High-Performance Photodetectors for Terahertz Applications

Photodetectors operating in the terahertz (THz) frequency band (0.1–10 THz) are pivotal for emerging applications in high-speed wireless communications, non-invasive imaging, spectroscopy and security screening. The key performance metrics—sensitivity, bandwidth and output power—are governed by carrier transit dynamics, material absorption and device integration. Uni-travelling-carrier and modified uni-travelling-carrier architectures have emerged as leading designs, offering rapid carrier extraction and reduced space-charge effects. Hybrid material platforms, combining III–V semiconductors with silicon or silicon-on-insulator substrates, enable high responsivity and ease of photonic integration. Antenna-coupled layouts and on-chip resonant structures further enhance coupling efficiency and directivity. Recent breakthroughs have extended 3 dB bandwidths beyond 200 GHz, achieved milliwatt-level output at sub-THz frequencies and demonstrated responsivities exceeding 0.15 A/W in silicon-germanium systems. These advances are closing the gap between laboratory prototypes and real-world THz links and sensors, driving a new generation of compact, chip-scale terahertz photonic systems with global significance in communications, biomedical diagnostics and industrial inspection.

Research from Nature Portfolio

A high-responsivity vertical-illumination silicon/germanium uni-travelling-carrier photodiode fabricated on a silicon-on-insulator substrate has demonstrated a 50% improvement in responsivity (0.18 A/W at 1.55 µm) through optimised anti-reflection coatings and constructive interference in the absorption layer. By exploiting the refractive-index contrast of the buried oxide and utilising a thin germanium layer, the device overcomes the speed–responsivity trade-off, achieving rapid carrier extraction without sacrificing quantum efficiency. This architecture provides a viable route to compact, pick-and-place compatible receivers for high-bit-rate digital links and microwave photonic systems.

High-Performance Photodetectors for Terahertz Applications publication trend

The graph below shows the total number of articles in high-performance photodetectors for terahertz applications across all publications each year (not limited to Nature Index journals).

Technical terms

Terahertz (THz): The spectral region between microwave and infrared (0.1–10 THz), bridging electronic and photonic technologies.

Uni-Travelling Carrier photodiode (UTC-PD): A photodiode design in which only electrons participate in high-speed transport, reducing space-charge effects and extending bandwidth.

Modified Uni-Travelling Carrier photodiode (MUTC-PD): An advanced UTC-PD structure incorporating a cliff or saturation layer to improve power handling and linearity at high frequencies.

Responsivity: The ratio of photocurrent generated to incident optical power, measured in amperes per watt (A/W).

3 dB Bandwidth: The frequency range over which the photodetector’s response falls to half its peak power, indicating its operational speed limit.

References

1. Circularly Polarized Ultra-Wideband Antenna for Uni-Traveling-Carrier Photodiode Terahertz Source. Sensors (2023).
2. Ultrafast MUTC photodiodes over 200 GHz with high saturation power.. Optics Express (2023).
3. High-responsivity vertical-illumination Si/Ge uni-traveling-carrier photodiodes based on silicon-on-insulator substrate. Scientific Reports (2016).