Gallium nitride (GaN) semiconducting materials have been widely touted for optoelectronic applications such as high-intensity blue LEDs (light-emitting diodes) for color displays, and the blue laser diode, which is likely to increase by fourfold the storage capacity of optical media such as CDs. But GaN also promises to have a large impact on electronics, making possible the creation of transistors with ten times better power handling than current semiconductor devices provide. New transistors that could amplify very large electrical signals-under operating conditions that would literally vaporize ordinary devices-will have many applications in wireless communication and radar systems.

Internationally known for its outstanding research on gallium nitride materials and devices over the past decade, UCSB has received a new five-year, $6.1 million MURI (Multidisciplinary University Research Initiative) grant from the Office of Naval Research to continue advanced work in the area. The research effort, Center for Advanced Nitride Electronics (CANE), will develop or improve the fundamental scientific understanding of physical mechanisms governing the noise behavior of wide bandgap GaN-Based transistors and circuits, and will apply that knowledge in order to achieve breakthrough performance.

Led by electrical and computer engineers Umesh K. Mishra and Robert A. York, CANE also involves materials scientists James S. Speck, Steven P. DenBaars, and Shuji Nakamura; electrical and computer engineer Evelyn L. Hu and four faculty from other nationally prominent research universities: the California Institute of Technology (A. Hajimiri), the University of Michigan (J.Singh), Ohio State University (S. Ringel), Wright State University (D. Look), and VA Tech (R. Trew). The research team will advance UCSB's pioneering work in high-power devices, focusing on the unique opportunity that GaN-based transistors offer to simultaneously achieve both high-power and low noise from amplifiers. Low-noise operation is critical for certain types of commercial and military radar systems; for example, the ability to detect distant objects is ultimately linked to the electronics' noise performance. The CANE research attempts to separate the impact of the underlying materials, device design, and circuit topology on noise-and subsequently to improve each aspect of the problem in order to optimize the electronics' overall noise performance. With the addition of CANE, approximately 35 graduate research assistants are involved in the combined GaN research efforts at UCSB.

A 10-watt power amplifier circuit using flip-chip-mounted gallium nitride transistors, developed at UCSB by recent ECE Ph.D. graduate Jane Xu.

One of the team members, Professor Ali Hajimiri from Caltech has introduced a new theory of phase noise which puts Leeson's model of phase noise on a firm theoretical footing. The theory is based on the Effective Impulse Sensitivity function (the Effective ISF) which quantifies the response of the system to a noise impulse. The results of the theory show that the higher the mobility and transconductance of the device the more peaked the effective ISF is (as shown in the figure) and the lower the pahse noise. Simulations of a Colpitts oscillator with channel mobility as a parameter are presented in the table. The fast switching of the transistorsis essential to achieve currentpulses as sharp as possible, and hence transistorswith lowest parasitic capacitance per maximum deliverable current are highly desirable. This effect is particularly important for GaN transistors as they can offer higher mobility and hence faster switching.