Researchers at Georgia State University have figured out how to get a semiconductor to detect low-energy light sources by dousing it with a second light that primed it like water on a pump.
The result is a photodiode that is not only far more sensitive electromagnetic radiation beyond the visible spectrum, but one that can be tuned to detect more than one wavelength depending on the amount and intensity of light being added.
Semiconductor-based optical detectors go off when light of the right wavelength hits the surface of the semiconductor, exciting electrons on the surface, and creating a tiny electrical field.
Light that is the wrong frequency won't excite enough electrons to set off the detector -- but the determining factor is the material from which the semiconductor is made, not another characteristic that can be easily changed.
Each semiconductor material has its own characteristic structure of bandgaps -- wavelengths of electromagnetic radiation that won't set off the detector because they don't deliver the right among of energy in the right way.
That makes the detectors stable, but makes it very difficult to change the semiconductor to react to a different wavelength without changing the material in the semiconductor itself.
A team led by Unil Perera, a professor of physics at Georgia State University, modified a detector that could only detect light at a very-low 4-micrometer wavelength by adding a light that raised the level of activity to the point that it was able to detect light in the 55-micrometer range, according to an statement from Georgia State University announcing that the paper describing the experiment had been published in the journal Nature Photonics.
The result is an optoelectronic photodetector able to detect a far wider range of light than before, and which can be tuned by changing the secondary light source to detect a wavelength chosen by researchers.
"This technology will also allow dual or multiband detectors to be developed, which could be used to reduce false positives in identifying, for example, toxic gases," according to Perera.
It could also, however, be used to create solar power cells able to absorb and convert to electricity both visible sunlight and infrared energy, allowing it to generate electricity on a cloudy day; for example, sunlight produces heat but little light.
According to computer models and simulations run by the team, the tweaked detector could spot wavelengths as long as 100 micrometers, according to the paper.
“This is a really exciting breakthrough and opens up the opportunity to explore a wide range of new device concepts including more efficient photovoltaics and photodetectors," according to Edmund Linfield, professor of terahertz electronics at the University of Leeds, whose lab built the semiconductors used in the experiment.