A Clearer Picture is Worth a Thousand Words

Author:  Natasha Hochlowski
Institution:  Princeton University
Date:  January 2010

We've all experienced it. Whether it was your best friend's wedding, your sister's graduation party, the family's vacation to Hawaii, or the night you went to a new restaurant with your roommates, there's always that one photo that doesn't come out. Blurred photos that are the result of poor lighting have plagued photographers both amateur and expert alike for the past 180 years. However, it may soon be possible to resolve this issue,along with those blurry photos. New research by a team of University of Toronto scientists, published in the June 19 issue of the journal Science, could spark huge advancements in the performance of electronic devices, specifically digital cameras. These advancements may solve the question of how to take a photo in an area with extremely low lighting.

The answer lies in the phenomenon of multi-exciton generation (MEG), recently explored by Professor Ted Sargent of the University of Toronto's Department of Electrical and Computer Engineering. The use of MEG may provide benefits for digital cameras and other devices incorporating semiconductors,materials that are the foundation for digital cameras, solar cells, and numerous other electronic devices.

The function of these devices centers on the absorption of photons, or particles of light. Once photons strike the semiconductor, they generate excited electrons, called excitons, which flow as a current and provide information to the device.

Exploration of MEG is the key to taking digital cameras to the next level of technological advancement. Says Sargent, "Normally, the absorption of each photon by a semiconductor results in the production of a single exciton – an excited electron and a hole,' the lower-lying electronic state that was vacated when the electron was excited. We reported a device that exploits MEG, in which multiple electrons' worth of current are obtained for each photon incident." Therefore, by employing MEG, it is possible to receive significantly more information for each photon, or particle of light, striking the camera.

Sargent's research team created the first ever light sensor to successfully benefit from MEG. This discovery is the initial step to incorporating such a sensor in pixels,small devices that translate light into information,in digital cameras.

Explains Dan Schlapbach, a professor of Photography at Loyola University Maryland, "When a photograph is taken, each pixel receives light and converts that light into a Red Green Blue (RGB) combination. Those pixel numbers are then transferred, in order, to the camera." When someone takes a photo in an area with dim lighting, the camera's sensor cannot detect anything, and it may generate or incorrect RGB combinations,leading to the dark, dim, blurry photos that plague us on a regular basis.

With the use of MEG, each photon can provide multiple electrons' worth of current, allowing the camera to have increased sensitivity. Thus, under conditions of low lighting, cameras will be better able to pick up on signals, providing photos that are significantly clearer.

Digital cameras are not the only devices that may see improvements due to MEG. Sargent also visualizes MEG as a viable phenomenon for the use in solar cells, because "in photovoltaics, more current per photon could potentially translate into more efficient conversion of the sun's energy into electrical power." Photovoltaics, or the study of converting the sun's energy into electricity, would thus be able to produce greater amounts of electricity with the same amount of energy from the sun.

Although these new advances still require much research and development before they are commercially employed, researchers should start to see more conclusive results in the near future,and our crystal clear photos won't be far behind. Concludes Sargent, "Multi-exciton generation breaks the conventional rules that bind traditional semiconductor devices. This finding shows that it's more than a fascinating concept: the tangible benefits of multiple excitons can be seen in a light sensor's measured current."