New Class of GaN-Based Laser Diode Created

A research team that included the inventor of the blue laser diode has created the first nonpolar blue-violet laser diodes, which have applications in optical data storage, optical sensing, communications and medicine.

The researchers, from the Solid State Lighting and Display Center (SSLDC) in the University of California, Santa Barbara's College of Engineering, were led by blue laser diode creator Shuji Nakamura, winner of the 2006 Millennium Technology Prize. The team achieved lasing operation in nonpolar gallium nitride (GaN) semiconductors and demonstrated what they said is the world's first nonpolar blue-violet laser diodes. They could be used commercially in high-density optical data storage for high-definition displays and video, in optical sensing, and in medical applications. Because of the shorter wavelength of emission in these devices, they can accommodate higher densities of optical storage than conventional red-laser based systems, the researchers said.

The far-field pattern of the world's first gallium nitride (GaN) nonpolar blue-violet laser diodes is shown. The bright spots illustrate clear lasing modes. (Photo: University of California, Santa Barbara Solid State Lighting and Display Center)

Nakamura, a professor in UCSB's Department of Materials in the College of Engineering, is internationally known for his invention of new light sources: blue, green, and white LEDs and the blue laser diode. He and two of his faculty colleagues, professors Steven DenBaars and James Speck, directed the work of two graduate students, Mathew Schmidt and Kwang Choong Kim, who fabricated the new diodes.

"Our initial results of the first violet nonpolar laser diodes with a low threshold current density demonstrate a high possibility that current c-plane violet laser diodes used for HD-DVD and Blue Ray DVD could soon be replaced with nonpolar violet laser diodes, which require lower operating power and have longer lifetimes," Nakamura said.

The new blue-violet laser diodes displayed threshold current densities as low as 7.5 kA/cm2, clear far-field pattern and a lasing wavelength of 405 nm under pulsed operation. This new class of gallium nitride-based laser diode is based on novel nonpolar orientations of GaN that were pioneered at UCSB, the researchers said. Devices based on nonpolar GaN semiconductors are expected to yield lower threshold current than the commercially available c-plane devices. These new orientations of GaN will result in laser diodes with lower operating power and longer lifetimes, which are necessary for high-performance operation.

"This is a groundbreaking advancement in laser diodes and a major step in solid-state lighting technology," said UCSB Chancellor Henry T. Yang. "The blue-violet laser will improve high density optical data storage for high-definition TV, video discs and optical sensors, and will also have applications in and long-term benefits for the communication, entertainment, medical and environmental areas."

Matthew Tirrell, dean of the College of Engineering, said he was proud that his colleagues are achieving breakthroughs "not only in solid-state light sources for data storage and display systems, but also in energy efficient technologies that will have impact on people's lives for decades to come."

Funding for the latest research was provided jointly by the SSLDC and the Japan Science & Technology Agency's Exploratory Research for Advanced Technology program.

The findings have now been submitted for publication. A public demonstration of the nonpolar blue-violet laser is being planned for early February at the university.

For more information, visit: www.ucsb.edu