BACKGROUND

NEC's main business activities center on computers and communication products. The development of human communication and culture is the company's vision for the 21st century. In fiscal year 1997, NEC had sales of $39 billion. The main product areas are as follows:

• communications systems and equipment
• computers and industrial electronics
• electronic devices

Of particular interest for this report is the fact that NEC is one of the leading producers in the world of compound semiconductor devices for communications (FETs) and photonics (laser diodes). The research for these devices is done both at the research labs in Tsukuba and at NEC factories such as NEC Kansai Electronics.

TECHNOLOGY DISCUSSION

Wide Bandgap Electronics

NEC is quite interested in both electronic and optoelectronic applications of wide bandgap semiconductors. Currently NEC is focusing on GaN as researchers believe it will be the least expensive wide bandgap material to commercialize. The GaN electronic effort was started in 1997, but Dr. Ohno had a clear picture of the areas where he believed GaN will compete. Dr. Ohno has worked on silicon- and GaAs-based FET devices for the last 15 years. He believes the main advantage of wide bandgap semiconductors are the large breakdown voltage, the small Schottky gate leakage (low off-state leakage), and the small hole generation rate (low on-state voltage). The high breakdown field and high frequency performance of GaN make it attractive as a microwave power communication device. The higher allowable operation temperature of GaN was also mentioned as a benefit since it allows for higher heat removal due to the increase in the temperature gradient. In particular NEC company targets for the microwave power GaN high electron mobility transistor (HEMT) are as follows:

• 100 W CW RF power GaN is targeted for 50-100 GHz region
• 100 W part and 500 W module
• drain current density of 0.5 A/mm
• low gate leakage
• p-type GaN (important for on-state resistance)

Dr. Ohno believes that the GaN electronics market is primarily for high frequency satellite and communication base station applications. For cellular phone applications, the competition will be fierce with Si LDMOS coming to a 5 GHz power region soon. Other potential applications of wide bandgap electronics are microwave ovens and anti-collision radar for automobiles and boats. The non-toxic nature of GaN makes it an attractive alternative to GaAs devices, and it would meet ISO 14000 specifications.

Wide Bandgap Optoelectronics

The optoelectronics effort, in particular the blue GaN laser effort, has been ongoing for several years at NEC. Dr. Usui has achieved remarkable success in pioneering the defect reduction in GaN using a lateral epitaxial overgrowth (LEO) method. Dr. Usui uses the acronym FIELO for facet initiated epitaxial lateral overgrowth to describe the NEC technique for defect reduction in GaN. In this technique, having the growing facet steer the edge defect parallel to the surface reduces defects so that they cannot propagate on the surface. The defect density is reduced from 1E+9/cm² to less than 1E+7/cm². He has even made "bulk like" GaN substrates by lifting off thick GaN epitaxial films from the sapphire substrate using a proprietary technique. These bulk like GaN films are 100 to 200 microns thick and 1cm by 1cm wide. Such low defect films can be used to make conventional type edge emitting lasers. Dr. Usui has developed a hydride vapor phase epitaxy (HVPE) method for depositing the thick LEO films on sapphire substrates. The films are grown at 1000°C and are 100 to 200 microns thick after a few hours. The best X-ray line width is 150 arcseconds, and mobilities of 863 cm²/V sec and 2780 cm²/V sec have been obtained at 300° K and 77° K, respectively. The two areas Dr. Usui mentioned that NEC is interested in are the blue laser for DVD applications and the white LED for lighting and LCD backlighting. For the white lighting applications of GaN, Dr. Usui mentioned the large Japanese government supported program to develop more energy efficient light sources. The blue DVD laser will have wide ranging applications in the future high information society in which DVD drives will be found in DVD-ROM for road maps, DVD drive for home computers, and DVD for home entertainment. Other potential consumer applications that require higher output powers at lower costs are blue and green laser diodes for projection displays and laser printing. NEC's research in these areas is first rate, and these products will no doubt be achieved.