Objective Terahertz radiation, which lies between microwaves and infrared in the electromagnetic spectrum, combines the penetration ability of microwaves with the high resolution of optical waves. This unique spectral position endows terahertz radiation with enormous potential for applications across various fields such as biomedical imaging, national security surveillance, next-generation wireless communication and non-destructive testing. The terahertz detector is the core component of a terahertz detection system, responsible for transforming terahertz radiation into electrical signals. Existing terahertz detection technologies suffer from high costs, slow response times, dependency on low-temperature conditions and high power consumption. To overcome these challenges, the development of a room-temperature terahertz detector that is highly sensitive, rapidly responsive and energy-efficient has become imperative. The study presented introduces a heterostructure terahertz detector based on a novel topological magnetic insulator, MnBi₂Te₄, and graphene. By exploiting the photothermoelectric effect, the detector achieves high sensitivity, swift response, and low power consumption at room temperature.

Methods Ultraviolet lithography was first employed to create electrode structures on an intrinsic silicon substrate (ρ>10000 Ω·cm), followed by the deposition of 10 nm of titanium (Ti) and 50 nm of gold (Au) via electron beam evaporation. After the metal electrodes were fabricated using a lift-off process, graphene and MnBi₂Te₄ flakes were exfoliated by mechanical exfoliation and subsequently transferred onto the metal electrodes in sequence through a dry transfer method. In this design, the metal electrodes functioned both as conduits for electric current and as antennas for the efficient coupling of terahertz waves. When terahertz radiation was incident on the bow-tie antenna, a significant enhancement in the light absorption efficiency within the device channel was observed. For this reason, the geometric parameters of the bow-tie antenna were simulated and optimized for a terahertz source with a central frequency of 0.12 THz using the finite-difference time-domain method. After the fabrication was completed, the photovoltaic response of the heterostructure device was tested under room temperature and atmospheric conditions. The terahertz response current was amplified by a preamplifier and finally read out with a lock-in amplifier.

Results and Discussions At room temperature, the terahertz detector based on graphene and the magnetic topological insulator MnBi₂Te₄ demonstrated an ultrafast photoelectric response time of 16 μs (as seen in Fig.2(c)) at frequencies of 0.04 THz and 0.12 THz, with responsivities reaching up to 0.43 mA/W and 14.37 mA/W (as shown in Fig.3), along with a comparatively low noise-equivalent power. The detector operates on the principle of thermally exciting the carriers within the graphene-MnBi₂Te₄ heterojunction due to incident terahertz radiation. The differences in thermal conductivity, light absorption, and the Seebeck coefficient between the two materials create a temperature gradient that drives the carriers to move, forming a thermoelectric potential difference and effectively converting terahertz radiation into an electrical signal. The imaging results obtained from the terahertz imaging system constructed in the laboratory (as shown in Fig.5(c)) validate the performance of the detector when integrated into the system.

Conclusions In this study, a heterostructure of graphene and MnBi₂Te₄ was designed to harness the synergistic effects arising from the combination of these two materials. Based on the photothermoelectric effect, the detector exhibited exceptional terahertz detection capabilities in a self-driven mode without the need for an external bias. At room temperature, the device demonstrated high responsivity, ultra-short photoresponse times, and lower noise-equivalent power at frequencies of 0.04 THz and 0.12 THz. These findings suggest that the heterojunction devices composed of the magnetic topological insulator MnBi₂Te₄ and graphene hold significant potential for development in the field of terahertz detection.