材料和制造改進提高LED效率

　　從理論上說，制造高亮度LED很容易。只要粘在n型和p型半導體上，加上一個小的偏置電壓，當光子流出時就往后退。然而，實際上，這些固態光源絕不簡單。先進的材料和制造工藝結合在一起，生產出了十年前被認為是異想天開的奇異輸出設備。

　　盡管他們生產出令人印象深刻的高效設備，但LED制造商并沒有固步自封。領先的LED企業如Cree公司，歐司朗，和漢城半導體花費數百萬美元在材料科學和制造技術，進一步提升產品的性能。

　　當代高亮度LED已經受益于先進的基板和制造技術，如碳化硅（SiC）和化學氣相沉積（CVD），和明天的芯片將利用像圖案化藍寶石仍然滲透在實驗室材料。本文將仔細研究這些材料和工藝，并評估它們對商業LED性能的影響。

　　Mind the band gap

　　Because the wavelength of the light emitted is a function of the energy band gap of the n- and p-doped semiconductor used to form the junction， engineers are limited in their choice of materials for fabricating LEDs. There is little point in selecting a semiconductor that emits photons that the eye cannot detect.

　　After many years of experimentation and hundreds of millions of research dollars， it turns out that Indium Gallium Nitride （InGaN） – a combination of Gallium Nitride （GaN） and Indium Nitride （InN） – is the best currently available semiconductor for high-brightness LEDs. The band gap of InGaN can be manipulated by altering the ratio of GaN to InN. The chips used at the heart of “white” LEDs， for example， emit photons in the 390 to 440 nanometer part of the spectrum （ultraviolet， violet-blue， and blue）1. These photons are then converted to white light by interaction with phosphor powder.