Black-Phosphorus Terahertz Photodetectors (1805.00735v1)

Abstract: The discovery of graphene and the related fascinating capabilities have triggered an unprecedented interest in inorganic two-dimensional (2D) materials. Despite the impressive impact in a variety of photonic applications, the absence of energy gap has hampered its broader applicability in many optoelectronic devices. The recent advance of novel 2D materials, such as transition-metal dichalcogenides or atomically thin elemental materials, (e.g. silicene, germanene and phosphorene) promises a revolutionary step-change. Here we devise the first room-temperature Terahertz (THz) frequency detector exploiting few-layer phosphorene, e.g., a 10 nm thick flake of exfoliated crystalline black phosphorus (BP), as active channel of a field-effect transistor (FET). By exploiting the direct band gap of BP to fully switch between insulating and conducting states and by engineering proper antennas for efficient light harvesting, we reach detection performance comparable with commercial detection technologies, providing the first technological demonstration of a phosphorus-based active THz device.

• The paper demonstrates a BP-based FET photodetector for terahertz radiation, achieving room-temperature operation with mobility over 650 cm²/V·s.
• It leverages black phosphorus's direct bandgap and anisotropic properties to modulate conductivity through plasma wave rectification.
• The study outlines paths for enhancing device stability and sensitivity via improved passivation and optimized antenna design.

Overview of Black-Phosphorus Terahertz Photodetectors

The paper presents the development and characterization of terahertz (THz) photodetectors based on black phosphorus (BP), utilizing its unique electronic properties as a two-dimensional material. These devices represent a significant advancement in the application of 2D materials beyond graphene, particularly in their ability to function at room temperature (RT) and match commercial photodetection technologies in performance.

Key Results

The research documents the fabrication of a field-effect transistor (FET) with a phosphorene channel measuring 10 nm in thickness, resulting in a device capable of detecting THz-frequency radiation. The device benefits from BP's direct bandgap, which facilitates effective modulation of its conductivity between insulating and conducting states. This makes BP-based photodetectors ideal candidates for THz detection, which is primarily reliant on the rectification of plasma waves induced by an external AC electric field. The achieved room-temperature mobility exceeded 650 cm²/V·s, with operational frequency capabilities reaching 20 GHz. Moreover, the paper reports an on/off current ratio (Ion/Ioff) of 10³, showcasing the potential of BP-based devices to outperform traditional TMDCs, despite their higher mobility constraints.

Implications

From a practical viewpoint, these BP-based THz devices could substantially impact technologies operating in the gap between microwave and optical components. The paper's findings also suggest a pathway for developing high-performance, BP-based transistors and optoelectronic devices with optimal bandgaps for transparency and photovoltaic applications. By successfully integrating BP into FETs, the research opens opportunities for further exploiting the anisotropic electronic properties of layered materials to achieve innovative functionalities beyond those possible with isotropic materials like graphene.

Future Directions

Future research is likely to focus on improving the BP devices’ stability under environmental conditions and further refining their sensitivity and spectral range through novel fabrication techniques or hybrid material systems. Specifically, efforts could be directed towards better understanding and mitigating the degradation of BP in air, enhancing its passivation by employing high-k dielectrics, and customizing the design of integrated antenna structures to optimize THz detection.

Overall, the paper provides a compelling demonstration of BP’s applicability in next-generation photodetector technology. With these promising capabilities, BP and similar 2D materials stand poised to revolutionize various optoelectronic and high-frequency electronic applications, marking a significant addition to the material choices available in these fields.