Innovative advances in LED technology

Innovative advances in LED technology : Innovative advances in LED technology F.K. Yam and Z. Hassan Yam F.K., Hassan Z. Innovative advances in LED technology. Microelectronics Journal (2005), 36 (2), pp. 129-137 Josue De Lara Bashulto

Outline : Outline Introduction History of LEDs Types and applications What are LEDs? Semiconductors A simple diode Electroluminescence LED structures White LEDs Conclusion

History of LEDs : History of LEDs 1960’s 1970’s 1980’s 1990’s Mid 90’s Today Invention of the first LED by Holonyak and Bevacqua. Emitted red light with an efficiency of 0.1 lm/W Green, yellow, and orange LEDs were created and the applications were growing. Calculators, test equipment, digital watches, and displays. Light output continued to improve, brightness increased 10x over previous decade. Applications now included message and outdoor signs. Increased market penetration and more rugged applications. The widespread use of LED in traffic lights. Dr. Shuji Nakamura invented the high brightness blue LED. The basis for white light LEDs. LED’s have achieved efficiencies of ~100 Lm/W. The past months have been an increase in applications as a result of the energy-savings potential.

Semiconductors for LEDs : Semiconductors for LEDs Human eyes are sensitive to certain wavelengths 390<λ<720nm 1.7

What are LEDs? : Semiconductors, diodes, and LEDs explained… What are LEDs?

Semiconductors : Semiconductors

N-Type Material : N-Type Material

P-Type Material : P-Type Material

The Diode : The Diode

The Diode : The Diode

The Diode – no voltage : The Diode – no voltage - - - - - - - - - - - - - - - - N-Type (-) P-Type (+) Depletion Zone

The Diode – with voltage : The Diode – with voltage - - - - - - - - - - - - - - - - N-Type (-) P-Type (+) Depletion Zone

The Diode – with voltage : The Diode – with voltage - - - - - - - - - - - - - - - - N-Type (-) P-Type (+)

The Diode – reversed polarity : The Diode – reversed polarity - - - - - - - - - - - - N-Type (-) P-Type (+) Depletion Zone

Photons : Photons Energy has many forms. Light is one. It is made of packets of energy with momentum but no mass, the photons. Photons are emitted by a variety of phenomena Incandescence, chemiluminescence, sonoluminescence, Mechanoluminescence, and electroluminescence. In an atom, electrons move around the nucleus To jump from lower orbital to a higher one, energy has to be supplied When moving from a higher orbital to a lower one, there is a release in energy hν

LED structures : Quick overview LED structures

LED-structures : LED-structures p-n homojunction Heterostructures Innovative LED structures LEDs with tensile and compressive strained Tunnel junction LEDs with electron reservoir layer Quantum dots LEDS Non-resonant cavity LEDs

White LEDs : White LEDs

White LEDs : White LEDs Produced using two main approaches RGB systems Phosphor conversion LEDs RGB systems combine LEDs with different colors to obtain white light (red, green, and blue). Most efficient method for generating white light Requires complicated control system

Phosphor conversion LEDs : Phosphor conversion LEDs A white LED usually consists of AlInGaN blue LED Phosphor containing epoxy When LED is turned on, the chip emits blue light A portion of the blue light undergoes Stoke’s shift This portion of the light appears amber The amber color compliments the blue light to produce white light Most common white LED Less efficient due to Stoke’s shift Image source:dansdata.com

Conclusions : Conclusions Rapid advances in semiconductor technology have lead to the development of LEDs Every decade the light output of performance LEDs has increased by an order of magnitude Performance is related to LED structure and device design White LED technology, useful for commercial and residential lighting was discussed Efficiency and cost

References : References Yam F.K., Hassan Z. Innovative advances in LED technology. Microelectronics Journal (2005), 36 (2), pp. 129-137. http://electronics.howstuffworks.com/led.htm/ http://www.lighting.philips.com

Thanks : Questions and comments Thanks