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... orate 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. effect transistors (HFETs) . Fluctuations originate at a microscopic level and provide information on the processes responsible for device operation and degradation. The novel fluctuation-based approach is impelled by recent demonstration of strong correlation of microwave hot-electron fluctuations with frequency performance and degradation of nitride HFETs. The correlation has its genesis in the dissipation of the LO-mode heat accumulated by the non-equilibrium longitudinal optical phonons (hot phonons) confined in the channel that hosts the high-density hot-electron gas subjected to a high electric field. The LO-mode heat causes additional scattering of hot electrons and facilitates defect formation in a different manner than conventional heat accumulated by acoustic phonons. The heat accumulation depends on the supplied electric power and the rate of heat dissipation. We treat the problem in terms of the hot-phonon lifetime responsible for conversion of non-migrant optical phonons into migrant modes. The lifetime is measured over wide ranges of electron densities and supplied electric power. The optimal conditions for heat dissipation are determined and associated with plasmon-assisted disintegration of LO phonons. Signatures of plasmons are experimentally resolved in fluctuations, dissipation, hot-electron transport, transistor frequency performance, and device reliability. In particular, a slower degradation and a faster operation of GaN-based HFETs is demonstrated when the plasmon-assisted ultrafast dissipation of the LO-mode heat comes into play. SUBJECT TERMS EOARD , solid state electronics, Electronic Materials 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18, NUMBER OF PAGES 30 19a. NAME OF RESPONSIBLE PERSON SCOTT DUDLEY, Lt Col, USAF a. REPORT UNCLAS b. ABSTRACT UNCLAS c. THIS PAGE UNCLAS 19b. TELEPHONE NUMBER (Include area code) +44 (0)1895 616162 Standard Form 298 (Rev. 8/98)