Second Light Source Primes Semiconductors to See IR

Traditional semiconductors may just need a little help to see the (IR) light.

A team from the University of Leeds and Georgia State University has developed a new technology that uses standard, patterned semiconductors to detect light over a broader range of wavelengths. Until now, this has proved challenging, as not all semiconductor materials respond to low-energy light.

“Generating electric current from the lower energy ranges of the electromagnetic spectrum, such as IR, is very challenging using semiconductor materials because the wavelengths involved provide little energy,” said Edmund Linfield, a professor of terahertz electronics at the University of Leeds' School of Electronic and Electrical Engineering.

The new technology, for which the researchers have filed a patent application, incorporates a second light source. This prepares the semiconductor with energy in advance, allowing a stronger current to be generated as soon as the low-energy wavelengths arrive.

The technique is based on a “hot-cold hole energy transfer mechanism” that overcomes the spectral limit common to traditional semiconductors. In the study, hot carriers injected into a semiconductor structure were shown to interact with cold carriers and excite them to higher energy states.

This extends the range for existing semiconductors, which offers the potential for wafer-scale integration with electronic devices, the researchers said.

While similar technology in the past has only been able to visualize wavelengths of about 4 µm, this new technology can detect wavelengths down to at least the 55-µm range.

Further studies conducted by the team recently have also shown that a refined version of this new technology could detect wavelengths down to 100 µm.

“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,” said Unil Perera, a professor and head of Georgia State’s Optoelectronics Research Laboratory.

The research was supported by the US Army Research Office, the US National Science Foundation, the UK’s Engineering and Physical Sciences Research Council (EPSRC), and a grant from the European Research Council (TOSCA). The work is published in Nature Photonics. (doi: 10.1038/NPHOTON.2014.80)

For more information, visit: www.leeds.ac.uk