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LED Substrates

LED Substrates

LED remains the dominant sapphire application. Sapphire substrates are ideal for use in LED applications due to high-temperature resistance, high strength, good electrical insulation, and low dielectric loss. Sapphire substrate in LED lighting helps prevent stray currents caused by radiation from spreading to nearby circuit elements. Its crystal structure also allows LED lights to have a wider beam angle.


The Development of Wafers in the Led Industry

In the past, 2 to 4-inch sized wafers were commonplace, but there has been a recent transition towards 6 to 8-inch wafers. Larger sized wafer allows manufactures to incorporate more LED chips along the outside edge, increasing the brightness of the LEDs. The use of patterned sapphire substrate (PSS) can further increase brightness due to the reduction in density of the GaN layer and enhancement of light extraction efficiency. With the penetration rate for LED-based general lighting continuing to rise, large-sized PSS will become necessary to meet the demands of the rapidly growing lighting market.


As the sapphire substrate is still a key building block for LEDs, general lighting is expected to continue providing solid demand for substrate material from the LED industry in the following years.


LED (Light Emitting Diode) has been widely regarded as the main lighting tool of the next generation. Compared with the incandescent lamps currently used, LEDs have the advantages of long life, energy-saving, and safety. The preparation of blue LEDs needs to rely on GaN films. There are many substrate materials used for growing GaN films, such as sapphire and SiC are the most commonly used.


LED Substrates


In recent years, sapphire has become the best and most commonly used substrate material, because of its small lattice mismatch coefficient with GaN and good light transmission. The lattices of the single-crystal sapphire substrate and GaN can match each other, and sapphire has good high-temperature stability and mechanical properties which can meet the requirements of high-temperature resistance during the growth of GaN film.


Moreover, a single-crystal sapphire substrate has better light transmission in the visible range. In addition, there is more research regarding GaN film on sapphire, the production technology of GaN on sapphire is relatively mature and the price is relatively cheap, so single-crystal sapphire has become the key substrate material for making white, blue, green, and blue-green GaN substrates.


Factors Must Be Considered when Evaluating Substrate Materials

1. The degree of structural matching between the substrate and the epitaxial film: the crystal structure of the epitaxial material and the substrate material are the same or similar, the lattice constant mismatch is small, the crystallization performance is good, and the defect density is low.

2. The degree of thermal expansion coefficient matching between the substrate and the epitaxial film. The matching of the thermal expansion coefficient is very important. The thermal expansion coefficient of the epitaxial film and the substrate material is too large and may reduce the quality of the epitaxial film. Therefore, during the device operation, due to heat generation, This can cause device damage.

3. The degree of matching the chemical stability of the substrate and the epitaxial film: the substrate material must have good chemical stability, not be easily decomposed and corroded in the temperature and atmosphere of epitaxial growth, and the quality of the epitaxial film cannot be caused by the chemical reaction with the epitaxial film decline.

4. Difficulty and cost of material preparation: Considering the needs of industrialization development, the preparation of substrate materials requires conciseness, the cost should not be high, and the substrate size is generally not less than 2 inches.


LED Process Introduction (LED Substrates)

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