actual carrier diffusion length and its temperature dependence.
• To identify strategies for improving room-temperature performance.

Main Methods:

• Measurement of carrier diffusion length across a range of temperatures (150 K to 295 K).
• Analysis of device efficiency in relation to series resistance and device area.
• Fabrication and characterization of reduced-area (50 by 50 μm) HgTe CQD devices.

Main Results:

• Carrier diffusion length was measured, peaking at 215 nm at 200 K and decreasing to 180 nm at 295 K, indicating it was not the primary cause of efficiency loss.
• The study identified series resistance as the main factor limiting room-temperature quantum efficiency.
• Reduced-area devices (50 by 50 μm) achieved 10-15% room-temperature quantum efficiency for specific cutoff wavelengths (4.2 μm and 3.7 μm).

Conclusions:

• Series resistance, not carrier diffusion length, is the primary limitation for room-temperature efficiency in these devices.
• Optimizing device design by reducing area significantly enhances room-temperature quantum efficiency.
• Small-area HgTe CQD devices demonstrate potential for high-performance room-temperature infrared photodetection with detectivity exceeding 10^9 Jones.