Researchers in Singapore reported that they’ve created a graphene photodetector that is roughly 800 times more sensitive than previous graphene photodetectors, and around 10 times more sensitive than the CMOS-based sensors in today’s digital cameras.
We have long known that graphene, along with being incredibly strong and electrically conductive, also has the ability to absorb light over a very broad wavelength range. Furthermore, researchers have recently confirmed that graphene has a very sensitive, hot carrier response to light (multiple electrons are fired off for every photon that hits a sheet of graphene). Both of these properties make graphene, in theory, perfect for camera sensors, photovoltaic cells, and fiber-optic communications. Now, it seems, researchers at Nanyang Technological University have actually proven it in practice.
The Singaporean graphene photodetector has a photoresponsivity of 8.61 A/W, up from previous graphene photodetectors which only manage 10 mA/W — or an increase in sensitivity of around 860 times. Hard data for silicon photodetectors, as found in your digital camera, is hard to come by, but the average seems to be around 0.8 A/W — or around 10 times less sensitive than the new graphene photodetector. This new sensor is also sensitive to a wide range of wavelengths, including visible, and near- and mid-infrared light. To achieve such high sensitivity, the researchers first create a transistor with a graphene monolayer (one-atom-thick) channel. They then deposit a varying-thickness layer of titanium on top of the graphene. This titanium layer is then etched away, leaving an array of graphene quantum dot-like (GQD) structures. This GQD then acts as the photodetector: When photons hit the GQD, the transistor turns on. Strap enough of these graphene transistors together and voila: You now have an imaging sensor.
In reality, though, and contrary to some big-name publications, this graphene sensor isn’t going to replace the silicon sensor in your camera. Graphene is still incredibly hard to work with on a commercial scale (here the researchers are still mechanically exfoliating graphene and placing it on a silicon substrate with tweezers), and there’s no indication that this method would ever scale up. What is far more likely is that these graphene photodetectors might be used in optoelectronics, where optical and electronic components are squeezed into the same system/chip, or in enabling faster fiber-optic networks.
Via Dr. Stefan Gruenwald