Nanocrystal optoelectronic devices

Spectroscopy and imaging in the visible region are common thanks to inexpensive silicon techologies, but the world is awash with infrared photons at equilibrium with molecular vibrations. This light holds a wealth of information and is used in such diverse applications as thermal imaging, atmospheric gas analysis and telecommunications. Standard mid-infrared imaging photodetectors are based on single-crystal HgCdTe materials, however, and they extremely expensive (> $50,000/megapixel) due to complicated manufacturing processes. This currently prevents the widespread adoption of infrared technologies in new realms such as autonomous vehicles and domestic applications. Our group actively works on developing nanocrystal quantum dot infrared detectors which rival commercial devices at a fraction of the cost. Recent advances include demonstration of high-performance photovoltaics enabling 14 milliKelvin thermal imaging, dual-band short/mid-wave infrared photovoltaics, and short-wave infrared detectors rivaling commercial devices. An introduction to infrared photodetection from a physical chemistry perspective may be found here.

To develop and improve the quantum dot detectors, we combine principles from device physics with electrodynamic and semiconductor simulations at the design stage. The detectors are then fabricated using wet chemistry and clean room techniques, and the performance is finally characterized using transport measurements and optical spectroscopies. These measurements quantify practical aspects of the device performance and also illuminate the underlying physical chemistry such as nonradiative relaxation, electrical conduction, energy levels and charging. The applied goal of nanocrystal infrared photodetection interfaces strongly with our efforts to optimize the synthesis of infrared nanocrystals and understand their fundamental transport properties.

In addition to detectors, our research focuses on the electroluminescence of quantum dots. While the quantum dots light-emitting diodes have shown promising performance in visible, emission in the mid-infrared is fundamentally more challenging because radiative rates slow down while nonradiative processes speed up. We recently demonstrated the electroluminescence from HgTe colloidal quantum dot p-n junction. Using a simple device architecture, the room-temperature electroluminescence efficiency at low current approached the limitation of the photoluminescence efficiency of the quantum dots.

Selected publications