Abstract-We report AlGaN-GaN high electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) on SiC substrates with excellent microwave power and efficiency performance. The GaN buffers in these samples were doped with carbon to make them insulating. To reduce gate leakage, a thin silicon nitride film was deposited on the AlGaN surface by chemical vapor deposition. At 4 GHz, an output power density of 6.6 W/mm was obtained with 57% power-added efficiency (PAE) and a gain of 10 dB at a drain bias of 35 V. This is the highest PAE reported until now at 4 GHz in AlGaN-GaN HEMTs grown by MBE. At 10 GHz, we measured an output power density of 7.3 W/mm with a PAE of 36% and gain of 7.6 dB at 40-V drain bias.Index Terms-Carbon, gallium nitride, high electron mobility transistor (HEMT), microwave power, molecular beam epitaxy (MBE), power-added efficiency (PAE), silicon nitride.

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Approved for public release; distribution unlimited. STINFO COPYThis work was funded in whole or in part by Department of the Air Force contract FA8650-05-C-5411. The U.S. Government has for itself and others acting on its behalf an unlimited, paid-up, nonexclusive, irrevocable worldwide license to use, modify, reproduce, release, perform, display, or disclose the work by or on behalf of the U.S. Government. MATERIALS AND MANUFACTURING DIRECTORATE AIR FORCE RESEARCH LABORATORY AIR FORCE MATERIEL COMMAND WRIGHT-PATTERSON AIR FORCE BASE, OH 45433-7750 i REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YY)2. REPORT TYPE 3. DATES COVERED (From -To) SPONSORING/MONITORING AGENCY REPORT NUMBER(S) AFRL-ML-WP-TP-2007-419 DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution unlimited. SUPPLEMENTARY NOTESConference paper submitted to the Proceedings of the 2006 International Microelectronics Symposium. This work was funded in whole or in part by Department of the Air Force contract FA8650-05-C-5411. The U.S. Government has for itself and others acting on its behalf an unlimited, paid-up, nonexclusive, irrevocable worldwide license to use, modify, reproduce, release, perform, display, or disclose the work by or on behalf of the U.S. Government. PAO Case Number: AFRL/WS 06-0307, 06 Feb 2006. ABSTRACTAlGaN/GaN HEMTs on SiC have been fabricated with dual and single gate device geometries. Sub-threshold characteristics and drain bias dependence of large signal parameters were compared to identify differences in electric field. Degradation under RF stress reveals the relative impact of temperature and electric field. The results illustrate the beneficial effects of the dual gate geometry for performance and reliability. SUBJECT TERMS