Development of Blue InGaN LEDs and Future lighting
Dr. Shuji Nakamura
UC Santa Barbara
Nobel Laureate, Physics 2014
The development of high brightness blue LEDs and blue laser diodes required many breakthroughs of GaN growth, p-type conductivity control, InGaN growth and device structures using InGaN/GaN double heterostructures. First, I will discuss the history and background story of the key scientific issues solved in order to realize high efficiency solid state lighting. The fundamental discovery of high quality p-type doping by removing hydrogen passivation, and the role of the InGaN layer in achieving high brightness blue LEDs and Laser Diodes will be described.
Next the speaker will talk about the GaN on GaN LEDs developed by Soraa. The peak wall-plug efficiency of the violet is 84%. There is an intrinsic problem of the LEDs that cannot be easily overcome. When we increase the current densities so high, a reduction in efficiency with increasing the current density is observed. This phenomena, referred to as efficiency droop, forces LED manufactures to operate LEDs at lower current densities (and hence reduced light output) than would be possible to prevent excess heating of the device. An alternative method to produce white light is by using a blue laser, as opposed to an LED, in combination with a phosphor. Above the lasing threshold, the carrier density is clamped at threshold, fixing its density. Increases in carrier density beyond the threshold density immediately contribute to stimulated emission, or lasing. Thus, the carrier density is maintained at the lower, threshold density, prohibiting it from reaching densities where the Auger recombination process becomes the dominant recombination process. Auger recombination, with the resulting efficiency droop, does not appreciably occur in blue laser diodes.
Shuji Nakamura was born on May 22, 1954 in Ehime, Japan. He obtained B.E., M.S., and Ph.D. degrees in Electrical Engineering from the University of Tokushima, Japan in 1977, 1979, and 1994, respectively. He joined Nichia Chemical Industries Ltd in 1979. In 1989, he started the research of blue LEDs using group-III nitride materials. In 1993 and 1995, he developed the first group-III nitride-based blue/green LEDs. He also developed the first group-III nitride-based violet laser diodes (LDs) in 1995. He is the 2014 Nobel Laureate in Physics for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources.
Since 2000, he has been a professor of Materials and Electrical & Computer Engineering at the University of California, Santa Barbara. He holds more than 200 US patents and over 300 Japanese patents. He has published over 550 papers in his field. Prof. Nakamura is the Research Director of the Solid State Lighting & Energy Electronics Center and The Cree Chair in Solid State Lighting & Displays. He co-founded Soraa, Inc. in 2008, which operates vertically integrated fabrication facilities in California’s Silicon Valley and Santa Barbara.