Nakamura hints at improved GaN structures
Shuji Nakamura has revealed sketchy details about thin GaN films that could result in brighter sources for solid-state lighting, according to a report in Japan's Nihon Keizai Shimbun newspaper.
It suggests that Nakamura's team at the University of California, Santa Barbara (UCSB) has developed a process to make non-polar and semi-polar GaN crystals.
Although Nakamura is reported to have held a press conference in Tokyo to reveal the development, he was unwilling to provide much detail of the process involved because of intellectual property concerns.
But the GaN pioneer may have revealed more in his recent plenary talk at the International Conference on Nitride Semiconductors (ICNS) held in Bremen, Germany.
In the talk, Nakamura said that charge separation effects due to polarization have a negative effect on the performance of most GaN devices oriented in the C-axis.
To overcome the problem, the UCSB team has worked on non-polar A-plane and M-plane GaN substrates grown by hydride vapor phase epitaxy (HVPE).
Blue LEDs grown on non-polar GaN showed a relatively small turn-on voltage and Nakamura added that the blue-shift of the peak emission wavelength with increasing forward current was decreased dramatically.
Other new devices have also been fabricated, such as micro-cavity LEDs.
