In recent years, low-dimensional semiconductors have attracted widespread attention in the field of next-generation broadband infrared photodetectors due to their tunable band structures, strong light-matter interactions, and compatibility with mixed-dimensional integration. Among them, tellurium (Te) and bismuth selenide (Bi₂O₂Se) have become ideal candidate materials for high-performance detection due to their inherent anisotropy, high carrier mobility, and broad spectral response. Constructing heterojunction photodetectors based on these materials can achieve self-powered operation and suppress dark current. Heterojunction interface engineering and band structure design capabilities are crucial for constructing high-performance Te/Bi₂O₂Se heterojunction photodetectors. Therefore, we in-situ construct a one-dimensional (1D) Te/two-dimensional (2D) Bi₂O₂Se heterojunction by a two-step chemical vapor deposition method, which shown a clear interface and type-II band alignment structure. Therefore, the photodetector based on Te/Bi₂O₂Se heterojunction working in self-driven mode exhibits high performance, showing a high responsivity of ~ 0.89 A·W⁻¹ and a fast response time of ~ 29/41 μs under 1550 nm light irradiation. Further, owing to the optical absorption anisotropy of tellurium, the device exhibited a high polarization ratio of 2.8 and successfully demonstrated polarization optical communication and polarization imaging applications. This work provides new ideas for the in-situ construction strategy of high-quality mixed-dimensional van der Waals heterojunctions and the research on high-performance photodetectors and their applications.

Photoelectric pulse oximeters are widely favored for their non-invasive and continuous monitoring of pulse rate and blood oxygen saturation, which are vital indicators of physiological health. However, traditional pulse oximeters are frequently hindered by several limitations, such as high-power consumption, instability, and reduced precision. Herein, a WSe₂/Si p–n heterojunction photodiode was in-situ fabricated for self-powered high-precision pulse rate and blood oxygen saturation monitoring. Our device demonstrated the excellent broadband photoresponse performance from 265 to 980 nm, covering the biological window, including a high responsivity of 740 mA/W, a fast response time of 7.8/7.1 µs and a low detection limit of 25 nW/cm². Leveraging these prominent photoelectrical properties, the WSe₂/Si photodiode demonstrates high accuracy and reliability in detecting the physiological signals of heart rate and blood oxygen saturation through a triple-wavelength measurement method, with an error margin of less than 1%, thereby validating its accuracy and reliability for non-invasive health monitoring applications. These achievements provide a new approach for developing low-power, high-sensitivity optoelectronic pulse oximeters.

Broadband photodetection, spanning from ultraviolet (UV) to infrared (IR), is pivotal in diverse technological domains including astronomy, remote sensing, environmental monitoring, and medical diagnostics. However, current commercially available broadband photodetectors, predominately based on conventional narrow-bandgap semiconductors, exhibit limited sensitivity in the UV region. This limitation, stemming from the significant energy disparity between the semiconductor bandgap and UV photon, narrows their application scope. Herein, we report an innovative approach involving the in-situ van der Waals (vdW) integration of two-dimensional (2D) GeSe₂ layers onto a Si substrate. This process yields a high-quality GeSe₂/Si vdW heterojunction device, which features a broad response range covering from UV to near-IR (NIR) with a greatly-enhanced sensitivity in the UV region. The device possesses high responsivities of 325 and 533.4 mA/W, large detectivities of 1.24 × 10¹³ and 2.57 × 10¹³ Jones, and fast response speeds of 20.6/82.1 and 17.7/81.0 μs under 360 and 980 nm, respectively. Notably, the broadband image sensing and secure invisible optical communication capabilities of the GeSe₂/Si heterojunction device are demonstrated. Our work provides a viable approach for UV-enhanced broadband photodetection technology, opening up new possibilities and applications across various scientific and technological domains.

High-sensitivity room-temperature multi-dimensional infrared (IR) detection is crucial for military and civilian purposes. Recently, the gapless electronic structures and unique optoelectrical properties have made the two-dimensional (2D) topological semimetals promising candidates for the realization of multifunctional optoelectronic devices. Here, we demonstrated the in-situ construction of high-performance 1T’-MoTe₂/Ge Schottky junction device by inserting an ultrathin AlO_x passivation layer. The good detection performance with an ultra-broadband detection wavelength range of up to 10.6 micron, an ultrafast response time of ~ 160 ns, and a large specific detectivity of over 10⁹ Jones in mid-infrared (MIR) range surpasses that of most 2D materials-based IR sensors, approaching the performance of commercial IR photodiodes. The on-chip integrated device arrays with 64 functional detectors feature high-resolution imaging capability at room temperature. All these outstanding detection features have enabled the demonstration of position-sensitive detection applications. It demonstrates an exceptional position sensitivity of 14.9 mV/mm, an outstanding nonlinearity of 6.44%, and commendable trajectory tracking and optoelectronic demodulation capabilities. This study not only offers a promising route towards room-temperature MIR optoelectronic applications, but also demonstrates a great potential for application in optical sensing systems.

As one of the most promising materials for two-dimensional transition metal chalcogenides (2D TMDs), molybdenum diselenide (MoSe₂) has great potential in photodetectors due to its excellent properties like tunable bandgap, high carrier mobility, and excellent air stability. Although 2D MoSe₂-based photodetectors have been reported to exhibit admired performance, the large-area 2D MoSe₂ layers are difficult to be achieved via conventional synthesis methods, which severely impedes its future applications. Here, we present the controllable growth of large-area 2D MoSe₂ layers over 3.5-inch with excellent homogeneity by a simple post-selenization route. Further, a high-quality n-MoSe₂/p-Si van der Waals (vdW) heterojunction device is in-situ fabricated by directly growing 2D n-MoSe₂ layers on the patterned p-Si substrate, which shows a self-driven broadband photoresponse ranging from ultraviolet to mid-wave infrared with an impressive responsivity of 720.5 mA·W⁻¹, a high specific detectivity of 10¹³ Jones, and a fast response time to follow nanosecond pulsed optical signal. In addition, thanks to the inch-level 2D MoSe₂ layers, a 4 × 4 integrated heterojunction device array is achieved, which has demonstrated good uniformity and satisfying imaging capability. The large-area 2D MoSe₂ layer and its heterojunction device array have great promise for high-performance photodetection and imaging applications in integrated optoelectronic systems.

Two-dimensional (2D) layered materials have been considered promising candidates for next-generation optoelectronics. However, the performance of 2D photodetectors still has much room for improvement due to weak light absorption of planar 2D materials and lack of high-quality heterojunction preparation technology. Notably, 2D materials integrating with mature bulk semiconductors are a promising pathway to overcome this limitation and promote the practical application on optoelectronics. In this work, we present the patterned assembly of MoSe₂/pyramid Si mixed-dimensional van der Waals (vdW) heterojunction arrays for broadband photodetection and imaging. Benefited from the light trapping effect induced enhanced optical absorption and high-quality vdW heterojunction, the photodetector demonstrates a wide spectral response range from 265 to 1550 nm, large responsivity up to 0.67 A·W⁻¹, high specific detectivity of 1.84 × 10¹³ Jones, and ultrafast response time of 0.34/5.6 μs at 0 V. Moreover, the photodetector array exhibits outstanding broadband image sensing capability. This study offers a novel development route for high-performance and broadband photodetector array by MoSe₂/pyramid Si mixed-dimensional heterojunction.

The research of ultraviolet photodetectors (UV PDs) have been attracting extensive attention, due to their important applications in many areas. In this study, PtSe₂/GaN heterojunction is in-situ fabricated by synthesis of large-area vertically standing two-dimensional (2D) PtSe₂ film on n-GaN substrate. The PtSe₂/GaN heterojunction device demonstrates excellent photoresponse properties under illumination by deep UV light of 265 nm at zero bias voltage. Further analysis reveals that a high responsivity of 193 mAdW^-1, an ultrahigh specific detectivity of 3.8 × 10¹⁴ Jones, linear dynamic range of 155 dB and current on/off ratio of ~ 10⁸, as well as fast response speeds of 45/102 njs were obtained at zero bias voltage. Moreover, this device response quickly to the pulse laser of 266 nm with a rise time of 172 ns. Such high-performance PtSe₂/GaN heterojunction UV PD demonstrated in this work is far superior to previously reported results, suggesting that it has great potential for deep UV detection.