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LED (Light Emitting Diode) is a solid-state semiconductor device that directly converts electrical energy into light. At its core is a semiconductor wafer, one end of which is connected to the negative terminal, while the other is linked to the positive terminal of the power supply. The entire wafer is then encapsulated in epoxy resin. This semiconductor consists of three main parts: a P-type semiconductor, where holes dominate, an N-type semiconductor, where electrons are the primary charge carriers, and a quantum well located between them, typically consisting of 1 to 5 layers. When current flows through the wafer, electrons and holes are injected into the quantum well, where they recombine and release energy in the form of photons. This process is what enables LED lighting. The color of the emitted light, or its wavelength, depends on the material used in the PN junction.
LEDs are widely used in display systems, capable of showing text, graphics, images, videos, and animations. Their advantages include low-voltage DC operation, high color richness when combined, and long lifespan, making them popular in urban projects and large-screen displays. LEDs can be controlled by computers to show dynamic content with varying colors.
The epitaxial film process for LEDs involves several steps. Over the past decade, significant research has been focused on developing blue and high-brightness LEDs, leading to the commercialization of blue and green LEDs as well as laser diodes. In current LED manufacturing, red and green LEDs often use liquid-phase epitaxy, while yellow and orange LEDs are grown using vapor-phase methods.
Growth of GaN requires high temperatures to break the NH3 bond. During this process, non-volatile by-products may form due to reactions between NH3 and metalorganic gases. The typical epitaxial wafer process includes substrate preparation, buffer layer growth, n-type GaN layer growth, multiple quantum well luminescence layer, p-type GaN layer growth, annealing, and final testing such as photoluminescence and X-ray analysis.
After the epitaxial wafer is produced, it undergoes various processing steps like lithography, ion etching, electrode formation, dicing, and chip sorting. Each stage contributes to the final quality and performance of the LED.
The silicon wafer production process includes slicing, annealing, chamfering, grinding, cleaning, and polishing. These steps ensure the wafers meet strict specifications for further processing. Cleaning techniques such as RCA cleaning involve multiple chemical solutions to remove contaminants, generating waste products like sulfuric acid mist, hydrofluoric acid, and ammonia gas.
Chemical etching is also used to remove surface damage caused by mechanical processes. Different types of corrosion—acidic and alkaline—are applied depending on the requirements. Polishing, both rough and fine, improves the flatness and smoothness of the wafers before final inspection and packaging.
In summary, the LED manufacturing process is complex and involves numerous precise steps to ensure high-quality output. From epitaxial growth to packaging, each stage plays a critical role in determining the performance and reliability of the final product.