Photodevice detects color with metal grating
The researchers make the point that the approach is closer to that used by human eye and allows color selectivity to be integrated into the photodetector.
The device uses two Schottky junctions to accumulate charge in an energy well which results in photocurrent gain and a plasmonic aluminum grating for photocurrent enhancement and red–green–blue color selectivity. The device is described online in a new study in the journal Advanced Materials.
Conventional CMOS image sensors are turned into color image detectors by adding dielectric or dye color filters, which have the disadvantage of requiring multipass processing, tend to degrade under exposure to sunlight and can be difficult to align with the sensor pixels.
Following research at Rice University Image sensors could amplification and filtering integrated directly into pixels. Source: Bob Zheng/Rice University.
Researcher Bob Zheng was looking into camouflage systems and came up with a color photodetector that uses a combination of band engineering and plasmonic gratings, comb-like aluminum structures with rows of parallel slits. The aluuminum is deposited on top of a thin oxide coating on top of the sensor pixel array.
By tuning the oxide thickness and the width and spacing of the slits, Zheng was able to preferentially direct different colors of light into the silicon photodetector or reflect it back into free space.
The light-filtering slits in the grating are about 100 nanometers wide. Source: Bob Zheng/Rice University.
"With plasmonic gratings, not only do you get color tunability, you can also enhance near fields," said Zheng, in a statement. "The near-field interaction increases the absorption cross section, which means that the grating sort of acts as its own lens. You get this funneling of light into a concentrated area. Not only are we using the photodetector as an amplifier, we’re also using the plasmonic color filter as a way to increase the amount of light that goes into the detector," he said.
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