The terahertz part of the electromagnetic spectrum lies between microwaves and the mid-infrared. It remains largely unexplored because it is difficult to make compact, solid-state emitters and detectors that operate in this region.
Now, Aimin Song of the University of Manchester and colleagues at the FELIX Free Electron Laser Facility in Nieuwegein have fabricated a novel asymmetric-nanochannel device that can operate at frequencies of up to 2.5 THz at temperatures as high as 150 K.
Asymmetric geometry
The scientists made their diode using electron-beam nanolithography. Any diode is based on some form of asymmetry. For example, conventional diodes are based on either an asymmetric doping profile or an asymmetric energy barrier. But Song and co-workers are the first to exploit asymmetric geometry.
"The electrons in the surrounding regions of our device channel are either accumulated or depleted depending on the sign of the applied voltage, which automatically switches the nanochannel on or off by electrostatic effects," explained Song. "This leads to diode functionality but the working principle is entirely different from conventional diodes."
The diode is the first electronic nanodevice to work at such a high frequency.
Song says the device, if made at room temperature, will enable compact terahertz detection systems for use in security applications, detecting bioparticles, and even in astrophysics (98% of all of the photons of light emitted since the Big Bang have wavelengths in the terahertz region). The planar architecture of the device also means that it is extremely simple to fabricate an array of such nanodetectors for terahertz imaging – similar to those in normal digital cameras but for terahertz waves.
The team now plans to reduce the size of its device by a factor of two and so hopefully achieve terahertz operation at room temperature.
The researchers reported their work in J. Phys.: Condens. Matter.