Progress in research on silicon-based near-infrared photoelectric conversion

Infrared photoelectric detection is of great significance for applications such as spectroscopy, nighttime monitoring, infrared guidance, and optical communication. In recent years, the development of CMOS technology has made Si-based optoelectronic devices widely used. Due to the large band gap of silicon (Si), ordinary silicon-based photodetectors are generally unable to work effectively in the near-infrared region exceeding 1200 nm.

In order to solve this problem, scientists deposited a thin film of metal on the surface of silicon material to form a Schottky junction between the metal and the semiconductor. The free electrons in the metal absorb the photon energy and then pass through the Schottky barrier and enter the silicon material. A photocurrent is formed in the middle. The cutoff wavelength of this response is determined by the barrier height, which breaks the limits of the semiconductor bandgap. Under this photoelectric response mechanism relying on thermal electron emission, the metal structure has a great influence on the near-infrared detection performance of the device. At present, various metal nanostructures such as nanorods, nanowires, and gratings have been proven to enhance heat based on, for example, transmission surface plasmon resonance (PSPR), local surface plasmon resonance (LSPR), and cavity resonance. Electronic photoelectric response. However, the quantum efficiency of such structures is still low, and these fine-grained nanostructures increase the complexity of the production process and the production cost, making it impossible to achieve large-scale, low-cost manufacturing.

Recently, Chen Qi, a researcher at the Suzhou Institute of Nanotechnology and Nano-Bionics of the Chinese Academy of Sciences, and Wang Qilong, a professor at Southeast University, have made series progress in low-cost and high-efficiency silicon-based thermal electronic infrared photodetectors. Researchers have proposed a gold (Au) nanoparticle modified silicon pyramid structure. Experiments show that the properties of these devices can be comparable to the well-designed and costly silicon-based near-infrared photodetectors, and are expected to be applied on a large scale. Thermal photovoltaic cells and low-cost infrared detection. Related research results were published on Nanotechnology. The process used by researchers is very simple, using a standard anisotropic chemical wet etching method to achieve the construction of Si-based pyramids; sputtering a layer of gold film on its surface; forming modified gold nanoparticles by rapid thermal annealing; The ITO film was deposited by magnetron sputtering on the pyramid side and the aluminum film was deposited as the back electrode by thermal evaporation on the other side. The sample was soldered to the chip carrier by indium tin to complete the fabrication of the detector (Figs. 1 and 2). They found that the pyramid surface enhances the coupling effect between incident photons and gold nanoparticles, because the pyramid surface reduces back-reflected light and causes photons to be reflected multiple times inside the gold nanoparticles, increasing the distance of incident light, gold nanoparticles. The introduction also increases the local electromagnetic field of the device, so that photons can be significantly absorbed, which improves the photoelectric conversion quantum efficiency.

Fig.1 Schematic diagram and experimental results of the manufacturing process of silicon pyramid decorated with gold nanoparticles

Fig. 2 Silicon-based thermoelectron photodetector with gold nanoparticle-medium-gold mirror structure, energy band structure, optical characterization and experimental SEM image

Figure 3 Photoelectric test analysis results

The researchers used a gold nanoparticle-medium-gold mirror structure to make full use of the broadband high optical absorption of disordered metal nanoparticles and the omnidirectional Schottky junction composed of Au/TiO2/Si, both optically and electrically. At the same time, we will improve the internal and external quantum efficiency of photoelectric conversion. This dense random spot distribution enhances the efficiency of light absorption and thermal electron emission. Photoelectric response is one of the highest results. The silicon photoelectric response cutoff wavelength extends to nearly 2 um, demonstrating an effective near-infrared silicon base. Photoelectric applications. In addition, through time-resolved IV positive and negative bias test analysis, they analyzed the relationship between the photoelectric effect of photoelectron and the photothermal effect in photothermal process, and unveiled the photothermal effect of the parasitic photothermal emission process neglected in previous work. Surface plasmon enhanced thermal electron emission provides an important basis and reference for photoelectric conversion, photocatalysis, and optical sensing applications. The results were published on Laser & Photonics Reviews.

This work was supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences.