Infrared photoelectric detection plays a crucial role in various applications, including spectroscopy, night vision monitoring, infrared guidance, and optical communication. In recent years, the advancement of CMOS technology has enabled widespread use of silicon-based optoelectronic devices. However, due to the wide bandgap of silicon (Si), conventional silicon photodetectors typically fail to operate efficiently beyond 1200 nm in the near-infrared region.
To overcome this limitation, scientists have explored methods such as creating Schottky junctions by depositing thin metal films on silicon surfaces. This allows free electrons in the metal to absorb photon energy and tunnel through the Schottky barrier into the silicon, generating a photocurrent. The cutoff wavelength of this response is determined by the barrier height, which surpasses the semiconductor's bandgap limitations. The performance of these devices is heavily influenced by the metal nanostructures used, such as nanorods, nanowires, and gratings, which enhance the photoelectric response through mechanisms like surface plasmon resonance. Despite these advances, the quantum efficiency remains low, and the fabrication of such fine structures increases production complexity and cost, hindering large-scale and affordable manufacturing.
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 introduced a gold (Au) nanoparticle-modified silicon pyramid structure. Experimental results showed that these devices can match the performance of expensive, well-designed silicon-based near-infrared detectors, making them suitable for large-scale applications in thermal photovoltaic cells and low-cost infrared sensing. The study was published in *Nanotechnology*.
The fabrication process is straightforward: using anisotropic chemical etching to create silicon pyramids, sputtering a gold film on the surface, forming gold nanoparticles via rapid thermal annealing, and depositing ITO and aluminum layers for electrical contact. The detector was assembled using indium tin soldering. The pyramid structure enhances light coupling with gold nanoparticles by reducing back-reflection and increasing photon interaction within the nanoparticles. This leads to stronger local electromagnetic fields and improved light absorption, significantly boosting the photoelectric conversion efficiency.
The team also utilized a gold nanoparticle-medium-gold mirror structure, combining broadband optical absorption with an omnidirectional Schottky junction (Au/TiO₂/Si). This design improves both internal and external quantum efficiency. The random distribution of gold nanoparticles enhances light absorption and thermal electron emission, resulting in one of the highest photoelectric responses reported. The device’s cutoff wavelength extends up to nearly 2 micrometers, demonstrating effective near-infrared silicon-based photoelectric applications.
Through time-resolved IV tests, the researchers analyzed the relationship between photoelectron effects and photothermal processes, revealing the overlooked parasitic photothermal emission. Surface plasmon-enhanced thermal electron emission offers new insights for applications in photoelectric conversion, photocatalysis, and optical sensing. The findings were published in *Laser & Photonics Reviews*.
This research was supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences.
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