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LED (Light Emitting Diode) is a solid-state semiconductor device that directly converts electrical energy into light. At its core, an LED contains a semiconductor wafer, with one end connected to a negative terminal and the other to a positive terminal of the power supply. This wafer is then encapsulated in epoxy resin for protection. The semiconductor is composed of two main parts: a P-type region, where holes dominate, and an N-type region, where electrons are the primary charge carriers. Between them lies a quantum well, typically consisting of 1 to 5 layers. When current flows through the wafer, electrons from the N-type region move toward the P-type region, where they recombine with holes. This recombination releases energy in the form of photons, producing light. The color of the emitted light depends on the material used in the PN junction.
LEDs are widely used in various applications, including display screens that show text, images, animations, and videos. They are favored for their low-voltage operation, long lifespan, and vibrant color performance. Their ability to be controlled by computers makes them ideal for large-screen displays and urban lighting projects.
The production of LED epitaxial wafers involves several key steps. First, a substrate is selected, followed by structural design and the growth of a buffer layer. Then, n-type GaN, multiple quantum well layers, and p-type GaN are sequentially deposited. After annealing and testing using techniques like photoluminescence and X-ray analysis, the epitaxial wafer is ready for further processing.
Next, the wafer undergoes lithography, ion etching, and electrode formation—both n-type and p-type. Following this, the wafer is diced into individual chips, which are then sorted and graded based on performance.
In the manufacturing process, silicon wafers are cut from single crystal rods, cleaned, and polished. Each step, such as slicing, annealing, chamfering, and grinding, contributes to the final quality of the wafer. Cleaning processes, including RCA cleaning with solutions like SPM, DHF, APM, and HPM, ensure the surface is free from contaminants. Chemical etching removes damaged layers, while polishing improves surface flatness.
Finally, the finished wafers are packaged and used in chip fabrication, where they are cut into small LED chips for use in lighting and display systems. This entire process highlights the complexity and precision required to produce high-quality LEDs that power modern technology.