Infrared photoelectric detection plays a crucial role in various applications such as spectroscopy, night vision monitoring, infrared guidance, and optical communication. With the advancement of CMOS technology, silicon-based optoelectronic devices have become widely used. However, the large bandgap of silicon (approximately 1.1 eV) limits its effectiveness in detecting near-infrared light beyond 1200 nm. To overcome this limitation, scientists have explored methods like forming Schottky junctions by depositing thin metal films on silicon surfaces.
In this approach, free electrons in the metal absorb photon energy and tunnel through the Schottky barrier into the silicon, generating a photocurrent. The cutoff wavelength is determined by the barrier height, which allows detection beyond the semiconductor's bandgap. Metal nanostructures, such as nanorods, nanowires, and gratings, have been used to enhance performance through mechanisms like surface plasmon resonance. However, these structures often suffer from low quantum efficiency and high manufacturing costs, limiting their scalability.
Recently, researchers from the Suzhou Institute of Nanotechnology and Nano-Bionics, Chinese Academy of Sciences, and Southeast University made significant progress in developing low-cost, high-efficiency silicon-based thermal electron infrared photodetectors. They proposed a gold nanoparticle-modified silicon pyramid structure. Their experiments showed that the device’s performance can rival expensive, well-designed silicon-based near-infrared detectors, making it suitable for large-scale applications in thermal photovoltaics and cost-effective infrared sensing.
The fabrication process was straightforward: using anisotropic wet etching to create pyramids, followed by sputtering a gold layer and forming gold nanoparticles via rapid thermal annealing. An ITO film was deposited on one side, while aluminum served as the back electrode. The sample was then soldered onto a chip carrier using indium tin. The pyramid structure enhanced the coupling between incident photons and gold nanoparticles, reducing back reflection and increasing photon interaction time within the nanoparticles. This boosted the local electromagnetic field, leading to improved light absorption and photoelectric conversion efficiency.
The researchers also utilized a gold nanoparticle-medium-gold mirror structure, combining broadband optical absorption with an omnidirectional Schottky junction (Au/TiO2/Si). This design enhanced both internal and external quantum efficiencies. The random distribution of gold nanoparticles increased light absorption and thermal electron emission, resulting in one of the highest photoelectric responses reported. The cutoff wavelength extended up to nearly 2 micrometers, demonstrating effective near-infrared detection in silicon-based systems.
Through time-resolved IV tests, they analyzed the relationship between the photoelectric effect and the photothermal process, revealing previously overlooked parasitic effects. The study, published in *Laser & Photonics Reviews*, highlights the potential of surface plasmon-enhanced thermal electron emission for applications in photoelectric conversion, photocatalysis, and optical sensing.
This research was supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences.
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