“Digital
cameras are now universal, but they suffer from a major limitation: they take
poor pictures under dim light. One reason for this is that the image sensor
chips inside cameras collect, at most, one electron’s worth of current for
every photon (particle of light) that strikes the pixel,” says Ted
Sargent, professor in U of T’s Department of Electrical and Computer
Engineering.
“Instead
generating multiple excitons per photon could ultimately lead to better
low-light pictures.”
In solar cells
and the CMOS chips of digital cameras, particles of light – known as photons – are
absorbed in a semiconductor, such a silicon, and generate excited electrons,
known as excitons. The semiconductor chip then measures a current that flows as
a result. Normally, each photon is converted into at most one exciton. This
lowers the efficiency of solar cells and it limits the sensitivity of digital
cameras. When a scene is dimly lit, small portable cameras like those in
laptops suffer from noise and grainy images as a result of the small number
excitons.
“Multi-exciton generation breaks the conventional
rules that bind traditional semiconductor devices,” says Sargent.
“This finding shows that MEG is more than a fascinating concept: the
tangible benefits of multiple excitons can be seen in a light sensor’s measured
current.”
