The Missile Defense Agency (MDA) has awarded Kyma Technologies (Raliegh, NC) numerous Small Business Innovation Research (SBIR) contracts in the area of bulk growth of gallium nitride (GaN) crystals for high-power radio-frequency applications. The latest SBIR was a 2006 Phase I, (awarded in 2007) to develop a means of achieving seeded bulk GaN crystal growth for the production of large-area, high-quality, semi-insulating GaN

substrates for radio frequency (RF) applications. These substrates are expected to improve the performance and reliability of GaN-based power amplifiers for X-band radar applications in missile defense.

The company has demonstrated the ability to increase the size and manufacturability of bulk GaN, and has worked with Department of Defense (DoD) laboratories and academic partners to demonstrate their product in several advanced semiconductor device types of both military and commercial interest.

Bulk GaN is emerging as a viable replacement for silicon carbide and sapphire, which are used to make blue and white LEDs, with many other applications possible in hybrid electric vehicles, sensors, laser diodes, terahertz imaging, and optoelectronic displays.

How it Works

Kyma Technologies’ GaN wafers for optoelectronic applications.
Like all semiconductor devices, GaN semiconductor devices are best produced using a high-quality native substrate. Native substrates are sliced from single-crystal boules and have the same composition as the device layers. Devices fabricated on native substrates have the best thermal, electrical, structural, and opticial properties, which translate at the device level to better performance and reliability. Until now, most GaN devices have been made on foreign substrates such as silicon, silicon carbide, and sapphire, which results in huge defect densities in the GaN device layers that are epitaxially grown on top of the substrate. Native GaN would have been used from the beginning, but it is difficult to produce largely because of the incredible stability of the nitrogen molecule.

Kyma’s mission is to create a high-volume supply of high-quality native GaN substrates. Kyma has made great strides in advancing the capabilities of its proprietary hydride vapor phase epitaxy (HVPE)-based methods of growing “native” GaN, enabling the production of very-low-defect substrates that are getting bigger and better over time.

Kyma’s HVPE process enhancements address the problems of lattice-matching and thermal expansion matching that complicate the crystal growth process and present challenges to increasing the size of “native” GaN. Starting with a GaN seed, the company currently grows crystals that are up to 1 cm thick and up to 3" in diameter. Continuous reduction in post-growth cracking has enabled Kyma to deliver very-high-quality 30-mm-round substrates to the DoD, and full 2" and 3" substrates are in sight. The 1-cm-thick wafer can then be sliced into a dozen or so 500-μm-thick substrates. Kyma expects to grow a 4"-diameter wafer.

Applications for GaN substrates include solid-state lighting (white LEDs), which also opens the possibility of exploiting these LEDs simultaneously for their broadband characteristics, such as transmitting Internet signals. In addition, blue laser diodes are a major target for replacement with GaN. The materials have been demonstrated in high-performance LEDs, laser diodes, UV detectors, RF FETs, and Schottky diode electronic switches.

Other applications are in chemical and biological sensing, solar blind UV light detection, electric drives for transportation, distribution transformers for the power grid, fault-current limiting devices, variable-speed controls for motors, high-voltage DC converter stations, interfaces with storage devices, high-power RF devices (signal jamming), UV LEDs for water purification, terahertz devices for imaging without ionizing radiation (luggage/cargo screening), high-definition TV and video projectors, and avionics/automotive displays.

Where it Stands

Kyma is busily supplying research and development laboratories with wafers. In a five- to ten-year timeframe, the industry expects that silicon carbide will give way to GaN. The combined nitride semiconductor market is expected to exceed $9B this year, with GaN and AlN making up about $500M of that market. Kyma is well positioned to respond to the market as it grows. The company projects that the first shipments of 4"-circular native GaN will be this year.

More Information

For more information on Kyma’s GaN wafers, visit . (Source: Joan Zimmermann/NTTC; MDA TechUpdate, Missile Defense Agency, National Technology Transfer Center Washington Operations)

Defense Tech Briefs Magazine

This article first appeared in the June, 2010 issue of Defense Tech Briefs Magazine.

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