Advantages of LED and its industry classification and scope

LED是通电时可发光的半导体材料制成的发光元件，材料使用III-V族化学元素（如：磷化鎵(GaP)、砷化鎵(GaAs)等），发光原理是将电能转换为光，也就是对化合物半导体施加电流，透过电子与电洞的结合，过剩的能量会以光的形式释出，达成发光的效果，属于冷性发光。

LED最大的特点在于：无须暖灯时间(idlingtime)、反应速度很快(约在10^-9秒)、体积小、用电省、污染低、适合量产，具高可靠度，容易配合应用上的需要制成极小或阵列式的元件，适用范围颇广，如汽车、通讯产业、电脑、交通号誌灯、液晶面板用背光源、LED屏幕等。

LED产业主要可以分成上、中、下游三类。上游为单芯片及其外延，中游为LED芯片加工，下游为封装测试以及应用。其中，上游和中游技术含量较高，资本投入密度大。从上游到下游，产品在外观上差距相当大。LED发光顏色与亮度由磊晶材料决定，且磊晶占LED制造成本70%左右，对LED产业极为重要。

The upstream is formed by epitaxy chips, which are roughly a circle with a diameter of six to eight centimeters and are quite thin, like a flat metal. Common epitaxy methods include liquid phase epitaxy (LPE), vapor phase epitaxy (VPE), and metal organic chemical vapor deposition (MOCVD). VPE and LPE technologies are quite mature and can be used to grow general brightness LEDs. The MOCVD method must be used to grow high brightness LEDs. The upstream epitaxy process sequence is: single chip (III-V substrate), structural design, crystal growth, material properties/thickness measurement.

中游厂商根据LED的性能需求进行器件结构和工艺设计，通过外延片扩散、然后金属镀膜，再进行光刻、热处理、形成金属电极，接着将基板磨薄拋光后进行切割。依照芯片的大小，可以切割为二万到四万个芯片。这些芯片长得像沙滩上的沙子一样，通常用特殊胶带固定之后，再送到下游厂商作封装处理。中游芯片制程顺序为：磊芯片、金属膜蒸镀、光罩、蚀刻、热处理、切割、崩裂、测量。

Downstream includes packaging, testing and application of LED chips. LED packaging refers to connecting external leads to the electrodes of LED chips to form LED devices. Packaging plays a role in protecting LED chips and improving light extraction efficiency. The packaging processing sequence of downstream manufacturers is: chip, die bonding, bonding, wire bonding, resin packaging, long baking, tinning, pin cutting, and testing.