碳化硅襯底的LED亮度提高

　　當代LED大部分是由一個組合的氮化銦鎵（InGaN）和藍寶石襯底。建筑作品，使得LED制造商提供150 lm/W，然而過量的參展功效產品，建筑也有一些缺點，鼓勵芯片制造商尋求其他選擇。

　　一個商業上成功的替代品是碳化硅（SiC），基于襯底的LED已經上市兩年了。現在，新一代的技術已經發布，承諾將亮度提高一倍，目前最亮的單LED和削減照明燈具成本百分之40。

　　本文著眼于SiC技術，并介紹了最新的芯片材料的基礎上，看看他們如何與上一代和當代藍寶石基板LED比較。

　　Manufacturing challenges

　　InGaN is the material of choice for the manufacture of today’s high-brightness white LEDs. The bandgap of the semiconductor is carefully manipulated such that the LED die emits blue photons， the majority of which are absorbed by the LED’s phosphor coating and re-emitted in the yellow part of the spectrum. The mixing of blue and yellow light produces a good approximation of white light.

　　Unfortunately， unlike the silicon used for most integrated circuits –– which can be cheaply produced leading to low-cost components –– InGaN is difficult to manufacture in large ingots. LED makers overcome this difficulty by using an epitaxial technique such as metalorganic-chemical-vapor deposition （MOCVD）。 This process overcomes the need to grow bulk InGaN， instead building up the material by depositing successive thin films on a suitable substrate.

　　The most common material for the substrate is sapphire （Al2O3）。 The mineral is cheap， durable， and a good insulator. Figure 1 shows a cross section of a sapphire-substrate LED.