According to the official website of the Moscow Institute of Physics and Technology (MIPT), Russia, a team of scientists from Russia, the United Kingdom, Japan, and Italy has developed a graphene-based terahertz detector. The new device can be used both as a sensitive detector and as a spectrometer operating in the terahertz range.
Terahertz waves are electromagnetic waves between microwaves and infrared rays. They have the advantages of strong penetrability, high security, and good directivity. They are expected to be used in medical and space exploration fields. However, the existing terahertz detector has a problem of low efficiency, mainly due to the size mismatch between the terahertz wave and the detection element (transistor). The transistor is only one millionth of a meter, and the wavelength of terahertz radiation is 100 times its wavelength, causing the terahertz wave to slip away from the detector.
In 1996, scientists proposed a solution: compress the incident wave energy into a volume comparable to the size of a detector. To this end, the detector material needs to support special "compact waves"-so-called plasmons. Theoretically, under the resonance of waves, the efficiency of such a detector will be further improved.
But implementing such a detector is more difficult than expected. The reason is that in most semiconductor materials, plasmons decay rapidly due to the collision of electrons and impurities. Graphene is considered to solve the problem, but it is not clean enough.
In the latest research, scientists have solved this problem. They made a photodetector consisting of a double layer of graphene encapsulated between boron nitride crystals and coupled with a terahertz antenna. In this "sandwich" structure, impurities are expelled from the graphene sheet, allowing the plasmon to spread more freely. Graphene sheets bound by metal lead form a plasmon resonator, and the double-layer structure of graphene allows the wave speed to be tuned over a wide range.
The new device is actually a terahertz spectrometer with a size of only a few micrometers, which can control the resonance frequency through voltage tuning. In addition, it can be used for basic research: measuring the current in the detector at different frequencies and electron densities, showing the characteristics of plasmons.
One of the co-authors of the dissertation and head of the 2D Materials Laboratory at the Moscow Institute of Physics and Technology, said Domitry Sventesfer: "All these devices were available before, but we packed the same functionality into more than ten cubic micrometers. In volume. "