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Quantum Dots Form Heart of IR Detector

Photonics Spectra
Jul 2004
Daniel S. Burgess

A collaboration of the University of Southern California in Los Angeles and the University of Texas at Austin has produced a quantum-dot photodetector for use in the 8- to 12-µm atmospheric window. The performance of the cooled device is competitive with that of current quantum-well infrared photodetectors and approximately an order of magnitude lower than that of well-established HgCdTe intrinsic-type detectors, suggesting its suitability for applications in the near-term such as night vision, target-tracking and environmental monitoring.

Quantum Dots Form Heart of IR Detector
An infrared photodetector based on InAs quantum-dot displays shows potential for use in the 8- to 12-µm atmospheric window. Courtesy of the University of Southern California.

Photodetectors based on quantum dots have attracted interest as alternatives to quantum-well-based devices for IR imaging. The three-dimensional confinement of charge carriers in these minute bits of semiconductor makes them extremely sensitive to incident radiation, including the radiation perpendicular to the plane of the active region that quantum-well devices miss without additional processing steps. The long carrier lifetimes in the dots also suggest that optimized detectors should display high responsivities, high operating temperatures and low dark currents.

In the work, the researchers fabricated the quantum-dot infrared photodetector by molecular beam epitaxy. The device features 10 layers of undoped InAs dots surrounded by InGaAs and GaAs and sandwiched by Si-doped GaAs contact layers. InGaAs grown by migration enhanced epitaxy caps this active region.

Operating at 78 K, the device displays a detectivity as high as 3 × 1011 cm Hz1/2/W and a signal-to-noise ratio of less than 1014 A/Hz1/2. The team predicts that operating temperatures of 100 K should be possible and expects that placing it in a resonant cavity will increase the sensitivity.


GLOSSARY
atmospheric window
A range of wavelengths within which radiation transmitted through the atmosphere suffers relatively little absorption by atmospheric gases.
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