材料和制造改進(jìn)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(dǎo)體上，加上一個(gè)小的偏置電壓，當(dāng)光子流出時(shí)就往后退。然而，實(shí)際上，這些固態(tài)光源絕不簡(jiǎn)單。先進(jìn)的材料和制造工藝結(jié)合在一起，生產(chǎn)出了十年前被認(rèn)為是異想天開的奇異輸出設(shè)備。

　　盡管他們生產(chǎn)出令人印象深刻的高效設(shè)備，但LED制造商并沒有固步自封。領(lǐng)先的LED企業(yè)如Cree公司，歐司朗，和漢城半導(dǎo)體花費(fèi)數(shù)百萬美元在材料科學(xué)和制造技術(shù)，進(jìn)一步提升產(chǎn)品的性能。

　　當(dāng)代高亮度LED已經(jīng)受益于先進(jìn)的基板和制造技術(shù)，如碳化硅（SiC）和化學(xué)氣相沉積（CVD），和明天的芯片將利用像圖案化藍(lán)寶石仍然滲透在實(shí)驗(yàn)室材料。本文將仔細(xì)研究這些材料和工藝，并評(píng)估它們對(duì)商業(yè)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.