AlGaN/GaN HEMTs—An Overview of Device Operation and Applications UMESH K. MISHRA, FELLOW, IEEE, PRIMIT PARIKH, AND YI-FENG WU Invited Paper Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications from power conditioning to microwave transmitters for communications and radar. Of the var- ious materials and device technologies, the AlGaN/GaN high-elec- tron mobility transistor seems the most promising. This paper at- tempts to present the status of the technology and the market with a view of highlighting both the progress and the remaining problems. Keywords—Gallium nitride, high-electron mobility transistor (HEMTs), MMICs, polarization. I. INTRODUCTION AND MARKET ANALYSIS As the market for cellular, personal communications services, and broad-band access are expanding and third- generation (3G) mobile systems coming closer to reality, radio frequency (RF) and microwave power amplifiers are beginning to be the focus of attention. A variety of power- amplifier technologies are vying for market share, such as Si lateral-diffused metal–oxide–semiconductors and bipolar transistors, GaAs metal–semiconductor field-effect transis- tors (MESFETs), GaAs (or GaAs/InGaP) heterojunction bipolar transistors, SiC MESFETs, and GaN high-electron mobility transistors (HEMTs). The materials properties of GaN compared to the com- peting materials is presented in Table 1. The resulting competitive advantages of GaN devices and amplifiers for a commercial product are described in Table 2. The first column states the required performance benchmarks for any technology for power devices and the second column Manuscript received October 4, 2001; revised January 26, 2002. This work was supported by the Office of Naval Research, Air Force Office of Scientific Research, Defense Advanced Research Projects Agency, Ballistic Missile Defense Organization, and Small Business Innovative Research pro- grams. U. K. Mishra is with the Electrical and Computer Engineering Depart- ment, Engineering I, University of California, Santa Barbara, Santa Barbara, CA 93106 USA. P. Parikh and Y.-F. Wu are with Cree Lighting Company, Goleta, CA 93117 USA. Publisher Item Identifier S 0018-9219(02)05582-2. Table 1 Table of Properties of Competing Materials in Power Electronics lists the enabling feature of GaN-based devices that fulfill this need. In every single category, GaN devices excel over conventional technology. The last column summarizes the re- sulting performance advantages at the system level and to the customer. The highlighted features offer the most signif- icant product benefits. The high power per unit width trans- lates into smaller devices that are not only easier to fabricate, but also offer much higher impedance. This makes it much easier to match them to the system, which is often a complex task with conventional devices in GaAs (for e.g., a matching ratio ten times larger might be needed for a GaAs transistor, increasing overall complexity and cost). The high-voltage feature eliminates or at least reduces the need for voltage conversion. Commercial systems (e.g., wireless base station) operate at 28 V and a low-voltage technology would need voltage step down from 28 V to the required voltage. How- ever, GaN devices can easily operate at 28 V and poten- tially up to 42 V. The higher efficiency that results from this high operating voltage reduces power requirements and simplifies cooling, an important advantage, since cost and weight of cooling systems is a significant fraction of the cost of a high-power microwave transmitter. The nitride tech- nology is also the critical enabler for blue, green, and white lighting. The commercial lighting market is a multibillion dollar market. While some of the requirements for RF and microwave applications are different (such as the need for a semiinsulating substrate), there is no doubt that exercising 0018-9219/02$17.00 © 2002 IEEE 1022 PROCEEDINGS OF THE IEEE, VOL. 90, NO. 6, JUNE 2002