Quantum Dot THz Detector Developed For 6G Communication


Although 6G technology has a communication frequency between 0.1 to 0.28 terahertz, constructing high-performance detectors to detect the frequencies of 6G technology in large areas at ambient temperature is a challenging issue.

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​​​​​​Study: Terahertz Detectors for 6G Technology Using Quantum Dot 3D Concave Convergence Microwheel Arrays. Image Credit: Dmitry Demidovich/Shutterstock.com

In an article recently published in the journal ACS Photonics, researchers fabricated lead sulfide (PbS) quantum dots microwheel array-based terahertz (THz) detector as an improved version of the conventional THz detector with enhanced performance at room temperature.

The microwheel array based on quantum dots was constructed on a thin gallium nitride (GaN)/ silicon (Si) substrate with the engraved periodic wheel. Additionally, concave convergence of the fabricated quantum dots microwheel array improved the interaction between the device and a terahertz wave.

The fabricated microwheel array detector based on quantum dots was tested under the communication frequencies between 0.14 and 0.28 terahertz for 6G technology, and the results showed the current responses between 3.12 and 4.67 amperes per watts.

The quantum dots microwheel array-based detector showed up to nine-fold higher current responsivity than quantum dots film in 6G technology. The detector’s noise equivalent power values ​​for the communication band between 0.14 and 0.28 terahertz in 6G technology were 6.61 x 10–13 and 1.88 × 10-14 watts per square root hertz. The overall results proved the potential of the current method to develop high performance, large-area THz detector based on quantum dots. These detectors served as improved 6G communication equipment in 6G technology at ambient temperature.

6G Technology and Quantum Dots

6G technology has the potential to meet the requirement of global coverage and can be extended from terrestrial communication networks to non-terrestrial networks, thus achieving a space-air-ground-sea integrated communication network. Furthermore, 6G technology enables a new range of smart applications by utilizing heterogeneous networks, large numbers of antennas, wide bandwidths, and service requirements.

Although 6G technologies utilize communication frequencies of 0.12, 0.22, 0.28, and 0.42 THz, high-performing detectors that work in large areas at ambient temperature are unavailable. The current THz detectors for 6G technology are generally micro/nano/millimeter scaled detectors.

The micro/nanosized detectors used for 6G technology are primarily graphene-based nonlinear hall effect (NHE) detectors, bismuth selenide-based, electromagnetic well (EIW) detectors, and aluminum gallium nitride (AlGaN)/ gallium nitride (GaN). While, millimeter-scale detectors used in 6G technology are thermal-based, including bolometers and Golay cells, with poor performance than nano/microscaled detectors in terms of equivalent noise power and photoresponsivity at room temperature.

Due to the band gap tunability in wide energy range, low cost, and high light absorption coefficients, semiconductor colloidal quantum dots are used in optoelectronic devices. PbS quantum dots have strong quantum confinement and small optical band gaps and are hence used as photodetectors.

Moreover, materials based on quantum dots have unique properties such as tunable absorption band gap, convenient physical size, low crosstalk, low dark current, and solution-based processing for easy device integration. Hence, the incorporation of materials based on quantum dots into the THz imaging chip research results in cost-effective detectors.

6G Technology Using Quantum Dots

In the present study, colloidal quantum dots were used as the active layer to fabricate a 3D microstructure array to introduce the surface plasmon polariton (SPP) effect to enhance the limiting effect on the THz field. This fabrication improved the THz detector’s performance in 6G technology.

The converging THz wave concave structure design resulted in low equivalent noise power and the high response of the constructed device.

The introduction of SPP via 3D quantum dots microwheel array resulted in the gaining of kinetic energy carried by localized carriers, transferred by THz waves due to resonance. Compared to the device without a 3D sub-wavelength structure, the one with that structure improved free carrier concentration and reduced the THz transmission, causing modulation depth of approximately 50% by light.

Testing the detector based on quantum dots for 6G technology with communication frequencies between 0.14 and 0.28 terahertz showed current responses between 3.12 and 4.67 amperes per watt due to the enhancement in SPP. The quantum dots microwheel array-based detector exhibited better noise equivalent power (NEP) of 1.88 x 10-14 watts per square root hertz compared to other millimeter detectors used in 6G technology.

Conclusion

To summarize, the performance of the THz detector based on the quantum dots microwheel array was demonstrated. The low crosstalk and small dark current of colloidal quantum dots were advantageous to improving the THz detector’s performance in 6G technology, hence were used as the active layer to construct a 3D microstructure array

The 3D microstructure array introduced the SPP effect and improved the THz field’s limiting effect. Combining the enhanced limiting effect of the THz field and the converging THz wave’s concave structure resulted in low equivalent noise power and high response.

Reference

Song, Q., Xu, Y., Zhou, Z., Liang, H., Zhang, M., Zhu, G., Yang, J et al. (2022). Terahertz Detectors for 6G Technology Using Quantum Dot 3D Concave Convergence Microwheel Arrays. ACS Photonics. https://pubs.acs.org/doi/10.1021/acsphotonics.2c00735

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