Dual-band detector could help put out fires
A detector that it sensitive to both ultraviolet (UV) and near infrared light (NIR) has been developed by a team of researchers led by Georgia State University in the US.
The dual-band detector could supplant cumbersome devices that rely on several of different detectors, all with their separate cooling assemblies and electronics.
"At present, there are either UV detectors or there are IR detectors, so if one needs to detect both, one needs two detectors," said Unil Perera of Georgia State. "But this is a single chip that can detect both."
While dual-band detectors do already exist, hitherto models have solely operated in the IR region. But because this new device has extended one of the bands into the UV, it could open up a new range of applications.
One of these is fire detection. The source of a fire - in other words, its fuel - is an important consideration for fire fighters. The dual-band detector would allow them to determine the nature of the source by scrutinizing the emission spectrum for signature UV patterns.
"Any fire emits infrared," said Perera. "However, based on the source of the fire, they can emit UV radiation too." Two examples would be coal and hydrogen, which emit vastly different intensities at UV and IR wavelengths.
The detector could also be used in the military and forensics, such as checking for blood stains or gunshot residues.
One chip, two mechanisms
The researchers grew the detector by MOCVD on a sapphire substrate, producing an undoped AlGaN barrier sandwiched between an n+ GaN emitter layer and an n+ GaN bottom layer.
It is in this heterostructure that the two different detection mechanisms arise: interband transitions across the AlGaN barrier are stimulated by UV, while intraband transitions in the emitter layer are stimulated by NIR.
By changing the composition of the material, said Perera, the threshold of the interband and intraband transitions can be tailored. "GaN has a large energy gap, and, by using Al, that gap can be engineered.
"The versatility of this method will be to adjust the wavelength of the infrared radiation. If one then uses a material like InGaN, one can also detect visible photons, hence covering the whole range from UV to visible to IR."
Unfortunately, the simultaneous detection of two bands is a little way off. "We need to have simultaneous measurement capability," Perera continued. "Then we will increase the UV efficiency and develop arrays."
