“A class of existing infrared detectors are based on what is called ‘quantum well’ technology,” said Anupam Madhukar of the University of Southern California. “But we have created a detector based on different physics - quantum-dot physics - that works at least as well and has the potential to perform better.”
Madhukar and colleagues grew quantum dots with a base size of about 20 nm and a height of around 4 nm by molecular beam epitaxy. The quantum dots consisted of indium arsenide, gallium arsenide and an indium-gallium arsenide alloy. Each device contained 10 layers of the dots.
The researchers say their device had a detectivity of 3 x 1011 cm Hz1/2/W for radiation with a wavelength of 8.7 µm, which is “nearly 100 times higher than the previously reported peak for quantum-dot systems”. That makes it competitive with the well established quantum-well infrared photodetectors. But the quantum-dot technology is potentially cheaper as quantum dots, unlike quantum-well detectors, are able to adsorb radiation that beams straight down onto them without the need for additional processing steps.
According to Joe Campbell of the University of Texas at Austin, the quantum-dot device detectivity is about an order of magnitude lower than infrared detectors that use a third technology - mercury cadmium telluride. “These now provide the best available performance, but suffer from materials uniformity and long-term stability issues,” he said.
The researchers, who reported their work in Applied Physics Letters, believe that using a resonant cavity in combination with the quantum-dot arrays could improve their sensitivity.