Dear friends, I am "black silicon". Why is it called black silicon? To put it simply, I am also a member of the silicon family, but compared to other conventional silicon brothers, my surface looks very dark, barely reflects light and has a high rate of light absorption. People feel that I can do it naturally. Into a particularly magical device, so give me the name "black silicon." Due to the numerous methods of making me, the understanding of the various branches of semiconductors is not exactly the same. Here I will introduce myself briefly. Please join us in the future and study more and make me more famous.
In the 1980s, some people first produced me by reactive ion etching of silicon substrates (Fig. 1). The so-called reactive ion etching is to etch the silicon surface by bombardment with reactive ion gas after plasma strengthening. It is this high-energy gas ion that is continuously etched on the surface of the silicon, and finally forms a surface structure of a nano-fine needle array on the surface of the silicon. This fine needle can reach a height of more than 10 microns and a diameter of less than 1 micron. The material has a unique performance compared to silicon, so I named it "black silicon." My production is the portrayal of the ancient language cloud "iron smashing into a needle", you see the bombardment of hundreds of millions of high-energy ions, can make my micro-nano-cone surface. After many years, nano research has been surging, and people who have created tides have created a variety of methods to manufacture me. In addition to the improved reactive ion etching methods, there are electrochemical etching, stress etching, vapor phase chemical etching, and metal. Auxiliary chemical etching, plasma immersion etching and many other methods. Although these methods are different, the micro-nano structure seems to be somewhat different, but I can definitely see that I am black enough and use the detector I made. Thermal imaging devices, terahertz applications, solar cells, etc. all have good results. For this reason, people have written a lot of articles for me to discuss my preparation, performance and devices, such as a recent energy source. There is an article in environmental science that introduces my application in solar energy.
Figure 1 Black silicon formed by reactive ion etching
However, people find that I am not really black enough, because the human eye is in the visible light band, and the human eye is not necessarily completely black. For some infrared imaging devices, I am still not black silicon, they can see me through me. Something on the back (Figure 2). Why can I still see through infrared imaging equipment? Because my body is silicon, the band gap of silicon is 1.12 eV. Pure, she can't block the light with wavelength above 1.1 microns, and still pass through. My silicon sister is born like this, how can I become able to absorb infrared light? Before and after 1998, Professor Mazur's group of Harvard University used femtosecond laser to irradiate silicon in sulfur hexafluoride atmosphere, and also incorporated sulfur into the scan while forming a layer of supersaturated doping. Sulfur-based silicon material, the impurity introduced by this silicon material forms a new energy band structure, and a staircase is added between the room and the roof. The long-wavelength photons that could not jump up can now find the stairs, so it is larger than 1.1 microns. The light is also absorbed, so that even the infrared camera can't see the pattern behind me (see Figure 3). Chinese scientists gave me a nice name called broad-spectrum absorption of black silicon. My new feature is capable of absorbing full-spectrum solar energy. The spectrum of sunlight reaching the Earth (Figure 4) is a relatively long spectrum. Typical lines can range from 0.2 microns to 3 microns, while pure crystalline silicon can only absorb wavelengths less than Part of the 1.1 micron light, and a large part of the sun is not in this range, since it can not be absorbed, these lights can not be converted into electricity, and most of the solar energy is wasted. However, I can absorb all of this light, because in addition to the surface micro-nano structure gives me super strong anti-reverse ability, so that I can absorb light less than 1.1 microns, super-saturated sulfur doping also gave me super Strong absorption of light greater than 1.1 micron band, so I can absorb the light of the entire spectrum of the sun. However, can I get satisfactory power with all-black absorption of sunlight?
Figure 2: Black silicon produced by reactive ion etching, visible-light imaging (left) and infrared imaging (right)
Figure 3. Black silicon made by femtosecond laser, visible-light imaging (left) and infrared imaging (right)
Figure 4: Absorption spectrum characteristics of the solar spectrum and silicon (green label)
Modern solar cells began in 1954 and have been 60 years old today. The material at that time was my silicon sister. Today she has made the most widely used battery type in the world, and the factory is constantly producing it, providing a lot of electricity for human beings and benefiting all mankind. And I am still groping in the dark, although many people have a special liking for me because of my blackness, constantly exploring my characteristics. However, everything in the world needs to be optimized in balance. Although the surface micro-nano structure and sulfur doping give me all the blackness, I can keep all the sunlight, but now it is difficult to export the light to make it available. Electricity, because of the micro-nano-amorphous defects caused by lasers, also introduced more electronic composite losses, just like there are too many cars on the road and too many obstacles to block, it is difficult to be smooth. At present, the amount of electricity generated by the infrared sunlight that I absorb more than 1.1 micrometers is almost undetectable, and the photogenerated carriers smaller than 1.1 micrometers have no effect. In order to achieve a smooth path, people have envisaged some paths, in which a path is called the intermediate band (such as the middle band energy level diagram in Figure 5), by holding the normal upper and lower energy level positions and inserting a middle in the middle. The new energy belt is like a new suspended viaduct, so I might be able to use it to generate electricity. But now everyone has not built this bridge.
The solar cell has gradually become a major energy source. The silicon girl has undergone a cultivation of a child to achieve today's achievements. I am almost black for 20 years. Everyone is working hard, and I will build a good bridge and let me absorb it. Light is exported to form more electricity. Let the darkness give me light, I am black silicon, and I am always ready to welcome the sun's radiance.