Room temperature THz sensor for 6G wireless
A research group in Japan has found a new way to detect terahertz waves at room temperature for next generation 6G technology.
The team at Tohoku University developed a plasmonic terahertz (THz) sensor based on an InGaAs-channel high-electron-mobility transistor (HEMT) that operates with high sensitivity at room temperature
THz waves falls between the microwave and infrared portions of the electromagnetic spectrum, typically spanning frequencies from 300GHz to 3THz and the fast and sensitive detection of THz waves at room temperature is challenging for conventional electronic- or photonic-based semiconductor devices.
This is where two-dimensional plasmons come in. In a semiconductor field-effect transistor, there is a two-dimensional electron channel where a collective charge-density quanta made up of two-dimensional plasmons exists. These plasmons are the excited states of electrons exhibiting fluid-like behaviour. The linear rectification effects, originating from these fluid-like behaviour, and the rapid response means they are not constrained by electron transit time, making them a promising means to detect THz waves at room temperature.
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The researchers looked at a asymmetric dual-grating-gate plasmonic terahertz (THz) detector based on an InGaAs-channel high-electron-mobility transistor (HEMT) in the gate-readout configuration and found a new detection mechanism called the “3D rectification effect”.
This is a cooperative effect of the plasmonic nonlinearities in the channel with the diode nonlinearity in the barrier between the InGaAs channel layer and the InAlAs spacer/carrier-supply/barrier layers, resulting in a giant enhancement of the detector sensitivity.
However this comes with an undesired long-tail waveform from the on the temporal pulse photoresponse of the device due to trapping of carriers in the silicon doped carrier-supply layer when they tunnel through the barrier to the gate. These can be eliminated completely by using an inverted HEMT structure.
The sensor has an internal current responsivity and noise-equivalent power of 0.49 A/W (with the equivalent voltage responsivity of 4.9 kV/W with a high output impedance of 10 kΩ) and 196 pW/√Hz at 0.8 THz.
“We discovered a 3D plasmonic rectification effect in THz wave detector,” says Akira Satou, leader of the research group and associate professor at Tohoku University’s Research Institute for Electrical Communication (RIEC). “The detector was based on an indium-phosphide high-electron mobility transistor and it enabled us to enhance the detection sensitivity more than one order of magnitude higher than conventional detectors based on 2D plasmons.”
The new detection method combined the traditional vertical hydrodynamic nonlinear rectification effect of 2D plasmons with the addition of a vertical diode-current nonlinearity.
It also dramatically resolved the waveform distortion caused by multiple reflections of high-speed modulated signals – a critical issue in conventional detectors based on 2D plasmons.
Leading the group alongside Satou was Specially Appointed Professor Tetsuya Suemitsu from Tohoku University’s New Industry Creation Hatchery Center and Hiroaki Minamide from RIKEN Center for Advanced Photonics.
“Our new detection mechanism overcomes most of the bottlenecks in conventional terahertz-wave detectors,” adds Satou. “Looking ahead, we hope to build on our achievement by improving the device performance.”
These results pave the way towards the application of the plasmonic THz detectors to beyond-5G THz wireless communication systems he says.
10.1515/nanoph-2023-0256; www.otsuji.riec.tohoku.ac.jp/english/index_en.php
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