| Summary: | 碩士 === 崑山科技大學 === 電子工程研究所 === 96 === Luminous efficiency of LED（Light-emitting diode）must be improved for general illumination. Two well-known methods to increase luminous efficiency are chip mission-side roughness and substrate surface etching. The patterned sapphire substrate, which is etched regularly before the epitaxy growing in MOCVD, could control the radiation pattern of LED.
Phosphor is one of the most important factors to fabricate white light LED. For examples, high bright white light LED could be made from green or yellow phosphors pumped by blue LED. High efficiency green LED could be fabricated from green phosphor pumping. Cool-white LED could be made from yellow and red emission phosphor. And for lighting or backlighting high CRI（Color Rendering Index）White LED could be fabricated from red and green phosphors pumped by blue LED. Three key issues for color rendering index of white light LED device are blue light LED, phosphor and correlative color temperature. In order to have high color rendering index, two issues described following：wide FWHM（full width at half maximum）and wide phosphor excited light wavelength. If the more covered area of the visible spectrum wavelength we get, the higher CRI we will have.
There are two parts of my experiment. The first is optical simulation by the well-known software TracePro to simulate patterned sapphire substrate. The purpose is to research the effect of different etching structure of patterned sapphire substrate.
The second experiment is to fabricate white light LED from red and green phosphors pumped by blue light LED. The blue light LED we used in our experiment has the wavelength range between 450 and 452.5 nm, and the chip size is 17 mil *14 mil. There are two kinds white light LED we fabricated in the experiment. There are three blue light LED chips bonded in single package of both kinds package. The different of the both packages is mixed phosphor of encapsulation. One of the experimental devices was encapsulated YAG phosphor mixed silicone to fabricate white light. The other is red and green phosphor mixed encapsulation. The compared and focused parameter was luminous efficiency. YAG phosphor pumped white light has the luminous efficiency 72 lm/W, CRI 70, CIE(0.32, 0.33), CCT 5622°K at the operating current 60mA. On another hand, red and green phosphor pumped white light LED has the luminous efficiency 55 lm/W, CRI 90, CIE(0.31, 0.32), CCT 6479°K at the operating current 60mA. We fabricated the red and green phosphor pumped white light LED, and proved that it could has much higher CRI under similar compared conditions, CIE xy and CCT.
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