BACKGROUND

The Satellite Venture Business Laboratory (SVBL) at Tokushima University is 1 of 24 national labs created from the Ministry of Education's supplementary budget to stimulate the creation of new ideas and new businesses. The SVBL at Tokushima University is a 4-story world-class facility that opened in June 1997 with research focused on the "Nitride Photonic Semiconductor." Key strengths of SVBL are the excellent materials characterization facilities, bulk GaN crystal growth, and thin film deposition. Currently, there are several Ph.D. candidates, master's, and bachelor's students, and 4 foreign post-doctoral researchers working on wide bandgap semiconductors. The SVBL facility is establishing an international reputation and welcomes visits from outside faculty and researchers.

TECHNOLOGY DISCUSSION

The discussion centered on recent results obtained in Professor Sakai's group and on applications of nitrides in electronics. The group is pioneering in bulk GaN crystal growth by sublimation. It has achieved bulk GaN crystal a few mm in diameter. It has also deposited epitaxial layers on these crystals by MOCVD. These bulk crystals have lower defect densities than GaN grown on sapphire. One particularly interesting discovery from the SVBL group is the role of defects on the cathodoluminscence (CL) properties of GaN. Professor Sakai and his students recently observed that defects do indeed lead to dark spot regions. In a comparison of GaN grown on sapphire and bulk GaN, they observed almost no dark spots on the bulk like film. The number of dark spots on the GaN on sapphire appears to correlate with the defect density measured by TEM. Therefore by growing on bulk GaN crystals, one can expect the optical properties to be improved in the future. This work was reported at the 2nd International Conference on Nitride Semiconductors (ICNS-2) and was well received by the community (Suguhara et al. 1998). In addition to the bulk GaN work, Professor Sakai is developing 2-inch GaN wafers in his MOCVD system, which can then be supplied to outside researchers. In the course of his crystal growth research, he has found that when grown on sapphire, GaN low temperature buffers are better than AlN buffers. When asked about MBE technology for GaN growth, Professor Sakai strongly believes that MOCVD has higher quality and will lend itself to mass-production better.

While the focus of the University of Tokushima is on photonic applications of the nitrides, Professor Sakai is quite knowledgeable and interested in the electronic applications as well. An interesting position that Professor Sakai and other Japanese researchers disclosed to the panel is that the "environmentally friendly" nature of GaN and SiC, as opposed to GaAs, is a big incentive for commercial acceptance in the Japanese market. He cited the example of the many cellular phones being used in Japan that contain toxic GaAs chips, which may one day be replaced with GaN or SiC chips. Another application is in the area of "hard electronics." This term applies to semiconductors that can tolerate harsh environments and be run at high powers and high temperatures. He emphasized if the cost of the new wide bandgap devices can be made competitive, then consumers may favor the safer compounds.

LAB TOUR

The panel was given an extensive lab tour of all the SVBL facilities at Tokushima University. Inside a large clean-room, complete processing facilities for blue lasers and LEDs are housed. Two large crystal growth systems, one a MOCVD system and the other a bulk GaN sublimation system, were in full operation. The panel viewed a 2-inch diameter wafer grown in the MOCVD system. It appeared to have a clear mirror-like surface with no signs of large defects. The characterization facilities were excellent, containing high resolution TEM, cathodoluminescence, SEM, secondary ion mass spectroscopy (SIMS), multicrystal X-ray spectrometry, Auger spectrometry, and a low temperature photoluminescence setup.

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