Dotty enhancement for infrared sensors

Quantum dots could vastly improve night-vision goggles and infrared sensor technology, researchers claim. Devices with quantum dots could detect infrared light better at a lower cost, according to scientists at the Universities of Southern California and Texas at Austin.

Quantum dots are 3D pyramid structures made of semiconductor material around 20nm across. Electrons are trapped in an indium arsenide semiconductor, surrounded by another semiconductor, this time in gallium arsenide.

When incoming light such as infrared is absorbed by these electrons in the quantum dot they are released and transported through the semiconductor, creating current. This converts radiation into an electrical signal more efficiently than other infrared detection methods, the researchers claim.

Existing infrared technologies such as mercury cadmium telluride do not use quantum mechanical effects, said Professor Joe Campbell from Texas at Austin’s department of electrical and computer engineering.

‘This type of detector has been around for decades and is the “champion”,’ he said.

‘The problem is that mercury cadmium telluride is difficult to work with, has uniformity problems and reliability issues. People have tried to find a replacement for years.’

Quantum dots could also be tailored for use in biomedical imaging, environmental sensors, optical amplifiers, transistors, tunnelling diodes and other devices, said Campbell. ‘Better performance could be achieved by providing more efficient conversion of light into electrical current while maintaining low background noise.’

Quantum dot devices have lower dark current – leakage – than other devices and could also integrate with electronic circuits for readouts and amplification on the same chip. The dots’ sensitivity also means they could be used for multispectral imaging as well as imaging specific wavelengths such as infrared.

Campbell added that the team need to improve quantum dot performance before it can compete with ‘entrenched’ technology such as mercury cadmium telluride.

‘We still have to improve on the semiconductor wafers from which the devices are fabricated, and hopefully also develop new types of device structures that will further enhance the performance.’ The researchers plan to place the dots in a configuration called a ‘resonant cavity’ to improve their performance. This cavity traps the light and bounces it between mirrors to increase sensitivity.