May 22 2025 -- A recent study published in Sensors introduces a new high-speed, broadband photodiode that can detect wavelengths across the critical 850–1550 nm range. This research, developed by a team from the Changchun Institute of Optics, Fine Mechanics, and Physics, Chinese Academy of Sciences, marks a step forward for optical sensing and communication systems. The research presents a device that could simplify multi-wavelength optical systems and improve performance in a variety of applications, including broadband photonic sensors, high-speed communication platforms, and advanced sensing technologies.

The new photodiode uses an innovative combination of InGaAs/InP material systems along with InGaAsP graded bandgap layers (GBLs), designed to reduce material defects that often degrade device performance. By replacing traditional GaAs-based materials with InGaAs, the device improves both speed and efficiency, providing a much-needed upgrade for optical systems that require high sensitivity and fast response times. The device achieves an impressive 20 GHz bandwidth at 850 nm, 15 GHz at 1310 nm, and 15.5 GHz at 1550 nm, with responsivities of 0.5 A/W, 0.72 A/W, and 0.64 A/W, respectively.

Traditionally, photodiodes made from GaAs-based materials have been effective at shorter wavelengths but face limitations when detecting longer wavelengths like 1310 nm and 1550 nm. These materials exhibit poor absorption efficiency and slow electron drift at these longer wavelengths. In contrast, the InGaAs/InP system provides a much faster electron drift velocity and improved absorption, making it ideal for broadband photodiodes.

The incorporation of the InGaAsP graded bandgap layers in this new design addresses key challenges related to defects at the material interfaces, which typically cause high absorption losses. By optimizing lattice compatibility with InP substrates, these layers significantly reduce the degradation of device performance. The results of this research demonstrate how subtle material engineering can enable devices to function efficiently across a wide spectrum, from 850 nm to 1550 nm.

To achieve these improvements, the photodiode was fabricated using a series of precise steps. Researchers employed metal–organic chemical vapor deposition to grow epitaxial layers on an InP substrate, followed by photolithography and etching processes to define the device's structure. The photodiode’s active area measures 35 µm in diameter, which enhances its optical coupling, allowing it to support high-speed detection across multiple wavelengths.

The device’s frequency response was tested using a Lightwave component analyzer, and the maximum bandwidth was recorded at 20 GHz at 850 nm. The performance of the photodiode was particularly notable in its ability to handle the various trade-offs between responsivity, speed, and material defects. At 850 nm, for example, the photodiode achieved a higher bandwidth compared to similar devices made with GaAs-based materials, demonstrating its suitability for advanced optical communication systems.

This new photodiode offers several advantages for the next generation of optical systems. It can detect multiple wavelengths without the need for separate photodiodes for each, simplifying system design and reducing costs. This capability is especially beneficial for optical sensing systems used in fields like LiDAR, optical coherence tomography (OCT), and environmental monitoring, where a wide spectral range is essential.
In addition, the photodiode's high-speed performance across the 850–1550 nm range makes it an ideal candidate for high-speed communication platforms, including wavelength-division multiplexing (WDM) systems, where data is transmitted using multiple wavelengths of light.

The development of this high-speed, broadband InGaAs/InP photodiode is an advancement for optical detection systems. The ability to achieve high performance across a broad wavelength range not only improves sensor and communication capabilities but also simplifies system designs by eliminating the need for multiple detectors. As optical sensing technologies continue to evolve, this device could play a crucial role in enabling more efficient and flexible systems for a variety of applications.