L. Pavesi Fisica UNITN

Transcription

1 L. Pavesi Fisica UNITN

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3 Programma 1) Cosa sono i LED 2) Cosa hanno fatto per meritarsi un Nobel 3) Perché la loro scoperta è importante 4) Futuro

4 COSA SONO I LED

5 Cosa sono i LED Diodi elettroluminescenti Light Emitting Diode Dispositivi a semiconduttore (piccoli robusti) Sono basati su di una giunzione pn Dispositivi a iniezione elettrica Opposto di una cella solare

6 Dispositivi a semiconduttore

7 Drogaggio di tipo p e di tipo n

8 Dispositivi ad iniezione elettrica: LED

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12 Per cambiare colore cambio semiconduttore

13 Per cambiare colore cambio semiconduttore Semiconduttori III V

14 COSA HANNO FATTO PER MERITARSI IL NOBEL

15 Semiconduttori Scoperti e sintetizzati alla fine dell ottocento Usati durante la seconda guerra mondiale per radar 1947 scoperta del transistor 1960 scoperta del laser 1962 primo laser a semiconduttore 1970 primo microprocessore

16 Nick Holonyak 1962 LED a luce rossa

17 1968 LED a luce rossa: prima produzione di massa Hewlett Packard calculators

18 1980 LED a luce rossa, verde, gialla

19 Mancano LED a luce blue

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21 Quali erano i problemi Difetti di crescita dovuti a differenti passi reticolari Incapacità di crescere materiali drogati p

22 The Laureates challenged established truths; they worked hard and took considerable risks. They built their equipment themselves, learnt the technology, and carried out thousands of experiments. Most of the time they failed, but they did not despair; this was laboratory artistry at the highest level. 22

23 .But my bosses said it would be impossible to create a blue LED at Nichia, because many big companies and many research teams in big universities were trying to do it and were failing. So I went to went to my company s chairman, Nobuo Ogawa, who was my professor s friend, and the president Eji Ogawa, who was his son-in-law. I asked them if they would let me do research on blue LEDs and they said "Sure. No problem. Go ahead." I was very surprised. I asked them to give me a large budget so I could do it. "Please give me three million U.S. dollars," and they said "Sure. No problem." They had faith in me, despite the dismal sales (interview 2004 to Nakamura) 23

24 Soluzioni Strato intermedio Riscaldamento per rompere legame H Mg e quindi drogare p (Mg group II Ga group III)

25 Blue LED: struttura

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27 Timeline 1973 Akasaki started GaN based blue LED research 1985 High quality GaN crystals (A&A) 1988 GaN project (N) 1989 p type doping by electron bombardement (A&A) 1989 first blue LED (A&A) 1991 industrial growth of GaN (N) 1992 p type doping heating (N) 1991 blue LED (N) 1994 first bright DH blue LED > 250x competitors (N) 1996 CW blue violet laser diode (N) 1999 Blue laser diode commercially available Akasaki Amano University Nakamura company

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30 White LEDs 1st technique: Found in 1993, when the first blue LED was produced. By juxtaposing at a certain distance blue, red, and green LEDs, white light was obtained. Most simple method but not often used nowadays. 2nd technique: found in 1996 by Nichia Corp. and Fraunhofer Institut Start with LED with an active layer made of InGaN Cover this structure is covered with a yellow phosphor crystal coating (Ce 3+ :YAG). The LED chip emits blue light, which is converted to yellow light by the phosphor. Phosphorescence Luminescence

31 Luce bianca - 3 led: rosso, verde, blu 31

32 Luce bianca LED blu + fosfori 32

33 Japanese Company to Pay Ex Employee $8.1 Million for Invention (NYT Jan 12, 2005) Nakamura joined Nichia after graduating with a master's degree in electrical engineering from Tokushima University in In 1990, he filed the "404 patent, "which covered a technique to grow gallium nitride crystals, an essential component of blue LEDs. Using Nakamura's method, Nichia produced and sold the first high brightness blue LEDs in 1993 and quickly reaped huge profits. Nakamura left Nichia in December 1999 to join the University of California, Santa Barbara the following February. In December 2000, Nichia filed a lawsuit against Nakamura in the U.S. for infringing trade secrets. Nakamura then counter sued Nichia in a Tokyo court, seeking ownership of the 404 patent and compensation for his contributions to developing blue LEDs. Nakamura sued his former employer, seeking a share of the royalties from his invention after the company gave him an award of 20,000 yen, or less than $200, for his work. The amount of the settlement was significantly smaller than the 20 billion yen, nearly $200 million, that a lower court ordered Nichia to pay Mr. Nakamura last year. The lower court said that would be a fair amount, given that his invention was worth about 60 billion yen, or roughly $580 million, to Nichia.

34 PERCHÉ LA LORO SCOPERTA È IMPORTANTE

35 È un Nobel nello spirito di Alfred Nobel: Premiare le invenzioni e gli studi che hanno una tangibile ricaduta sull'umanità.

36 World Lighting Pollution Lighting corresponds to 20% of the worldwide energy consumption. Reducing energy consumption by using LEDs will significantly reduce the level of CO 2 emissions, therefore positively impacting climate change Reduced heat generation Use of less power Longer life span

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38 Se tutte le luci del mondo fossero a LED: 38

39 History of Lighting 3 traditional Technologies: Fire Incandescence Fluorescence & High Intensity discharge Oil lamp Incandescent bulbs Fluorescent bulbs

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44 The Promise Energy Usage Comparison Best White LED and Compact Fluorescent vs. 60Watt Light Bulb Comparison 60 53watts saved Power Used (Watts) W Bulb Compact Fluor. LED 0 Light Source

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48 White LED GaN or InGaN LED Ce:YAG 3 kinds of white light, depending on the temperature: K, Incandescant or warm white K, Pure white K, Cool white

49 Color temperature and color mixing An LED gives a pure monochromatic colour (on the edges of the CIE diagramm) By mixing these colours a new one can be obtained. CIE diagram of human vision

50 The Advantage of LED Lighting Long life lifetimes can exceed 100,000 hours as compared to 1,000 hrs for tungsten bulbs. Robustness no moving parts, no glass, no filaments. Size typical package is only 5 mm in diameter. Energy efficiency 50 90% less energy used translates into smaller power supply. Non toxicity no mercury. Versatility available in a variety of colors; can be pulsed. Cool less heat radiation than HID or incandescent

51 LED Market Penetration Time LED Market Penetration

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55 Good efficiency & durability Associated with perfect material and devices, LEDs would require only 3 Watts to generate the light obtained with a 60 Watt incandescent bulb LEDscanprovide hrs (5,7 years) of life compared to 1000 hrs with incandescent light bulbs Figure 1. LED vs. conventional light sources degradation in light output over time

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59 8 Applications Common application: Digital clock, battery level indicator, torch Traffic signals, street light Buildings Outdoor: runway in airports Residential Information boards

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61 Current LED Market US$25.82 billion in 2014 Cellphone (Nokia) Large Displays (NASDAQ) streetlights TVs (LED DLP tm ) (samsung) Automotive

62 Ultra Mobile LED Enabled products Uses Blue, Green, Red LEDs CellPhone Camera Flash (Osram Opto)

63 FUTURO

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79 Conclusions We are on the dwn of new light Technologies: Light+electronics+sensor+design This has been made possible by the hard work of scientists which were able to look behind the common sense Blue LED is a success story due to the efforts of only few individuals