UV LED substrate material comparison: Sapphire, Silicon, Aluminum Nitride, Silicon Carbide, Gallium

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Russian president demanded that exports of Russian gas to "unfriendly" countries be settled in rubles. The demand has raised concerns in Germany about possible supply disruptions and the impact on industry and households if utilities do not pay in robles. Europe gets about 40% of its gas from Russia. Last year, Europe imported about 155 billion cubic meters. Germany, Europe's largest economy, depends heavily on Russian gas.

The chief executive of Germany's E.ON said the German economy would face "significant damage, which should be avoided if possible" without Russian supplies. He also said it would take Germany three years to wean itself off Russian gas.  

In the event of a supply disruption, Germany's gas network regulator would prioritize home heating over industrial use, so energy-hungry manufacturers such as steelmakers would be the first to suffer, he said.

The volatile international situations will continue to affect the markets and prices of many commodities like the AlN powder.

The selection of substrate material plays an important role in the epitaxial quality of UV LED. Considering the similar crystal structure, lattice mismatch, and small difference in thermal expansion coefficient, UV LED substrates usually use sapphire (Al2O3) substrate, silicon (Si) substrate, aluminum nitride (AlN) substrate, silicon carbide (6H-sic) substrate, and gallium nitride (GaN) substrate.
 
Sapphire substrate
Sapphire substrate is the mainstream UV LED substrate, with good light transmittance, high-temperature resistance, corrosion resistance, product commercialization maturity (2 inches, 4 inches, 6 inches), and other characteristics.
Although both the sapphire substrate and AlGaN exist certain lattice mismatch and thermal mismatch, which will produce certain defects in the epitaxial layer, and affect the uniformity of crystal growth, they are the six-party symmetric structure, especially for UV transmittance of the sapphire substrate is very high and the price is low, and its electrical and thermal conductivity difference problem can be overcome by flip-chip technology.
Graphical sapphire substrate surface, especially nano graphical sapphire substrate (NPSS), due to the effect by lateral epitaxial reduce its AlGaN epitaxial layer of dislocation density, release the extensional stress and improves the quality of the crystal, and modulation chip internal optical transmission path, the light extraction efficiency, and the process difficulty and the cost is moderate,  It is one of the potential technology routes for the future development of high-efficiency UVC LED. 
Driven by the process cost and the requirements of high yield and high uniformity, the substrate specifications of AlGaN-based UV LED chips in the future will give priority to sapphire substrates with larger thickness, larger size, and appropriate bevel Angle. The thicker substrate can effectively alleviate the abnormal warping of epitaxial wafers caused by stress concentration in the process of epitaxial wafers, thus improving the uniformity of epitaxial wafers. The larger size of the substrate can greatly reduce the edge effect and reduce the overall cost of the chip. An appropriate chamfering Angle can improve the surface morphology of the epitaxial layer, or it can be combined with epitaxial technology to form the localization effect of ga-rich carriers in the active region of quantum well, so as to improve the luminescence efficiency.
To sum up, UV LED put forward new requirements for sapphire substrate size, thickness, and bevel Angle, and it will be necessary to improve the existing substrate production process.
 
Silicon substrate 
Silicon substrate has the advantages of low cost, large area, high quality, good conductivity, thermal conductivity, and easy integration, and its preparation process is relatively mature. As the thermal conductivity of silicon is five times that of sapphire, good heat dissipation enables silicon-backed LEDs to have high performance and long life. At the same time, the silicon substrate can achieve non-destructive peeling, and it is easy to prepare UV LED with vertical structure and thin-film structure. However, there is a larger lattice mismatch and thermal stress mismatch between AlGaN material and silicon substrate, resulting in a large number of defects in the epitaxial layer, serious warping, and easy to cause surface cracking. Therefore, AlGaN epitaxial technology has higher requirements. 
 
Aluminum nitride substrate 
Aluminum nitride single crystal substrate has good thermal conductivity, a small lattice mismatch between it and AlGaN material with high Al component, and low defect density during epitaxial growth. It is an ideal substrate material for preparing HIGH current, high power, and long life UVC LED chips and deep ULTRAVIOLET lasers. Physical gas-phase transport (PVT) is one of the most effective methods to prepare AlN single-crystal substrates. Research on PVT began in the 1960s, but there are still many technical problems, such as cost, size, transmittance, and so on, and the supply is very limited.  Internationally, Crystal IS and Nitride Crystals have mastered the core technology of PVT and can mass-produce 2-inch AlN single Crystal substrates. It is expected that the application of aluminum nitride single crystal growth technology will be limited to high-end fields such as industrial-grade high-power UVC LED, UVC LED below 250 nm, and deep ULTRAVIOLET laser before a breakthrough is made. 
 
Silicon carbide substrate
Silicon carbide and AlGaN lattice mismatch and thermal mismatch are small, and it has excellent conductive and heat conduction characteristics, although after the epitaxial micro-cracks may still happen, the defect density decreased significantly, improving the efficiency and prolonging the service life of LED, and preparation into the vertical or thin-film devices, preparation of AlGaN denotation material and devices is a better candidate substrate. However, silicon carbide substrate has strong absorption of UV light, relatively high material, manufacturing costs, and patent process that requires licensing fees, which are important factors limiting its development in UV LED devices. Commercial silicon carbide substrates are currently priced at a high cost with a maximum size of 6 inches. 
 
Gallium nitride substrate
Gallium nitride single crystal substrate has good conductivity and thermal conductivity, and the lattice mismatch between it and low Al component AlGaN material is small, which can effectively reduce the high defect density caused by the heterogeneous substrate, thus improving the epitaxial crystal quality and improving the device performance and service life of LED and laser diode in near-ultraviolet band. At present, domestic enterprises have been able to produce 2-inch gallium nitride substrates in small batches, with 4-inch substrate production capacity, and developed 6-inch substrate samples, with a typical dislocation density of 106cm-2 magnitude. However, the price of gallium nitride substrate is still high, and its application potential in near-ultraviolet UV LED is limited. 
 
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Due to the limited total amount of traditional energy, people have a huge demand for cleaner and greener new energy alternatives. Now, the emergence of graphene is unlocking the possibility of its application in the energy field, which can create a greener, more efficient, and sustainable future. Here Francesco Bonaccorso, Deputy Director of Innovation at the Graphene Flagship Program, explains how his researchers have developed a series of initiatives to bring graphene from the lab to the commercial market. Graphene has become a research hotspot for new materials in the 21st century. Graphene has been adopted by many industries, the most notable of which are healthcare and key material applications.

The development of graphene has brought huge fluctuations in the demand for AlN powder, and the demand for AlN powder will continue to grow in the future. You can contact us for the latest news on AlN powder.

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