Events

 
Seminar
GaN-based Light Emitting Devices and Crystal Growth and Electronic Applications of Gallium Nitride Materials

by Prof. Shuji Nakamura and Steven DenBaars, Materials Department, University of California Santa Barbara, USA

Date
 :  21 Mar 2005 (Mon)
Time
 :  11:00am - 12:00noon
Venue  :  Lee Wing Tat Lecture Theatre (LTD)

Abstract
GaN-based light emitting devices and crystal growth - Charge separation due to spontaneous and piezoelectric polarization inherent to the wurtzite structure has deleterious effects on the performance of most C-axis oriented devices. To overcome this problem, nonpolar GaN, such as A-plain and M-plain GaN substrates have been grown by using hydride vapor phase epitaxy (HVPE) at UCSB. Lateral epitaxial overgrowth (LEO) has been demonstrated to be an effective means of eliminating threading dislocations, basal plain stacking faults, and surface pits in A-plain GaN films. The characteristics of LEO A-plain GaN will be discussed. Roughened surface (RS) LEDs have been developed using photo enhanced chemical (PEC) etching. The sapphire substrate was removed by laser lift off. Then, N-face GaN was etched by PEC etching. The output power of the hexagonal cone shaped RS LED was about two to three times higher that that of the conventional flat surface LEDs. Other new devices, such as Micro Cavity (MC) LEDs and UV LEDs with an emission wavelength of 280 nm will also be discussed.

Electronic Applications of Gallium Nitride Materials - GaN based materials have recently shown great promise for electronic device application. In particular, MOCVD grown films of the AlGaN/GaN heterostructure materials exhibit high sheet charge of 2E+13cm-2, and mobilities of 2100cm2/Vsec at room temperature. These materials have been incorporated in high electron mobility transistors (HEMTs) which have achieved RF power densities as high as 18W/mm at X-band frequencies. MOCVD growth of low defect density materials on semi-insulating SiC substrates has played a key role in enabling new devices.


Biography
Professor 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 1988, he spent a year at the University of Florida as a visiting research associate. 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 has received a number of awards, including: the Nishina Memorial Award (1996), MRS Medal Award (1997), IEEE Jack A. Morton Award, the British Rank Prize (1998) and Benjamin Franklin Medal Award (2002). Since 2000, he is a professor of Materials Department of University of California Santa Barbara. He holds more than 100 patents and has published more than 200 papers in this field. 

Dr. Steven P. DenBaars is an Professor of Materials and Co-Director of the Solid-State Lighting Center at the University of California Santa Barbara. From 1988-1991 Prof. DenBaars was a member of the technical staff at Hewlett-Packard's Opkoelectroncis Division involved in the growth and fabrication of visible LEDs. Specific research interests include growth of wide-bandgap semiconductors (GaN based), and their application to Blue LEDs and lasers and high power electronic devices. This research has lead to the first US university demonstration of a Blue GaN laser diode and over 7 patents pending on GaN growth and processing. In 1994 he received a NSF Young Investigator award. He has authored or Co-Authored over 431 technical publications, 150 conference presentation, and 14 patents.

 

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