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The amazing power of single-crystal silicon: Why it is the building block of modern electronics?
Single crystal silicon, often referred to as single-crystal silicon or simply mono-Si, is a material that is critical in modern electronic devices and photovoltaic technology. As the basis for silicon-based discrete components and integrated circuits, it plays a key role in nearly all modern electronic devices, from computers to smartphones. In addition, single crystal silicon is used as a highly efficient light-absorbing material in the production of solar cells, making it indispensable in the field of renewable energy.
"The crystal lattice of single-crystal silicon is continuous and does not have any grain boundaries."
The properties of single-crystal silicon make it particularly important in semiconductor applications. It can consist of only very high-purity silicon as an intrinsic semiconductor, or it can be doped by adding other elements such as boron or phosphorus to create p-type or n-type silicon. This semiconductor property has made single-crystalline silicon the most important technological material in the past few decades, marking the advent of the "Silicon Age". Its low cost and availability is an important foundation for the development of today's electronic products and information technology revolution.
Single-crystal silicon differs from other allotropic forms, such as amorphous silicon, which is used in thin-film solar cells, and polycrystalline silicon, which is made up of small crystals. These differences determine their different performance and cost.
Production process
Single crystal silicon is typically made through methods that involve melting high-purity, semiconductor-grade silicon and using a seed crystal to initiate the formation of a continuous single crystal. This process is usually performed in an inert atmosphere, such as argon, and in an inert crucible such as quartz to avoid impurities that could affect the homogeneity of the crystal.
"The most common production technology is the Czochralski method, which is capable of producing single-wafer ingots up to 2 meters long and weighing several hundred kilograms."
In the Czochralski method, a precisely oriented rod-shaped seed crystal is dropped into molten silicon and then slowly pulled up and rotated, allowing the pulled material to solidify into a single-crystalline, rounded strip. Magnetic fields may also be applied during this process to control and suppress turbulent flow, further improving the uniformity of the crystal. Other production methods include the zone melt method and the Bridgman technique, which also use heating within a temperature gradient capsule to promote crystal growth.
The solidified round bars are cut into thin wafers and further processed to prepare them for manufacturing. Compared to the casting of multi-wafer ingots, the production process of single-crystal silicon is relatively slow and costly. However, due to its superior electronic properties, the demand for single crystal silicon continues to increase.
Applications in electronics
The main application of single crystal silicon is in the production of discrete components and integrated circuits. The round rods made using the Czochralski method are cut into wafers about 0.75 mm thick, on which microelectronic devices are built using various microprocesses such as doping, ion implantation, etching and thin film deposition.
"A single continuous crystal is crucial for electronics because grain boundaries, impurities and crystal defects can significantly affect the local electronic properties of the material."
Without crystal perfection, it would be nearly impossible to build very large scale integrated circuit (VLSI) devices, which contain billions of transistor circuits that must all operate reliably. For this reason, the electronics industry has invested heavily in facilities to produce large single crystals of silicon.
Application in solar cells
Single-crystal silicon is also used in high-performance photovoltaic devices. Since the requirements for structural defects are not as stringent as those for microelectronic applications, slightly lower quality solar-grade silicon (Sog-Si) is often used to manufacture solar cells. However, the development of the monocrystalline silicon photovoltaic industry has benefited from the rapid progress of monocrystalline silicon production methods in the electronics industry.
Market Share and Efficiency
As the second most common photovoltaic technology, monocrystalline silicon is second only to its sister product, multicrystalline silicon. Despite the faster production of multicrystalline silicon and continued cost reductions, the market share of monocrystalline silicon has been gradually declining since 2013: in that year, the market share of monocrystalline silicon solar cells was 36%, translating into 12.6 GW of PV capacity, but by 2016, the market share of monocrystalline silicon solar cells had risen to 1.35 GW. In 2017, its market share had fallen below 25%.
"The laboratory efficiency of single-crystal silicon single-crystal cells has reached 26.7%, which is the highest conversion efficiency confirmed among all commercial photovoltaic technologies."
The efficiency of monocrystalline silicon photovoltaic modules reached 24.4% in 2016. In some applications, especially where there are restrictions on weight or available area, the high efficiency of monocrystalline silicon solar cells is particularly important.
Manufacturing Challenges and Comparisons
In addition to inefficient productivity, there is also the problem of material waste in the manufacturing process. During the dicing process of round wafers, the material on the left side is often not fully utilized and is either discarded or recycled and remelted. However, technological advances indicate that wafer thickness will be reduced to less than 140μm in the future. Other manufacturing methods, such as direct wafer growth, are also being investigated as new ways to reduce waste in traditional dicing processes.
Single crystal silicon differs significantly from other forms of silicon, such as polycrystalline silicon and amorphous silicon. Polycrystalline silicon is made up of multiple grains and is cheaper to produce but has lower efficiency; amorphous silicon is mainly used in thin-film solar cells. Although it is light and flexible, it is extremely inefficient. The choice of various silicon types has a continuous impact on the technical requirements and economic considerations of different applications.
As technology advances, how to effectively balance cost and efficiency will be a question that needs to be considered in the future development of the photovoltaic and electronics industries.
